Control Tools

• Diagnostics availability

• Commercial diagnostic kits available worldwide

  This Disease and Product Analysis (DPA) is “policy neutral”; we have adhered to the natural science evidence base. “Disease: Mammalian tuberculosis (TB)” is a chronic bacterial disease of animals, including humans, caused by host-adapted members of the Mycobacterium tuberculosis complex (MTBC). Regarding livestock and wildlife hosts, we refer mostly to infection with M. bovis and other animal-adapted variants, such as M. caprae. World Organisation of Animal Health (WOAH 2022, founded as OIE), EU Bovine TB Task Force subgroup and recently the EU Animal Health law (Regulation 2016/429) support this “mammalian TB” nomenclature.

  Yes, antemortem test reagents, or complete tests, are commercially available. Diagnosis tends to be based on cell-mediated immunity (CMI). Production tends to be centred in a few territories; tests are for the most part expensive.

  Specialist culture is the reference standard (no gold standard) for postmortem diagnosis and confirmation in reference laboratories but is increasingly being replaced by validated PCR-based tests.

  List of commercially available diagnostics (Diagnostics for Animals).

  GAPS :

  Availability of less expensive tests, with improved performance characteristics, especially sensitivity (Se).

  Improved understanding of cellular and humoral immune responses post-infection, including dose response and impact of concurrent infections. Improved understanding of pathogenesis and spectrum of exposure outcomes related to immune-based tests and direct pathogen detection.

  Require improved and validated diagnostic tests and reagents; for example, skin tests based on more defined antigens, improved serological and molecular detection products, alongside detection of immune surrogates.

• Diagnostic kits validated by International, European or National Standards

  Various types of delayed type hypersensitivity (DTH) tuberculin skin test and Interferon Gamma Release Assays (IGRAs) are approved for use by WOAH directly, or as supplementary, in several national programme, including in the European Union, USA, Chile, and New Zealand. Rational deployment of IGRAs, to augment tuberculin testing, has contributed to reduced prevalence in several territories.A small number of commercial molecular/serological tests are listed on the WOAH register of diagnostic kits (commercial identity withheld); some territories allow their use, supplementary to official tests, often at herd keeper risk and expense. Competent Authorities may require additional validation assurance before such tests could be considered for official use. In some species these can be the frontline tests (deer, SACs).It seems reasonable to assume that optimal diagnosis requires efficient host immune function.Comparative tuberculin skin testing can be used in SACs, pigs, sheep, goats, and deer. As with cattle, the skin test is the internationally accepted test for M. bovis in live animals, although its performance is less well understood.IGRAs have been tested on alpacas under UK conditions.Antibody tests, validated under UK conditions, are available for statutory testing of SACs; no antibody tests are validated in the UK for sheep, pigs, goats, or deer.

  GAPS :

  Availability of independent, sufficiently powered, replicated, and controlled test evaluation and validation for various sample types if performance merits.

• Diagnostic method(s) described by International, European or National standards

  Please refer to the WOAH and WHO sites regarding official cattle tests:

  https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/?id=169&L=1&htmfile=chapitre_bovine_tuberculosis.htm

  https://www.woah.org/fileadmin/Home/eng/Health_standards/tahm/3.01.13_Mammalian_tuberculosis.pdf

  https://www.who.int/teams/global-tuberculosis-programmeme/zoonotic-tbhttps://www.who.int/teams/global-tuberculosis-programmeme/zoonotic-tb

  https://www.who.int/publications/i/item/9789241513043

  https://www.visavet.es/bovinetuberculosis/

  Variations in tuberculin skin testing protocols remain the cornerstone of official livestock TB control programmes. These can be direct (Single intradermal cervical test, SICT) or comparative (Single intradermal comparative tuberculin test, SICCT) where confounding influences of cross-reactive environmental mycobacteria can be problematic. Cut-off interpretation points can be altered via a test result matrix to improve diagnostic sensitivity (standard, severe, super severe etc.), often at the expense of specificity.When interpreted for high specificity, animal-level diagnostic sensitivity tends to be moderate and context dependent (i.e., refers only to the conditions that apply to the study reported), especially for SICCT (55-94%); the sensitivity of SICCT, cervical, or caudal fold tests can be impacted by tuberculin dose. Caudal fold tests tend to be less sensitive than cervical tests.Blood interferon gamma release assays (IGRAs) are listed as additional supplementary tests for cattle diagnosis. While more sensitive (median ~88%) than tuberculin tests, specificity (median ~96%) tends to be lower. At EU level, IGRAs can be used at the same level as the tuberculin skin test with the purpose of granting and maintaining disease-free status for infection with M. tuberculosis complex in bovines and for movement of bovine and caprine animals within the EU; cut-off differs from the one used for eradication purposes.Bovine tuberculin is manufactured internationally from M. bovis variant AN5. There is evidence of between manufacturer and within manufacturer batch variation in tuberculins, which are challenging to quality control.Research to develop and evaluate molecularly defined tuberculin (MDT) has progressed; if shown to offer improved performance, MDT would offer advantages in production, QC, consistency, 3Rs etc.This diagnostic gap is also well-recognised in human TB where only 63% of new cases were confirmed by culture. WHO issued a call and target product profiles to develop new triage tests, with predefined sensitivity and specificity thresholds.

  GAPS :

  Advanced statistical modeling required - latent class analyses etc. assuming no gold standard, meta-analysis of test performance.Need to understand better current mammalian TB test performance characteristics - separately and in combination(s), in different settings, samples, and animal types, whether/when confounded by concurrent infection(s), such as BVD, helminths, Johne’s disease etc., economic cost versus epidemiological benefit provided by various test cut-offs.Improve tuberculin QC and potency testing. Research synthetic (modified peptides, recombinant antigens etc.) alternatives.Further evaluation of MDT (not to be confused with DIVA testing) is warranted.

• Commercial potential for diagnostic kits in Europe

  Moderate; in most territories the main customer remains the Competent Authority tasked with managing the official control programme, using official tests. The route for a new test to achieve official approval is probably not clear, unlike for some other diseases.

  GAPS :

  Sufficiently powered independent evaluations required, leading to objective validation data.Advanced statistical modeling required - latent class analyses etc., assuming no gold standard, meta-analysis of test performance.Need to understand better current mammalian TB test performance characteristics - separately and in combination(s), in different settings, samples, and animal types, whether/when confounded by concurrent infection(s), yield by test/combination, economic cost versus epidemiological benefit. A practical constraint in mammalian TB control is the balance between disease eradication and economic reality/maintaining a viable industry.Investigate novel tests for bulk milk testing etc.Define the performance characteristics (%Se, %Sp) required of a potential first line and second line test to be considered equivalent to official test(s) using standard test panels.

• DIVA tests required and/or available

  A DIVA test (tuberculin skin test or IGRA) with validated performance characteristics would be required in situations where animals (predominantly cattle) were vaccinated with M. bovis BCG; the tuberculin skin test does not currently differentiate between infected and BCG-vaccinated animals. IGRAs and tuberculin skin tests, based on specific antigens, such as ESAT-6 and CFP-10, are used for human TB diagnosis. BCG vaccination has recently been shown to reduce M. bovis susceptibility and transmission in cattle field trials in Ethiopia. Efficacy and safety trials of DIVA tests are underway.

  GAPS :

  Sufficiently powered vaccine efficacy and DIVA performance characteristics tests are underway in some territories; outcomes likely to be context dependent.

• Vaccines availability

• Commercial vaccines availability (globally)

  Yes, in principle, the lead candidate remains M. bovis BCG, a live attenuated strain (and various locally diverged sub-variants) of M. bovis used extensively in human vaccination, where it provides solid protection against generalised TB, especially in neonates; its effectiveness against pulmonary TB in adolescents and adults, which is the global human TB burden, is questionable/variable.BCG vaccination in cattle is not permitted in the EU or UK. Earlier studies with BCG showed variable efficacy in cattle at population and individual animal levels. As with BCG in humans, such variation may be context dependent and attributable to various factors including vaccine formulation, dose, route of vaccination, and the degree of exposure to environmental mycobacteria.BCG field trials have been performed, although the variability of experimental and trial designs makes meaningful comparisons difficult. More recent field experiments in Ethiopia and Mexico show that BCG vaccination can reduce susceptibility in cattle. However, BCG vaccination cross reacts with official immunodiagnostic tests, requiring the development of a DIVA test.Safety and duration of immunity studies are to be assessed by regulators; a dossier for licensing BCG deployment in cattle in the UK is in preparation and field trials of DIVA tests are underway.BCG can reduce susceptibility and pathology in other domestic and wildlife species such as goats, deer, badgers, and possums and is licensed for vaccination of badgers in the UK and Ireland.The mammalian TB vaccine research community communicates and collaborates closely with the human TB vaccine community. New candidate vaccines are currently being screened with heterologous prime-boost vaccine protocols based on BCG vaccination in combination with viral, protein, or DNA subunits.Substantial work has been done to formulate oral baits for vaccine delivery to wildlife; concerns remain over variability of uptake and role of non-target species; this approach has been discontinued in some territories.

  GAPS :

  Efficacy trials of BCG vaccination and matched DIVA tests in cattle.Field studies (under natural conditions) to determine dose, route, timing of vaccination and duration of immunity in livestock and wildlife.Field trials of subunit vaccine candidates, in prime-boost protocols with BCG. Investigate possibility of a vaccine/subunit to boost the efficacy of BCG. Additional research to evaluate potential of alternative vaccine delivery strategies, virally vectored etc.Research to investigate potential of passive transfer between vaccinees.Research to investigate the host genetics of BCG, or other vaccine candidate, responses in cattle.

• Marker vaccines available worldwide

  Not available. BCG could be considered a marker vaccine in the sense that genes deleted from wild type M. bovis during attenuation can be exploited as DIVA antigens (e.g., ESAT-6), while other BCG antigens further increase the repertoire of potential DIVA reagents (e.g., Rv3615c). BCG is readily identifiable by molecular tests. Research is underway to develop additional marker vaccines.

  An alternative approach to generate vaccine-compatible reagents used transposon mutagenesis of M. bovis BCG and gene editing to knock out BCG genes that were then included as DIVA reagents; such approaches require sufficiently powered and replicated field trials.

• Effectiveness of vaccines / Main shortcomings of current vaccines

  Injectable BCG remains the lead and best characterised vaccine candidate for livestock and wildlife applications, although oral baited vaccines are being trialled in some settings, such as Spain, and Michigan.While not providing complete or sterile immunity, consensus from several studies is that BCG vaccination can reduce susceptibility and substantially reduce M. bovis-induced pathology, with an assumed reduction in transmissibility.A recent, relatively small, and context-dependent field trial in Ethiopia estimated “transmission rates” alongside “vaccine efficacy” in cattle (i.e., 39% end-point “vaccine efficacy”, as well as estimates for “transmission rate efficacy” of 58% direct, 74% indirect, and 89% total). “Efficacy” was measured for 1 year; “incubation period” is known to be highly variable.Recent “non-inferiority” field trial data from Ireland showed BCG reduced susceptibility in badgers, but without impacting onward transmission in infected badgers.

  BCG will compromise official tuberculin-based skin or blood tests; cattle vaccination with BCG should not be used in territories where control or trade measures are based on such testing; BCG vaccination therefore will require the application of validated DIVA tests, with acceptable performance characteristics.Duration of immunity from BCG vaccination in cattle is 1-2 years; therefore, regular revaccinations may be required; recent studies support extending BCG-induced immunity through revaccination. Recent GLP safety studies support BCG safety, although they require regulatory authority assessment.Injectable BCG vaccination may be considered for deployment to reduce spread of M. bovis in wildlife reservoirs. Such studies, which are likely to be context dependent, require extensive planning, preferably supported by epidemiological (and economic) modelling.

  Although BCG is readily isolated from the injection site, there is limited evidence that BCG is excreted extensively from vaccinates to other livestock, wildlife, or the environment, or vice versa, where it could confound diagnostics in the absence of a DIVA test. However, in contact unvaccinated white-tailed deer were infected with BCG by other vaccinated white-tailed deer. While BCG sub-strains have been evaluated in animals, future vaccine candidate research needs to be alert to the extent to which they provide cover against extant or emerging variants of M. bovis.

  GAPS :

  Further research, including field studies under natural conditions, on duration of BCG-induced vaccine efficacy and potential benefits from revaccination of livestock and/or wildlife.As with human TB, correlates of immune protection are not understood.Parameterise mathematical models, with context-dependent estimates where available, to investigate vaccine efficacy and simulate deployment options in a multi-host (cross species) epi-system including cattle-based controls and which may include a component of M. bovis transmission via a contaminated environment.

  Research to develop and evaluate alternative BCG delivery options for wildlife.Research to understand the role of candidate vaccine dose and route (aerosol, intramuscular, intradermal, subcutaneous, intranasal, intratracheal, oral etc.,) and potential for mucosal immunity.Field efficacy of BCG and effectiveness of proposed DIVA in different geographies has yet to be determined.Immunological biomarkers required to define individual animals as protected post-BCG vaccination.

• Commercial potential for vaccines in Europe

  At present vaccination of cattle against mammalian TB is not permitted in Europe. There is some commercial potential beyond the EU, including where wildlife acts as a reservoir of infection, depending on existing national and international trading rules.

  Injectable BCG remains the lead candidate vaccine for consideration in livestock and wildlife, although challenging to deliver. In the human TB field, several modified BCG candidates, virus-vectored, and sub-unit vaccines, with or without adjuvant, are undergoing advanced field trials.

  The international mammalian TB research community collaborates closely with human TB colleagues and new candidates will be identified and evaluated appropriately.

• Regulatory and/or policy challenges to approval

  EU acceptance of cattle TB vaccination would need to be negotiated and evidenced. Provision of data to justify the (market) authorisation of vaccines in term of safety, efficacy and quality may be difficult and expensive to generate. EFSA have published an opinion on what would be required to allow TB vaccination of cattle in the EU. http://www.efsa.europa.eu/en/efsajournal/pub/3475.

  Wildlife vaccination may be relatively easier to implement, as less legal obstacles exist in the EU in relation to wildlife vaccines.Should a DIVA test become available, which permits BCG cattle vaccination, trading blocs or partners will need to consider their legislative requirements.National positions regarding acceptability of genetic modification and gene editing may become limiting should such vaccines become candidates.

• Commercial feasibility (e.g manufacturing)

  BCG is manufactured to quality standards at a limited number of approved sites. There have been global shortages of BCG vaccine for human deployment, necessitating limits on BCG manufacture and deployment for animal use. The BCG variant used differs historically by country but would tend to be BCG Danish (or historically BCG Pasteur). Some BCG variants with different evolutionary history differ in properties, including potency and antigen complement, and may cross-react with some diagnostic tests.Difficulties in vaccine manufacture would depend on the biological nature of the candidate.

• Opportunity for barrier protection

  The opportunity exists for barrier protection using a range of host-directed interventions, but would be a policy decision based on experimental, field trial, and RCT data, modelling, epidemiological evidence and economic option appraisal. Availability of a well characterised and approved DIVA test(s) would be a prerequisite for deployment in livestock. Ring vaccination in wildlife possibly more feasible but requires evaluation.

  GAPS :

  Requires epidemiological modelling support and sufficiently powered and replicated field trials, ideally RCTs.Requires epidemiological modelling support and sufficiently powered and replicated field trials, ideally RCTs.

• Pharmaceutical availability

• Current therapy (curative and preventive)

  Antimicrobial treatment of livestock for mammalian TB infection is not permitted: no drugs are licensed in the EU or UK for the treatment of livestock with diagnosed mammalian TB.In principle, therapeutics might work but disadvantages would likely outweigh advantages. In R&D, infected cattle have been treated with anti-TB drugs, which had a demonstrable effect in reducing IGRA responses, which increased when treatment was halted.

• Future therapy

  Not applicable currently.

• Commercial potential for pharmaceuticals in Europe

  Not applicable currently. Not applicable currently.

• Regulatory and/or policy challenges to approval

  Not applicable currently.

• Commercial feasibility (e.g manufacturing)

  Not applicable currently.

• New developments for diagnostic tests

• Requirements for diagnostics development

  Requirements:

  • CMI, humoral, and pathogen/antigen-based diagnostics with improved performance i.e., sensitivity, specificity, PPV, NPV (both dependent on field/epi/true prevalence setting where applied), throughput, speed, cost.
  • Diagnostic assays with objective and reproducible read out: in vitro
  • Tuberculin should be standardized in terms of activity/potency for in vivo and in vitro detection assays.
  • Alternative and more standardized methods (in vitro) for potency testing should be developed.
  • Improved antigens (addition/replacement to tuberculin, MDT etc.) needed for improved CMI detection assays. Those that have been developed need to be validated.
  • DIVA reagents should be developed further and those available need to be validated.
  • Sensitivity of serodiagnosis tests needs to be increased.
  • Improved animal-side diagnostic tests for wildlife species, which represent a reservoir for mammalian TB, required.

  GAPS :

  Sufficiently powered independent evaluations required, leading to validation data.Testing algorithm is important for assessing test performance, i.e., whether parallel/series interpretation of two or more tests.Advanced statistical modeling required - latent class analyses etc. assuming no gold standard, meta-analysis of test performance.Need to understand better current mammalian TB test performance characteristics - separately and in combination(s), in different settings, samples, and animal types, whether/when confounded by concurrent infection(s), yield by test/combination, parallel or series interpretation, economic cost versus epidemiological benefit.

• Time to develop new or improved diagnostics

  Time to develop (lab and models) and validate (RCTs in field) improved diagnostic tests will be considerable.

• Cost of developing new or improved diagnostics and their validation

  High.

  GAPS :

  Requires experimental studies, followed by sufficiently powered and replicated trials, ideally RCTs.Access and funding to analyse large sample/datasets are both significant obstacles to independent validation exercises.

• Research requirements for new or improved diagnostics

  Populations are likely to have cases at various disease stages, which complicates diagnosis. Due to active surveillance mammalian TB is probably detected earlier than (symptomatic) human TB, so diagnostic solutions are not necessarily transferable.

  Better understanding of the host/pathogen interactions and the cellular immune response to infection by M. bovis should help defining:

  • better surrogate markers of infections; for example, multiplexing (cytokines, or cytokines combined with serology).
  • further antigens that elicit an important immune response among all infected animals but that are absent from other mycobacteria and from antigens potentially used in vaccines (DIVA tests).
  • better diagnosis for live animals applicable to non-bovines (e.g. goats, SACs).
  • stage-specific (latency versus active disease, if these are shown to be meaningful phenotypes in mammalian TB) antigens in cattle.
  • non-immunological biomarkers i.e., via epigenetics, transcriptomics, metabolomics, proteomics.
  • biomarkers of vaccine efficacy to aid DIVA.
  • need relevant BSL-contained in vitro models (tissue/organoids etc.), in vivo models (small animals, ferrets, guinea pigs etc.), BSL-contained large animal models.
  • mathematical models.

  GAPS :

  Advanced statistical and mathematical modeling required -latent class analyses etc. – assuming no gold standard, meta-analysis of test performance.Need to understand better current TB test performance characteristics - separately and in combination(s), in different settings, samples, and animal types, whether/when confounded by concurrent infection(s), yield by test/combination, economic cost versus epidemiological benefit.

• Technology to determine virus freedom in animals

  In human TB pathogenesis and epidemiology, evidence is consistent with approximately 25% of the global population being, or having been, infected with M. tuberculosis; ~10% develop active TB during their lifetime, mostly within 18 months, the remainder are allegedly latently infected with M. tuberculosis and remain a potential reservoir for reactivation, especially if immunosuppressed.

  This view is being challenged (and counterchallenged); while clearly exposed i.e., infected now or in the past, a proportion are believed to have “cleared” infection, via innate or adaptive immunity, and are not considered infectious. WHO has revised its terminology to “one-quarter of the world’s population has been infected with M. tuberculosis…” with an increasing acknowledgement of infection clearance. https://www.who.int/publications/i/item/9789240083851

  Whether a similar situation holds for M. bovis in cattle, or other animals, remains to be demonstrated empirically. Unlike human TB, official active and passive surveillance tests are widely applied; even so, a substantial number (~33%) of diseased cases are disclosed at slaughterhouse inspection in official test-negative cattle in some territories.

  GAPS :

  Disease trajectory/states remain poorly understood, for example, when an animal is infectious or has contained infection.Unknown to what extent disease states proposed for humans exist in cattle, and other animals. Tests are required which will enable definition of the true infection or disease status of a herd or animal. Relationship between diagnostic status and infectiousness is not known.

  Additional research to evaluate stages of infection in different host species and relevant biomarkers of infection stages, including infection clearance.Research to investigate theoretical immunological checkpoints, to characterise disease trajectory and phenotypes, and develop our understanding, for example, of IGRA responders. Validity of this human framework for mammalian TB needs to be investigated.

• New developments for vaccines

• Requirements for vaccines development / main characteristics for improved vaccines

  Difficulty in defining “protective immunity” against M. bovis. An immune response capable of controlling the growth of pathogenic mycobacteria is increasingly understood but characteristics of the immune response that eliminate the bacteria from the host are not well understood.Immunological correlates of vaccine efficacy and protection need to be defined and those already highlighted need to be validated.However, vaccines and vaccination strategies require evaluation under field RCT conditions.Non-sensitising vaccines would overcome the problem of skin test sensitisation associated with BCG-based strategies.DIVA tests for cattle are required should BCG vaccination be deployed.

  GAPS :

  As with M. tuberculosis vaccine R&D, not clear what “correlates of protection” are.There is a concerted international effort to identify and evaluate candidate vaccines for use in cattle and to define vaccination strategies that will reduce susceptibility in animal populations.Candidates will likely be adjuvanted BCG, modified BCG (knock-in, knock-out), characterised auxotroph, virus-vectored, or subunits.DNA, protein, and genetically modified vaccines inoculated in a single dose, given as prime-boost, or injected concurrently, which will elicit significant protection against challenge with M. bovis under controlled conditions need to be investigated further.

• Time to develop new or improved vaccines

  Work has continued in this area for several years. It was always probable that the time required for the development and evaluation/validation of a new vaccine would take many years. An estimate of 10 years is not unreasonable.BCG is already licensed in the UK for badgers, and work on BCG licensing for cattle is ongoing. BCG has shown efficacy in recent field trials in Ethiopia i.e., 39% vaccine efficacy (“end point” efficacy”, as traditionally measured), and an estimated (via mathematical modelling) direct 58% and indirect (74%) “transmission rate efficacy”.Field trials continue in the UK to test the safety of BCG and the effectiveness of BCG and DIVA testing in cattle, prior to seeking licensing. The mammalian TB science community collaborates closely with the human TB science (vaccine) community and does consider opportunities for translational benefits from trials of novel TB vaccine candidates.

  GAPS :

  Consolidated roadmap/pipeline for vaccine development (as exists for human TB) would help prioritise promising strategies as well as in the mobilisation of resource/sample sets and to ensure independent analysis of RCTs and other trial designs.

• Cost of developing new or improved vaccines and their validation

  Very high. For example, allegedly, to 2018 DEFRA (UK) invested ~£40M in cattle vaccine and DIVA test R&D.

• Research requirements for new or improved vaccines

  • Detailed investigations into the host/pathogen interactions to understand the relationships between bovis and cellular/humoral responses to infection.
  • Detailed understanding of pathogenesis and epidemiology of bovis infections in cattle herds to enable strategies to be developed for the use of new vaccines when available.
  • Development of new delivery systems for application to wildlife based on new technologies.
  • Correlates of vaccine efficacy and protection.
  • DIVA development and validation.
  • Mathematical models.

• New developments for pharmaceuticals

• Requirements for pharmaceuticals development

  Not applicable currently.

• Time to develop new or improved pharmaceuticals

  Not applicable currently.

• Cost of developing new or improved pharmaceuticals and their validation

  Not applicable currently.

• Research requirements for new or improved pharmaceuticals

  Not applicable currently.

Disease details

• Description and characteristics

• Pathogen

  Mammalian TB is a costly One Health challenge with a notoriously complex epidemiology involving livestock, wildlife, humans, and the environment. It remains a serious zoonotic risk in some countries and an occupational zoonosis, even in countries with well-developed control programme. Progress in mammalian TB control and eradication requires new data, analyses, methods, and multidisciplinary collaboration.

  More than 190 “species” of mycobacteria have been identified, mostly by traditional phenotypic methods, and their taxonomy is constantly being revised in the genomics era. Most “non-tuberculosis mycobacteria” (NTMs) are fast-growing environmental saprophytes or occasional opportunistic pathogens; some mycobacterial “species” are significant pathogens of humans and other animals.

  TB in animals (mammals) is caused by various members of the Mycobacterium tuberculosis Complex (MTBC), a highly genetically related group of mycobacteria of the family Mycobacteriaceae, which show striking host-adaptation and phylogeography by lineage. M. tuberculosis sensu stricto has been a major killer throughout human history and, although in principle avoidable and treatable, remains a leading global cause of infectious disease death in humans. Risk factors include socioeconomic metrics, malnutrition, communicable and non-communicable comorbidities etc. Current dogma suggests that ~25% of the global human population is, or has been, infected with M. tuberculosis.

  A nested set of genetic tests has been developed which resolves the MTBC at different evolutionary and geographical scales into lineages, clones, and sequence types. The MTBC comprises currently nine human-adapted lineages, which have different distributions and pathogenesis, and at least nine animal-adapted lineages. Mammalian TB in Bovidae is caused mostly by M. bovis, but M. orygis is being increasingly recognised as a bovine pathogen in South Asia. There are other animal host-adapted ecotypes (ecovars); M. caprae is host-adapted to goats, M. microti is host-adapted to small rodents etc., although some rare spillover events are described.

  A suggestion to rename M. bovis as M. tuberculosis var. bovis has been implemented in some areas; the use of M. bovis as a heterotypic synonym should avoid confusion. M. bovis is unusual in the MTBC in that it can infect a relatively wide range of mammalian hosts and can cause human TB through zoonotic transmission.

  M. tuberculosis is paradigmatic of an airborne infectious disease; most transmission is “direct”, via aerosols in shared and often poorly ventilated airspaces. It would be reasonable to assume that M. bovis shares many of these properties. M. bovis can transmit via contaminated food products, but also via air from infected animals to humans, but rarely from human to human, unless immunocompromised.https://www.who.int/publications/m/item/global-technical-consultation-report-on-proposed-terminology-for-pathogens-that-transmit-through-the-air.

  Of emerging concern is another MTBC member, M. orygis, which is the predominant cause of mammalian TB in Bos indicus cattle in the Indian sub-continent. Links to human cases in south Asia have led to a reassessment of its importance as a zoonotic agent alongside M. bovis: a Western centric approach to zoonotic TB (zTB) may have underappreciated this agent.

  GAPS :

  Mammalian TB prevalence in cattle is well recorded in most European countries. However, although several studies have been performed in other livestock and wildlife (goats Spain, pigs Italy, badgers UK, badger ROI, wild boar Spain and Portugal, deer central Europe, wildlife France and Northern Italy), information is still missing in Europe on the distribution of infection by M. bovis, M. caprae, M. pinnipedii and even M. tuberculosis in other animal species.

  Distribution of mammalian TB, as well as infection by the other mycobacteria referred previously, is poorly characterized in developing countries.

• Variability of the disease

  Extant host-adapted members of the MTBC are fully clonal. There are remarkable consequences to being a clonal pathogen; there is no reason to expect these pathogens to neatly form species, and they are particularly susceptible to severe reductions in population size/diversity due to population bottlenecking or selective sweeps (periodic selection). Test and cull policies in some territories will have bottlenecked and purged variation in the pathogen population. Whether the bacteria that emerged from such bottlenecks had some selective advantage or different phenotype is being investigated; the null hypothesis is that this seems unlikely. A nested set of genetic tests has been developed, which resolves the MTBC at different evolutionary and geographical scales into lineages, clones, and sequence types. The MTBC comprises currently nine human-adapted lineages, which have different distributions and pathogenesis, and at least nine animal-adapted lineages sharing highly conserved genomes, differing by ~2,000 single nucleotide polymorphisms (SNPs), and with no significant signal of genetic exchange between extant members. The global distribution of M. bovis clones largely reflects the historic trading routes between various countries and former colonies/dependencies.

  Modern MTBC members are exceptionally clonal and diversify locally via point mutation (SNPs), minisatellite variation, insertion sequence (IS)- and CRISPR-mediated deletions, InDels, and other such structural mechanisms. Research to investigate whether pathogen epigenetics contributes to M. bovis phenotypes is ongoing. The substitution rate has been estimated in several longitudinal studies and is exceptionally slow at ~0.3-0.5 substitutions per genome per year. The M. bovis genome (4.3Mb) is slightly smaller than the M. tuberculosis genome, although they have evolved from a common ancestor.

  A striking and consistent finding in several studies/territories has been the geographical localisation of M. bovis types at various scales via founder effects and clonal expansion. Such structured molecular surveillance, methods and data have essentially two applications: (1) to investigate important aspects of mammalian TB epidemiology – transmission dynamics, phenotypes (pathophysiology) using descriptive, analytical and disease modelling studies, and (2) to inform outbreak investigations, case studies and contact tracings (microbial forensics = test-and-trace, risk pathway assessment). Cattle and wildlife tend to share the same types at regional- and farm-level, which is consistent with a shared epidemic and wide host range.

  Molecular epidemiology has improved the understanding of M. bovis population structure and pathogen maintenance and spread. However, it is increasingly being replaced by genomic epidemiology, exploiting recent developments in whole-genome sequencing and bioinformatics to facilitate more detailed studies on M. bovis transmission dynamics, phylogenetics, and evolution.

  The natural history of MTBC disease is a spectrum of disease states. The outcome of infection is variable and will be influenced by environmental (non-genetic) host factors (concurrent infection, nutrition, stress, pregnancy, herd hierarchy, connectivity, etc.), genetic host factors (genetic immunity), pathogen variation, and force of infection. The role of host microbiome(s), which exist in the lungs, rumen etc. are probably underappreciated and under researched. For optimal response to diagnostics and vaccination, it is important that animals are in good health and energy balance.

  GAPS :

  Whether, and at what genetic or geographical scale, genotype differences are associated with phenotypes remains to be determined empirically.Research to investigate whether host-adapted MTBC variants epigenetics is associated with different phenotypes.Scope to investigate the role of host microbiome(s) in host mammalian TB phenotypes.

• Stability of the agent/pathogen in the environment

  While seemingly a fundamental question, the relative importance of “direct” versus “indirect” transmission of M. bovis in various epi-systems is not settled and is not straightforward to investigate. M. tuberculosis is paradigmatic of an airborne respiratory infectious disease, and we expect M. bovis to be similar. However, although probably context dependent, there is evidence (PCR and metagenomic detections) for some level of environmental M. bovis survival, which might constitute a short-lived environmental source capable of contributing to indirect intra- and inter-species transmission. Simulated micro- and mesocosms have been developed to investigate these interactions experimentally. Some recent, advanced, multi-host mathematical models explain the observed data better when allowing for environmental transmission and are consistent with a transient M. bovis environmental half-life of ~6 months. Further support for an indirect interspecies transmission route via the environment comes from the finding that, in Britain and Ireland, the main wildlife host, the European badger, has been empirically shown, via proximity logger collars, not to come into regular, close direct contact with cattle. Whether an M. bovis-contaminated environment can be rendered into an infectious aerosol by inhalation or ingestion remains to be demonstrated. M. bovis can survive in cattle slurry but recently published PCR-based studies suggest that this is unlikely to be of major epidemiological importance. Experimental evidence suggests that MTBC pathogens can sense and adapt to changing environments. It would be reasonable to assume M. bovis will exhibit such characteristics.

  GAPS :

  Incomplete information on agent maintenance in the environment, including infected carcasses, as a viable pathogen representing a real source of infection to livestock and wildlife.

• Species involved

• Animal infected/carrier/disease

  Within the MTBC, M. bovis has a relatively wide host range in mammals, including humans, various livestock, wildlife, and companion animals; its major host-adaption and most frequent host is cattle. Wildlife represents a serious problem in several countries worldwide as maintenance and/or spill over species and/or reservoirs of mammalian TB.

  As in M. tuberculosis in humans, we expect a spectrum of disease stages post infection, including some level of asymptomatic infection and transmission, which makes control extremely difficult; the epidemic is largely unobserved (cryptic), resulting in apparent prevalence significantly underestimating true prevalence in all hosts. There is relatively structured and intense surveillance of livestock in many countries and some level of wildlife surveillance. Current official tests on livestock can detect past or current infection; the extent to which such cases are infectious remains to be determined empirically; the precautionary principle dictates that they be removed as high risk. There is some molecular epidemiology evidence of long-term productive infection in cattle, which often pass one or several official tests.

  The definition of host species as true réservoirs, spillover hosts, or dead-end hosts is probably context dependent but is epidemiologically and ecologically important, and needs to be determined empirically. Ecology plays a key role in determining host status – for example, host density in the environment will modulate number of infectious contacts.

  GAPS :

  Gap in understanding the full spectrum of mammalian TB infection, immune responses, transmission, and disease in livestock and wildlife and how these can relate to infectivity.Disease progression can be distinct in different affected species. Existence and consequences of latency unresolved.Similarly determining empirical evidence that can unravel the role that ecological factors can play in determining what type of host (maintenance/spillover) wildlife species may be in different contexts is needed.

• Human infected/disease

  M. bovis is historically a recognised cause of zoonotic TB (zTB) in humans, accounting for 10-30% of TB deaths in humans in the USA and Europe in the early 1900s; most TB cases in humans are caused by M. tuberculosis. TB screening in humans is mostly targeted at respiratory disease (most TB cases by M. tuberculosis are pulmonary) while M. bovis in humans tends to be extra-pulmonary. Human disease caused by M. bovis is now rare in countries with successful mammalian TB control and eradication programmes, established meat inspection procedures, human BCG vaccination, and milk pasteurisation. However, lack of differentiation between M. tuberculosis and M. bovis may occur, even in Europe, leading to under ascertainment of TB caused by M. bovis in humans. In countries where mammalian TB is poorly controlled in livestock, and where consumption of raw milk or unpasteurised dairy products is frequent, mammalian TB may represent an important human health risk, which has been prioritised by WHO. https://www.who.int/teams/global-tuberculosis-programmeme/zoonotic-tbhttps://www.who.int/teams/global-tuberculosis-programmeme/zoonotic-tb

  In South Asia, M. orygis has emerged as an important cause of mammalian TB in indicine cattle with links to zoonotic cases. With an estimated 21.8 million affected animals in India alone, high densities of human and animal hosts, consumption of unpasteurised dairy products, cultural differences regarding farming cattle and poor disease control infrastructure, infection with M. orygis may be one of the pre-eminent causes of zTB in India but is currently underestimated.

  GAPS :

  Information on the incidence/prevalence of zoonotic TB in humans is sparse, especially in countries with no mammalian TB control/eradication programmes and/or poor food control systems.

  Expanding surveillance and molecular tests to detect, characterise and scope the extent of M. orygis infection in cattle and humans requires considerable effort.

• Vector cyclical/non-cyclical

  Insect vectors are not considered to be significant in M. bovis epidemiology. Infected livestock, wildlife, companion animals, and humans could be classified as mammalian TB vectors in the sense that they represent living agents that carry and transmit pathogens to other susceptible living agents.

• Reservoir (animal, environment)

  Well documented reservoirs in wildlife exist in several territories and render complete eradication difficult. The potential host range comprises any of the free-ranging mammal species, but the host status of these species is variable. Some are too restricted in numbers or distribution to have any significant role in disease dynamics; others exhibit limited susceptibility or are dead end hosts that become infected but not infectious. Controversy has arisen over the distinction between two categories of infectious host: spillover hosts that require an external source of re-infection to maintain the disease within their population, and reservoir hosts, where the disease persists by cycling within the population.

  An understanding of the potential of each wild animal species as a reservoir of infection for domestic animals is reached by determining the nature of the disease in each wild animal species, the routes of infection for domestic species and the risk of domestic animals encountering an infectious dose. The mere presence of infection in a wild animal population does not by itself provide evidence of a significant wildlife reservoir. Relevant factors include infection routes, anatomical location of lesions and infection, level and routes of elimination, routes of potential transmission to domestic animals, and knowledge of minimal dose for infection.

  Species considered maintenance hosts are brush–tailed possums in New Zealand; badgers in the UK and Ireland; bison and elk in Canada; kudu and African buffalo in southern Africa; wild boar and red deer in the Iberian Peninsula.

  White-tailed deer in the USA (Michigan) are considered maintenance hosts. However, some authors believe this species may be a spillover host that maintains the organism only when its population density is high. Probably the same applies to red deer and wild boar on the Iberian Peninsula. The infected host can serve as a maintenance or spillover host depending on the local epidemiology (spatial and temporal). Species reported to be spillover hosts include sheep, horse, pig, dog, cat, ferret, camel, llama, alpaca, many species of wild ruminants including deer and elk; elephant, rhinoceros, fox, coyote, mink, primate, opossum, otters, seal, sea lion, hare, raccoon, bear, warthog, large cats (including lion, tiger, leopard, cheetah and lynx), wolves and several species of rodents.

  In South American camelids the natural mammalian TB burden is largely unknown. Infection occurs mainly via the respiratory route. Infection tends to be more common when animals are intensively managed.

  GAPS :

  Information on wildlife susceptible to mammalian TB in Europe is relatively well documented. Role of each species and distribution of infected animals needs to be clarified in some countries.

  Maintenance and spill over hosts vary by territory and context. Clear definition of maintenance and spill over species missing for the most part. This may not be easy and depends on ecological contexts; determining such contexts is key to understanding the precise roles of potential reservoirs.

• Description of infection & disease in natural hosts

• Transmissibility

  Many of the epidemiological parameters of local mammalian TB epidemics are highly over-dispersed (skewed); the Pareto Principle (the 80:20 rule) often applies. For example, in some territories, 20% of herds contain 80% of mammalian TB cases; 80% of movements are recorded in 20% of herds etc. Although mammalian TB epi-systems are complex and “noisy”, it is biologically plausible that super-spreading is a feature.

  While likely to be context dependent, and predictably host density dependent, consensus from a series of recent whole-genome sequencing-based phylodynamic studies of various multi-host epi-systems is that most transmission occurs in the “within-host” intraspecies compartment, especially the cattle-cattle compartment; signals of interspecies transitions (effectively transmissions) are significantly smaller. This too is context dependent; studies in M. bovis endemic areas in South Africa have shown significant interspecies transmission. There is evidence of spillover/spillback involving local infectious wildlife in several studies. The opportunities for extensive cattle-to-cattle transmission presented by current farming practices are consistent with this small inter-species spillback being “amplified” within herd. Close contact and high host density seem to be important factors that promote or sustain transmission of mammalian TB. In countries without disease control, cattle-to-cattle transmission rates can be high, particularly when animals are kept under high-intensity/density husbandry.

  Mathematical models of intra- or inter-species transmission have been parameterised to simulate a few host-pathogen systems (possum-cattle in New Zealand, badger-cattle in the UK, deer-cattle in North America and wild boar-red deer-cattle in France). RCTs tend to be prohibitively expensive; mathematical models have been useful.

  The host-adapted nature of M. bovis is consistent with the observation that it tends not to transmit well between humans, except where those exposed were immunocompromised.

  The role of the environment and pathogen survival in various matrices in modulating transmission needs to be assessed. It may only be a transient risk that requires replenishment from infected livestock and wildlife, but if indirect transmission routes are common, as they appear to be in the cattle-badger epi-system observed in Britain and Ireland, it will be important to account for impact and duration if infected hosts are removed.

  In support of classical epidemiological studies, the ability to generate and analyse M. bovis whole-genome sequences, supported by bioinformatics developments, has significantly improved the information content, resolution, and functionality of molecular epidemiology. This has enabled phylogenetic and phylodynamic analyses of transmission dynamics within (intraspecies) and between (interspecies) livestock and wildlife populations in several territories.

  GAPS :

  What risk factors affect cattle-cattle transmission?

  Genetic or geographical scale at which distinct pathogen molecular types might vary in transmissibility largely unknown; we hypothesise that local scale pathogen variations will have neutral impact on phenotype.

  Models of wildlife to domestic animal transmission are lacking for most host-pathogen systems.

  Investigate the existence and impact of super-spreading.

  Investigating the role that differing ecological contexts (host (s) density, shared geographic range, and numbers of infectious contacts) can play in modulating transmission important to assess.

• Pathogenic life cycle stages

  Mammalian TB doesn’t exhibit lifecycle stages as would be understood for example in parasitology. Although context dependent, there is evidence (PCR and metagenomic detections) for some level of environmental survival, which might constitute a transient environmental source capable of contributing to indirect intra- and inter-species transmission. Some recent, advanced, multi-host mathematical models explain the observed data better when allowing for environmental transmission. Experimental evidence indicates that M. tuberculosis senses and adapts to changing environments, and similar systems are active in M. bovis.

  GAPS :

  Role of shared and potentially contaminated environment under-researched.

• Signs/Morbidity

  Mammalian TB signs and morbidity vary greatly between mammal species and territories and are influenced by the extent of official controls and interventions. For example, in territories with well-developed official control programme clinical signs are rarely, if ever, seen. This implies that asymptomatic and undiagnosed infection and transmission must be a feature of such local epidemics, which are largely “unobserved”. Even in such territories clinical signs are evident at postmortem carcase inspection, in official test reactor positive and negative cattle. The hallmark lesion of M. bovis infection, at least in cattle, is the granuloma, histologically defined as an organised mass of different effector and immune cells that coalesces at the site of infection. Whether granuloma production is to the benefit of the host and/or the pathogen remains to be settled.

  Individual or clustered granuloma (tuberculoma) tend to be found in the head, lungs and draining lymph nodes. MTBC organisms are believed to disseminate through the body, mostly via the lymphatic system. Human TB is proposed to be a disease of the lymphatic system, with the lungs acting as an entry and exit portal. On rare occasions in official livestock programmes, generalised mammalian TB is identified in multiple organ groups; such cases would be condemned. Otherwise, carcases are processed for the human food chain.

  In territories with less well-developed control, late stages of mammalian TB generate clinical signs; common symptoms include progressive emaciation, a low–grade fluctuating fever, weakness, and lack of appetite. Animals with pulmonary involvement usually have a moist cough that is worse in the morning, during cold weather or exercise, and may have dyspnoea or tachypnoea. In the terminal stages, animals may become extremely emaciated and develop obvious respiratory distress. In some animals, the retropharyngeal or other lymph nodes enlarge and may rupture and drain. Greatly enlarged lymph nodes can also obstruct blood vessels, airways, or the digestive tract. If the digestive tract is involved, intermittent diarrhoea and constipation may be present.

  In cervids, mammalian TB may be a sub-acute or chronic disease, and the rate of progression is variable. In some animals, the only symptom may be abscesses in isolated lymph nodes, and symptoms may not develop for several years. In other cases, the disease may be disseminated, with a rapid, fulminating course.

  In cats, disease seems to evolve more rapidly than in cattle and the symptoms may include weight loss, a persistent or fluctuating low-grade fever, dehydration, decreased appetite and possibly episodes of vomiting or diarrhoea.

  In brush-tailed opossums, mammalian TB is often a lethal pulmonary disease that typically lasts two to six months. In the final stages of the disease, animals become disoriented, cannot climb, and may be seen wandering about in daylight.

  Passive surveillance, in the form of road traffic accident surveys of badgers are used to estimate apparent and true prevalence. A significant proportion of infected badgers have no visible lesions and can survive for many years. In symptomatic badgers, mammalian TB is primarily a respiratory disease.

  Primates develop necro granulomatous pneumonia: these animals may show behaviour signs like depressive-like behaviour and the animals tend to be solitary.

  Lesions in brushtail possum and badgers have little or no fibrosis, and mineralisation is very rarely observed. The macroscopic appearance may resemble pyogenic abscesses. Badgers also can show open wounds and behaviour changes. Elbow hygroma with associated lameness may be observed in lions. They might also show chorneal opacity, skin wounds, and poor cicatrization. Swollen head nodes with draining fistulae are almost pathognomonic in greater kudu. African buffalo present in progressive emaciation ; lesions mimic those observed in cattle.

  Information is still scarce on disease progression in SACs in natural habitats (severe disease but can be asymptomatic shortly before animals die). Mammalian TB can be difficult to diagnose in SACs, based solely on clinical examination but should be considered in cases of chronic loss of appetite/condition and debilitating disease, with or without respiratory signs. Chronic cough and enlarged lymph nodes can be indicative of mammalian TB in camelids, especially if failing to respond to antibiotics for respiratory infection.

  GAPS :

  Investigation of whether disease or advanced pathology is a pre-requisite for transmission. Can less obvious, or no, pathophysiology seed infection? Is transmission from the latter cases quantitatively different? Is excretion/relative infectivity correlated with diagnostic test results?

• Incubation period

  The natural history of MTBC disease is a spectrum of disease states; severity will be contingent on innate immunity, immunological memory and pathogenic load. The outcome of M. bovis infection is variable and will be influenced by environmental (non-genetic) host factors (concurrent infection, nutrition, stress, pregnancy, hierarchy, connectivity, etc.), genetic host factors (genetic immunity), pathogen variation, and force of infection (dose). Risk factors in cattle studies tend to be context dependent; however, herd size, which can be a proxy for other measures, and some wildlife-associated metrics, appear consistently. For optimal response to diagnostics, it is important that animals are in good health and energy balance.

  Incubation periods (in this case time to detection) in some animal experimental models have been estimated and are likely to be dose- and context-dependent and highly variable. Figures in the order of 6-20 months have been reported; some studies estimate 1-2 months. The skin test and IGRA will pick up most infected animals long before 6 months. Advanced within-host mathematical models, parameterised with experimental and/or field data, are increasingly able to estimate these important epidemiological parameters. While it would be unwise to extrapolate and generalise, such estimates are useful in attempts to identify when and where transmissions are occurring. It is known that in experimental infection, pathology (but not clinical symptoms) can develop within weeks upon infection (known for several species that were experimentally infected and even for young calves).

  For other livestock, wildlife and companion animals, precise information is largely missing but it is accepted that upon infection, animals, depending on the species, may or may not develop signs of disease.

  GAPS :

  Incubation period modelled to be long for cattle, but clear information lacking for most other affected animal species.

• Mortality

  Relative mortality is highly variable across host species and subject to many factors. In countries with cattle control programmes, mammalian TB is often, but importantly not always, confined to a limited number of animals per herd and most reactors are detected during routine testing. Consequently, direct mortality from mammalian TB in such systems is rare.

  Various animals differ significantly in their response to infection; although this response will be highly variable due to the multi-factorial nature of mammalian TB; some tend to be highly susceptible to progressive disease i.e., brush-tail possums in NZ.

  Mortality due to mammalian TB, where disease is uncontrolled and allowed to progress, has been clearly reported in a few wildlife species, for example, buffalos and lions in the Kruger National Park in South Africa, but the overall picture is incomplete.

  GAPS :

  Information largely missing on mortality due to mammalian TB in species other than cattle.

• Shedding kinetic patterns

  Sporadic shedding of M. bovis by cattle has been mostly associated with respiratory secretions, although bacteria might also be present in faeces and milk, and to a lesser extent shedding has been described in urine, vaginal secretions, or semen. Large numbers of organisms may be shed in the late stages of infection. Using conventional culture and PCR-based tests, M. bovis was not detected in slurry from TB-positive herds in a recently published UK study.

  Under experimental infection conditions, shedding in cattle is sporadic and intermittent and with low bacillary loads (nasal secretions). However, sporadic shedding can occur early post-infection and in the absence of visible signs. Sensitive and reproducible methods (e.g. Madison chamber, air filtration etc.) and PCR-based tools to detect such shedding are probably suboptimal, with the result that shedding risk is probably underestimated.

  Badgers can similarly shed M. bovis from various bodily secretions and their use of latrines and territorial marking may represent a risk to cattle exposure at pasture. Badgers with advanced generalised disease excrete from the respiratory tract, in urine if renal lesions have developed, in faeces if infected respiratory excretions are swallowed, and from bite wound exudates.

  Experimentally infected white-tailed deer shed by the nasal, and faecal-oral routes; shedding can occur intermittently a few weeks after experimental infection. In field settings, white-tailed deer contamination of supplementary winter feed posed a risk to local cattle.

  GAPS :

  Shedding routes to be determined for most species. More precise information required for cattle.Methods with increased sensitivity to detect mycobacteria or their components (DNA, bacterial cell wall lipids or others) in faeces and other biological samples necessary.

  Research to investigate cattle-wildlife interactions at pasture, for example, cameras, GPS, or proximity collars to investigate the risk at wildlife latrines.Recent developments with airborne detection of excretion in human TB might be relevant.

• Mechanism of pathogenicity

  M. bovis is a facultative intracellular pathogen. Within the host it infects mainly macrophages and dendritic cells. The most relevant virulence factor is its ability to resist the bacteriocidal mechanisms of these professional immune cells.

  Pathology is largely caused by the host inflammatory immune responses towards the pathogen. In cattle and several other species, the immune response against M. bovis leads to the formation of granulomas. The progressive evolution of granulomas with central necrosis and caseation surrounded by fibrotic tissue. These coalescing lesions lead to the progressive destruction of the affected organs and provides a mechanism for pathogen transmission. Ingestion is the primary route of infection in carnivores/scavengers and may result in initial GI-related disease that may progress to pulmonary or systemic TB. The natural history of MTBC disease is a spectrum of disease states. The outcome of M. bovis infection is variable and will be influenced by environmental (non-genetic) host factors (concurrent infection, nutrition, stress, pregnancy, hierarchy, connectivity, etc.), genetic host factors (genetic immunity), pathogen variation, and force of infection (dose).

  As with human TB, current diagnostics detect “exposure” i.e. current or past infection. Comparative pathology would predict the existence of compartments of animals that have “cleared” infection via innate mechanisms (exposed but test negative), those that have cleared infection by acquired immunity (exposed and probably test positive) and those that are infected and diseased (probably test positive). Even in territories with developed control programmes, a substantial amount of infection is disclosed in official test-negative cattle. Testing algorithms are currently unable to identify or quantify these various compartments and the precautionary principle refers; infected animals should be removed.

  GAPS :

  Key challenge: knowledge required about disease stages, progression, and phenotypes in different species to understand the mechanisms of pathogenicity. Evaluation of location and structure of lesions might provide important information.

  Studies on immune response against mycobacteria in different species should also provide important knowledge on pathogenesis, which is an essential component for the development of better diagnostic tools and control measures such as vaccines.

• Zoonotic potential

• Reported incidence in humans

  While human infections with zTB are relatively rare in more developed nations, due to implementation of mammalian TB control/eradication programmes and reduced consumption of unpasteurized dairy products, less is known about the risk in the developing world. From those countries, where information is available, M. bovis accounts for a percentage of human TB cases, ranging from 0.4 to 8%, showing that M. bovis is an important, although probably under ascertained factor in the human TB epidemic.

  Various estimates exist; one estimates global zTB prevalence to be 3.1% of all human TB cases, accounting for 2.1% and 9.4% of pulmonary and extra-pulmonary TB cases, respectively.

  Estimates of the global burden of zTB in humans are imprecise; WHO (2016) estimated 147,000 new cases of zTB in humans (~1.4% total human TB burden), and 12,500 deaths annually.

  Although rare, reverse zoonoses (M. tuberculosis in animals) have also been reported in Europe, China, India, and Ethiopia). How this contributes to human disease is still unknown.

  zTB tends to be extra-pulmonary, and most studies of TB in humans are based on sputum diagnostics. If special care on the microbiological culture conditions is not taken, it is possible to miss infection by M. bovis or misdiagnose a M. bovis infection as M. tuberculosis infection (optimal culture protocols are not the same for M. bovis and M. tuberculosis; some reference labs are unable to distinguish).

  South Asia yields ~37% of all human TB cases; recent evidence suggests that M. orygis causes zTB in South Asia.

  GAPS :

  Knowledge about the prevalence of TB caused by M. bovis (pulmonary and extra-pulmonary) in humans in developing countries is missing for the most part. General lack of capacity and resources to distinguish M. bovis from M. tuberculosis; essential to understand the reverse zoonotic relevance of M. tuberculosis infection in cattle.More research (data) required to substantiate role of M. orygis.

• Risk of occurence in humans, populations at risk, specific risk factors

  M. bovis can infect humans, primarily by the ingestion of unpasteurized milk and dairy products but also by aerosols and through breaks in the skin. People living in developing countries, where no or weak mammalian TB control/eradication programmes exist, are at particular risk, especially when living a pastoral lifestyle, and where consumption of unpasteurised milk and dairy products is common. Infection with HIV increases the susceptibility to mycobacterial infections.

  In Africa, 80% of the population is estimated to be rural and to depend solely on livestock for food and wealth and 85% of the cattle, as well as 82% of the people, live where mammalian TB is only partially controlled, if at all. A specific risk factor for children is that 90% of the total milk produced in Africa is consumed raw or soured.

  zTB is an important issue in countries where no/limited mammalian TB control programmes are implemented and is potentially even more relevant in countries where the rural populations represent a high percentage of the total population. Humans can also acquire zTB by direct contact with infected livestock, wild and companion animals. Specific groups at risk of this occupational zoonosis are farmers, hunters, abattoirs workers, and veterinarians. Infection can occur through the respiratory route or through punctures in the skin. Although notifiable in many countries, there can be a lack of coordination between animal and public health authorities.

  GAPS :

  Gap in structured surveillance of lifestyle and occupational exposure.

• Symptoms described in humans

  zTB is largely indistinguishable from classical M. tuberculosis in humans, considering clinical, radiological, and pathological features. TB due to M. tuberculosis is mostly pulmonary (aerosol infection); zTB tends to be extra-pulmonary (cervical lymphadenopathy, gastro-intestinal). Pulmonary TB due to M. bovis is considered rare (although possibly under-diagnosed in developing countries), with most cases confined to rural areas. Before the advent of pasteurisation, M. bovis infection was common in children. TB symptoms, for most cases, are non-specific, such as moderate fever, fatigue, weight loss and night sweats. Depending on the organ(s) most affected, cases might present cough (pulmonary TB) or lymphadenopathy (zTB) and diverse digestive problems (gastro-intestinal TB). Gastrointestinal TB is a major health problem in many developing countries. A recent, significant increase has occurred in developed countries, especially in association with HIV infection.

• Likelihood of spread in humans

  Reflecting the host-adaptation of M. bovis largely to cattle, person-to-person transmission of zTB seems to be a rare occurrence. However, M. bovis has occasionally been transmitted within small clusters of immunosuppressed individuals.

• Impact on animal welfare and biodiversity

• Both disease and prevention/control measures related

  Mammalian TB poses a serious wildlife conservation and welfare problem and is a particularly serious problem for wildlife conservation, for example, in the Kruger National Park in South Africa, where the geographical spread of the disease has been reported in buffaloes, with incidental spread to other animal species living in the parks, including kudu, baboons, lions, cheetah, leopards, rhinoceros, and elephants. In Uganda, mammalian TB has been reported in the Queen Elizabeth National Park since the late 1960s and has been confirmed in buffaloes in the Kadepo Valley National Park. In Zambia, mammalian TB has been identified for several years in Red Lechwe on the Kafue flats. Transmission to herds of wildebeest was confirmed for the first time in 1998.

  In Europe, mammalian TB has been a significant infectious cause of death in the critically endangered Iberian Lynx.

  In the USA the outbreak of mammalian TB in white-tailed deer in Michigan continues to pose problems; the disease has been transmitted to coyotes, red foxes, racoons, black bears, and bobcat in that multi-host epi-system. Attempts are under way to combat the disease in cervids by reducing their population density and by prohibiting supplementary feeding of deer by humans. In Minnesota, an outbreak of mammalian TB in cattle and white-tailed deer was controlled by aggressive efforts to reduce deer densities including liberalized hunting and sharpshooting and a ban on feeding of deer.

  In Canada, mammalian TB is endemic in a sub-population of bison, elk, and white-tailed deer. All the species affected in Michigan are abundant or superabundant; none is of conservation or biodiversity significance. In contrast, wood bison in northern Canada are of critical conservation significance.

  GAPS :

  Unknown for most countries with few exceptions and consequently measures to control are mostly unknown.Lack of structured surveillance and validated diagnostic tests for different wildlife species.

• Endangered wild species affected or not (estimation for Europe / worldwide)

  Many wildlife species are affected, but whether this has an impact on endangered species depends on the definition of endangered species (see list at . The problems in lions in Africa (e.g. Kruger National Park in South Africa) and the critically endangered African wild dog that develops fatal systemic mammalian TB, should be highlighted as well as the critically endangered Iberian lynx for which mammalian TB is considered one of the most important deadly diseases (an endangered species with extremely low numbers of individuals and patchy population density).

  GAPS :

  Unknown for most countries with few exceptions and consequently measures to control are mostly unknown.Lack of structured surveillance and validated diagnostic tests for different wildlife species.

• Slaughter necessity according to EU rules or other regions

  Control of mammalian TB based on test-and-slaughter principles has historically been successful in cattle in several territories and for some cases in wildlife. In some territories, notably with well-documented wildlife reservoirs, control and ultimate eradication remain elusive, despite the implementation of costly, comprehensive, and detailed control programme. It is, however, expected to have a limited role for the control mammalian TB in endangered free-ranging wildlife species.

  In Minnesota, the measures taken to control an outbreak of mammalian TB included >50% reduction in white-tailed deer densities by liberalized hunting and sharpshooting. In Australia, mammalian TB was eradicated from feral water buffalo by large-scale mustering and stamping out of hundreds of thousands of animals.

  In New Zealand, non-selective government-led culling of introduced brushtail possums is a central component of the campaign to control mammalian TB in cattle and farmed deer. This strategy, alongside strict industry-led controls on cattle, reduced the number of infected cattle and deer by over 60% between 1994 and 2001; progress has continued. In some parts of New Zealand, the culling of ferrets was included in the programme.

  The extent to which infected local wildlife contribute to mammalian TB in cattle is likely to be context-dependent, as are the options for effective intervention. This has been a contentious issue for several years in some territories; there is still considerable mis/disinformation and (dis)confirmation bias and it can be a polarising and toxic political debate; such policy and political decisions need to balance several competing interests and issues. Recent industry-led culls, which are not RCTs and must exist alongside a package of official mammalian TB control measures in cattle in the UK, are reported to be effective. Test and slaughter may not always be feasible, practical, or realistic in many countries; other strategies may need to be considered.

  GAPS :

  Beyond sanctioned field trials, information on the effectiveness of strategies based on culling is missing for several wildlife species.

• Geographical distribution and spread

• Current occurence/distribution

  Mammalian TB is widespread globally. Although complete eradication has proven exceedingly difficult, control programmes have eliminated, or nearly eliminated, mammalian TB from livestock in many countries. For example, the significant reduction in mammalian TB prevalence in the USA over decades is rightly hailed historically as a major achievement of veterinary science. However, in developing countries, where surveillance and control activities are inadequate or unavailable, the levels of disease remain largely unknown and estimates imprecise.

  Recent phylogenetic analyses, based on global datasets of M. bovis whole-genome sequences (WGS), are consistent with M. bovis originating in East Africa between the 3^rd and 12^th centuries AD as an MTBC ecotype (ecovar) capable of effective infection and transmission in cattle. Phylogenomics recognises at least 3 main livestock-associated (La) groups within the MTBC with La1, La2, and La3 comprising M. bovis, M. caprae, and M. orygis, respectively. M. bovis is widely dispersed, unlike M. caprae and M, orygis.

  Further analyses recognise at least 4 global lineages of M. bovis, dispersed by location rather than host. Global distribution is influenced clearly by historic import/export of cattle breeds, followed by local diversification. Past selective sweeps and population expansion after a recent bottleneck remain as major evolutionary drivers. International collaborations are advocating a more unified and portable approach to pathogen variant nomenclature than has been available to date. Geographical localisation of molecular types, at various scales, is useful for tracing mammalian TB between and within territories (phylogeography). https://www.woah.org/en/disease/bovine-tuberculosis/

  Accounting for the range of M. orygis as a recognised common cause of mammalian TB is important considering recent investigations that highlight its prevalence as a source of cattle disease in South Asia.

  GAPS :

  Distribution of the disease in cattle and wildlife is mostly unknown in most developing countries.Accounting for both M. bovis and M. orygis prevalence important given emerging importance.

• Epizootic/endemic- if epidemic frequency of outbreaks

  Mammalian TB remains endemic in several countries even with advanced and costly ongoing mammalian TB control programmes, where outbreaks (breakdowns) can be classified epidemiologically as chronic, persistent, recurrent, or sporadic.

• Speed of spatial spread during an outbreak

  Information to clearly determine the speed of spread of mammalian TB is missing or imprecise. Within an area or country, it is known to depend on contact and trading networks and the degree of connectivity between uninfected and infected animals, herds etc. Molecular epidemiology provides a means to estimate the landscape diffusion of defined types or new variants; one such study estimated diffusion from a point source, although highly variable, at ~2km per year. WGS-based molecular epidemiology illustrates the fate of M. bovis WGS types inadvertently imported into mammalian TB-free territories via cattle trade. Evidence of establishment of micro-epidemic(s) in several local herds, spillover into local wildlife, followed by spillback into cattle exists in UK data.

  After its introduction in the 1960s M. bovis spread through the entire Kruger Park (20,000km²) within ~50 years.

  Rate of spatial spread could be estimated via mathematical modelling. Phylodynamic models could also be used provided archives of systematically sampled bacterial cultures are available to build phylogenies of sufficient temporal depth.

  GAPS :

  Determination of the speed of spatial spread during outbreaks in distinct conditions is needed.

• Transboundary potential of the disease

  Mammalian TB doesn’t recognise geo-political or administrative borders and presents high transboundary potential, due to the chronic nature of the disease, well documented limited sensitivity diagnostics (where used) and the wide range of susceptible hosts, combined with insufficient border control and understaffed veterinary services, in combination with wildlife population movements and trade of animals between countries. Translocation of wildlife for conservation purposes can also be a significant threat; the Wood Buffalo National Park, in Canada, became an infected area after plains bison were translocated with disease spread contaminating cattle in neighbouring ranches.

  Mammalian TB doesn’t recognise geo-political or administrative borders and presents high transboundary potential, due to the chronic nature of the disease, well documented limited sensitivity diagnostics (where used) and the wide range of susceptible hosts, combined with insufficient border control and understaffed veterinary services, in combination with wildlife population movements and trade of animals between countries. Translocation of wildlife for conservation purposes can also be a significant threat; the Wood Buffalo National Park, in Canada, became an infected area after plains bison were translocated with disease spread contaminating cattle in neighbouring ranches.

  GAPS :

  Diagnostic tools adapted to wildlife are required for structured surveillance and transboundary outbreak investigations.Genomic tools, that can exploit the observed phylogeographic clustering of M. bovis, are a useful way to establish probable transboundary sources. Establishing wider genomic surveillance and standardised nomenclature are key to developing transboundary source tracing.

• Route of Transmission

• Usual mode of transmission (introduction, means of spread)

  Despite decades of surveillance and research, surprisingly little is known about the exact mechanisms of M. bovis transmission. Following the classical pathology of cattle cases, current dogma suggests that M. bovis is spread by direct inhalation and exchange of bioaerosols containing bacteria-laden droplets between close contacts. Other MTBC members have different host ranges and have acquired, or retained, capacity to persist in environmental fomites, and they favour a range of different transmission routes. M. tuberculosis is paradigmatic of an airborne infectious disease; most transmission is “direct”, via aerosols in shared and often poorly ventilated airspaces. It would be reasonable to assume that M. bovis shares many of these properties. In cattle M. bovis is believed to be predominantly transmitted between animals by the inhalation of aerosols during close contacts. Some cattle become infected via ingestion; this route may be particularly important in calves that nurse from infected cows (by drinking pooled milk and/or colostrum). Transcutaneous (through breaks in the skin), genital, and congenital infections have been reported but are rare in cattle. Whether, and to what extent, a contaminated environment contributes to persistence and spread remains to be determined empirically but should not be excluded. Although probably context dependent, there is evidence (PCR and metagenomic detections) for some level of environmental survival, which might constitute a short-lived environmental source capable of contributing to indirect intra- and inter-species transmission. Some recent, advanced, multi-host mathematical models explain the observed data better when allowing for some environmental transmission.

  The importance of the routes varies greatly between species. Ingestion appears to be the primary route of transmission for carnivores and scavengers such as pigs, ferrets, and cats, but also probably for non-carnivorous animals, such as deer. In addition, cats might also be infected by the respiratory route or via transcutaneous transmission in bites and scratches. Aerosol transmission also seems to be the main route of spread in badgers, but transmission through bite wounds can be significant, especially in high-density badger populations, as in the South-West of England. Badgers with advanced disease can shed M. bovis in the urine, and organisms have been found in the faeces. Due to behavioural changes, badgers and possums are most likely to transmit M. bovis to cattle during the late stages of disease.

  GAPS :

  Uncertainty over route of transmission between susceptible hosts and how best to mitigate.

  A comprehensive understanding of how/where/when transmission occurs is required to control the disease and to design and deploy effective control measures. Relative importance of potential routes is poorly understood.

• Occasional mode of transmission

  Recent evidence, from GPS-collared cattle and badgers in the UK and Ireland, suggests that direct transmission by infectious droplets or aerosols may not always be the main mechanism for interspecies transmission, raising the possibility of indirect transmission involving a contaminated, shared environment. The possibility that classical pulmonary TB can be simulated and recapitulated in laboratory animal models by ingestion of contaminated feed, is a further intriguing indication of potential environmental risk. It may be that ingestion for some species is able to cause aerosolization that then results in the respiratory system disease pathology that is a hallmark of ‘classical’ mammalian TB. Livestock and wildlife shed M. bovis onto pasture, soil, feedstuffs, water, and other fomites; field and laboratory studies indicate that persistence is possible, but variable, under differing environmental conditions.

  Recent evidence, from GPS-collared cattle and badgers in the UK and Ireland, suggests that direct transmission by infectious droplets or aerosols may not always be the main mechanism for interspecies transmission, raising the possibility of indirect transmission involving a contaminated, shared environment. The possibility that classical pulmonary TB can be simulated and recapitulated in laboratory animal models by ingestion of contaminated feed, is a further intriguing indication of potential environmental risk. It may be that ingestion for some species is able to cause aerosolization that then results in the respiratory system disease pathology that is a hallmark of ‘classical’ mammalian TB. Livestock and wildlife shed M. bovis onto pasture, soil, feedstuffs, water, and other fomites; field and laboratory studies indicate that persistence is possible, but variable, under differing environmental conditions.

  GAPS :

  Relative importance of potential routes is poorly understood.

  Investigation of biophysics of potential aerosolization of bacilli from various fomites may be useful.

• Conditions that favour spread

  Conditions that favour spread would tend to be reflected in the many published context-dependent, classical epidemiological risk factor studies. In cattle, herd size, herd history, restocking/destocking practices, farm fragmentation etc. often feature as risky, although some of these are proxy variables; wildlife exposure variables also feature strongly as risky in such univariable and multivariable models. The outcome of M. bovis infection is variable and will be influenced by environmental (non-genetic) host factors (concurrent infection, nutrition, stress, pregnancy, hierarchy, connectivity, etc.), genetic host factors (genetic immunity), pathogen variation, inflammatory response, and force of infection (dose).

  If a largely airborne infection it would seem reasonable that warm, damp, and poorly ventilated shared indoor airspaces would provide elevated risk of supporting transmission. Host density is likely to be an important explanatory variable and there are risky livestock and/or wildlife management options. Herd husbandry and hierarchy may influence within- and between-herd connectivity. Shared geographic range/sympatry of livestock and wildlife species is a risk especially if wildlife can both become infected and transmit infection to other species. For example, in Britain and Ireland it is recognised that the landscape best suited to grazing cattle, i.e. pasture surrounded by hedgerows and forest, is also prime badger habitat. Interventions to reduce the number of infectious contacts is complicated by sympatry and the role that environmental persistence of bacilli may be playing.

  GAPS :

  Gap in experimental and modelling studies to simulate transmission.

  Host and pathogen genetic and non-genetic factors likely to impact outcome of exposure. Evidence that hosts differ in susceptibility and transmissibility.

  Quantifying the impact (if any) that improving farm biosecurity may have on herd and animal prevalence.

• Detection and Immune response to infection

• Mechanism of host response

  Neither the nature of the protective immune responses that control natural infection, nor the immune processes that cause pathology (immune pathology), are completely understood due to their complex and variable nature, which can be influenced by several intrinsic and extrinsic factors. While Th-1 responses, and in particular interferon-gamma and TNFα, are necessary for both processes, they are not sufficient to account for fully protective immunity or progressive immune pathology. Over recent years several other cytokines have been implicated in protective responses, such as IL-17, IL1β and IL-22, although the relative expression levels of these, and other cytokines/chemokines, is likely to be heavily dependent on several variables e.g. species, breed, stage of infection, comorbidities. These cytokines have also been associated with disease and disease severity and are therefore also linked to pathology. Anti-inflammatory cytokines e.g. Il-10, TGFβ also have an important role in the natural history of infection and the interaction between all these (and other components) has a significant role in disease and diagnostic outcomes. Apart from CD4+ T cells, other T-cell subsets have also been identified as components in the very diverse and multi-faceted immune responses to mammalian TB. These subsets include CD8+ and gamma-delta TCR+ T-cells as well as innate cells such as natural killer (NKT) cells. However, the relative contribution of these T-cell subsets remains to be elucidated. While it is generally accepted that the initial interaction of bacilli with the host is with pulmonary macrophages, the precise relationship of the initial host-pathogen encounter is not fully understood, especially at the sites of infection and disease. Therefore, studies to better define the nature of the host-pathogen interaction, innate and adaptive immunity to infection are essential.

  It is believed that the elimination (clearance) of mycobacteria depends on the microbiocidal activities of the infected macrophages. The ability of macrophages to kill mycobacteria is enhanced after the development of a cell-mediated immune response involving activated T-cells, which produce cytokines, especially interferon-gamma (IFN-γ), which activate microbiocidal properties of macrophages. The role of antibody responses has been quite controversial, and it seems to vary among different species. Even within a single species the consensus on role and relative importance of T-cell and antibody responses is evolving, particularly as methods of detection and characterisation continue to be refined. In addition, the three pathways of the complement system have also been implicated in the pathogenesis of M. tuberculosis and this is likely to be the case with M. bovis. It is now also evident that direct contact between CD4+ T-cells and infected cells facilitates bacillary control within such infected cells. Post-infection, mycobacteria are phagocytosed by local macrophages and/or dendritic cells. Infected dendritic cells migrate to the draining lymph nodes: T-cell activation is initiated at the level of the draining lymph nodes; activated T-cells migrate to the site of infection, attracted by the infected macrophages, activate, and increase the number of mononuclear cells at the site of infection, and contribute to cell death with subsequent development of caseous necrosis.

  GAPS :

  Information on establishment of protective immune response and how a vaccine would be protective is missing. This includes:

  • Correlates of protection: Defining the nature of protective immunity and the immune responses that cause host pathology and to define biomarkers of immunity and disease progression.
  • Defining the role of antibodies in the control of infection and in disease pathology.

• Immunological basis of diagnosis

  Diagnosis might use one of three different components of the host immune response:

  • Delayed-type hypersensitivity skin reaction (DTH): the predominant method for diagnosis of mammalian TB, the skin test, consists of an intradermal injection of PPD (a purified protein derivative from a culture of bovis - bovine PPD) or more specific antigens like ESAT-6 and CFP-10 (research only), which reflect the delayed-type hypersensitivity (DTH) reaction. By using bovine and avian PPD (comparative cervical intradermal test) the specificity of the test is improved.
  • IFN-γ release assays (IGRAs): in vitro stimulation of blood cells with specific antigens (PPD, or more specific antigens, like ESAT-6 and CFP-10, leads to the production of IFN-γ by antigen-specific T cells from infected animals; IFN-γ is detected subsequently by ELISA. IFN-y is undoubtedly an important cytokine in the pathogenesis of bovis, however, other cytokines/chemokines, such as CXCL-10, that can be detected in vitro have also been shown to have some promise as additional tools for this platform of diagnostics.
  • Production of antibodies: although the role of antibodies in the context of a protective immune response is controversial, some animals produce antibodies upon bovis infection. The production of antibodies seems to vary, not just between animal species, but also between animals from the same species. Serological tests to detect antibodies present moderate to high specificity but still low to moderate sensitivity. Several new serological tests have yielded promising preliminary results; however, these tests have not been tested extensively under field conditions in domestic animals and less so in wildlife species.

  Regarding DIVA (differentiating infected from vaccinated): specific M. bovis antigens, such as ESAT-6 and CFP-10, which are deleted in RD1 of BCG, are being evaluated in field trials for diagnosis in cattle alongside BCG vaccination. An alternative DIVA approach, with an engineered or edited BCG and bespoke diagnostic test, is also being evaluated in the UK.

  Bovine and avian tuberculin (PPDs) are crude extracts from specialist mycobacterial culture of reference strains; as such, they are challenging to standardise and there is evidence of manufacturer and batch variation. Progress has been made to create and evaluate a synthetic tuberculin(s) (MDA, molecularly defined antigen) comprised of synthesised peptides and/or recombinant antigens, which should be more amenable to standardisation.

  GAPS :

  Biomarkers in addition or substitution of IFN-γ should be considered to increase sensitivity or specificity of diagnostics. Multiplexing technologies may also be useful in diagnosing and characterising different stages of response to infection.

  Development of a defined set of antigens produced as recombinant antigens or synthetic peptides with which to perform diagnostic tests.

  Validation and field evaluation of novel tests required, including validation of DIVA tests.

  Research on serological diagnostics required. Development of tests for animals other than cattle, including wildlife in developed and developing countries to adapt the existing diagnostics.

• Main means of prevention, detection and control

• Sanitary measures

  Precautionary “clean and disinfect” notices are often provided to herd keepers during mammalian TB outbreaks, although supporting published literature is sparse. Chemical disinfection of slurry, or milk, could be considered, with proper application of “thick lime milk,” likely to inactivate M. bovis within 24 h. However, generation of aerosols in the farm environment may be counterproductive, although no such evidence is published. Sanitation and disinfection may reduce the spread of the agent within the herd. M. bovis is relatively resistant to disinfectants and requires long contact times for inactivation. On infected properties, mechanical, physical, and chemical agents are used to render rooms, materials, fluids, and other substances non-infectious. The most effective methods for destroying mycobacteria are based on the use of heat, such as hot air, burning, cooking, pasteurization, and running or pressurized steam. Ultraviolet light is bacteriocidal at 21-33°C and bacilli are killed within 20 minutes exposure. Effective disinfectants include 5% phenol, iodine solutions with a high concentration of available iodine, glutaraldehyde, and formaldehyde. In environments with low concentrations of organic material, 1% sodium hypochlorite with a long contact time is also effective. M. bovis is also susceptible to moist heat of 121°C (250°F) for a minimum of 15 minutes.

  GAPS :

  Gap in evidence that sanitary measures improve outcomes i.e., resolve outbreaks, reduce recurrence etc.

• Mechanical and biological control

  In countries with established control and eradication programmes, these are based on test-and-slaughter. When test-and-slaughter measures are applied, affected herds are re-tested periodically to eliminate newly infected animals. Infected herds are usually quarantined, and animals that have been in contact with reactors are traced. When test-and-slaughter programme are not possible, or during the early stages of control and eradication programmes, some countries use test-and-segregation programmes, and switch to test-and-slaughter methods in a more advanced and final stage. Enforcement of test and slaughter is difficult in the absence of compensation funds and consequently is very rarely used in developing countries. The use of surplus payments on milk and other animal products can be an alternative to straightforward financial compensation, although it tends to be more effective to higher yielding intensive dairy systems.

  Wildlife intervention options include non-selective culling (proactive or reactive), selective culling (proactive or reactive), vaccination, or some combination i.e., test, vaccinate, remove (TVR). Wildlife (badger) fertility control has been considered; an injectable mammalian contraceptive exists (gonadotropin releasing hormone, GnRH) and mathematical modelling indicates that it might have a role. Antibiotic treatment is not permitted for cattle in the EU and many other territories, on the grounds of food safety and to limit development of AMR. BCG has been shown to reduce susceptibility and pathology in several studies and is currently being considered alongside a DIVA test. Other vaccines are under development; none are currently licensed for livestock or wildlife.

  GAPS :

  Information on efficacy of test and segregation in different contexts could be informative. At least two distinct situations should be considered:

  • separation of the calf just after birth and feeding with treated colostrum.
  • segregation of herds in positive and negative groups and their offspring; maintenance of herds in separate facilities and keeping only the negatives.

• Diagnostic tools

  Diagnostic tools are used in essentially two distinct situations:

  1. to diagnose mammalian TB post-mortem.
  2. to diagnose mammalian TB ante-mortem in live animals.

  A) Mammalian TB diagnosis post-mortem is based in one, or a combination, of the following methods:

  • Detection of mammalian TB-like lesion macroscopically.
  • Histopathology and/or microscopic demonstration of acid-fast bacilli.
  • Isolation of bovis on selective culture media, and confirmation by PCR.
  • PCR to detect bovis directly in clinical samples; WOAH now accepts validated PCR-based direct detection.
  • Molecular epidemiology techniques (e.g. spoligotyping/amplicon PCR/whole-genome sequencing) to distinguish different variants of bovis.

  B) Mammalian TB diagnosis in live animals: assays that index cellular immunity.

  • Intradermal tuberculin test - Single Intradermal Tuberculin (SIT) test using bovine tuberculin and comparative intradermal tuberculin test (SICCT) using bovine and avian tuberculin. The SIT is used widely for mammalian TB diagnosis, although the SICCT provides higher specificity, especially where cross-reactivity from environmental microorganisms is suspected or evidenced. SICCT is used for the initial screening of cattle in some European territories. The USA uses the caudal fold (bovine tuberculin) test for preliminary screening of cattle; reactors are re-tested with the comparative cervical test. SIT is used for preliminary screening of cervids. Intradermal tests are also used for testing non-human primates and lions, African buffaloes, leopards, and African wild dogs in Kruger National Park.
  • IGRAs reported to also detect infected animals that are negative for the tuberculin skin tests. It is used routinely in certain European countries, USA, New Zealand, and other In the EU, IGRAs can be used as an alternative to the skin test for granting and maintaining TB-free status and also movement within the EU in bovine animals. It can also be used for caprine species for movement. When used in combination with skin test (parallel testing) overall sensitivity is increased. It is also useful in animals that are difficult to capture or handle, as they must be captured only once, rather than twice as is the case for the tuberculin tests. An adaptation of this assay has been shown to be useful to test African buffaloes, lion, leopard, and African wild dogs in South Africa.
  • Defined antigens: for use in both skin tests and IGRAs, defined and more specific antigens have been developed based on either synthetic peptides or recombinant proteins. These antigens can also be used to differentiate BCG vaccinated from infected animals (DIVA principle). Example prototype antigens are ESAT-6, CFP-10, Rv3615c and others.

  Mammalian TB diagnosis in live animals: assays that index humoral immunity.

  • Serodiagnosis assays: several tests are currently being evaluated; a few are listed by WOAH. Applicability varies considerably between tests and animal species. Potential advantages might be that they are relatively straightforward, rapid, cheap, and require one visit; they can be deployed remotely or animal-side. The most relevant potential disadvantage remains their lack of relative sensitivity. Protocols which deploy such tests soon after tuberculin administration to boost an anamnestic response are currently being evaluated; dogma, that CMI responses develop earlier/faster than humoral responses in bovisinfected cattle and that an anamnestic boost of antibody responses following tuberculin skin testing enhances serum antibody responses, is being reevaluated.

  GAPS :

  Faster mammalian TB postmortem diagnostics (confirmation tests) needed.

  Better (rapid, sensitive, specific, simple, cost effective) tests for live animals needed for cattle and goat in developing countries and for wildlife worldwide.

  Improved tuberculin testing required, particularly testing synthetic tuberculin.IGRA improvements :

  • Defined antigens need evaluated/validated, also for DIVA use.
  • Large RCTs to consolidate available information on adapting current test for other livestock and wildlife.

• Vaccines

  Injectable BCG remains the lead candidate and best characterised vaccine for livestock and wildlife applications, although oral baited vaccines are being trialled in some settings. BCG is a lab-attenuated variant of wild-type M. bovis, developed in France by repeated subculture and internationally accepted as a TB vaccine in 1927. While not providing complete or sterile immunity, consensus from many studies is that BCG vaccination can reduce susceptibility or substantially reduce M. bovis-induced pathology.

  A recent, relatively small, and context-dependent field trial in Ethiopia estimated “transmission rates” alongside “vaccine efficacy” (i.e., 39% end-point “vaccine efficacy”, as well as estimates for “transmission rate efficacy” of 58% direct, 74% indirect, and 89% total). “Efficacy” was measured for 1 year; “incubation period” is known to be highly variable.

  Recent non-inferiority field trial data from Ireland showed BCG reduced susceptibility in badgers without impacting onward transmission. However, protective efficacy is variable at both population and individual animal levels. BCG will compromise official tuberculin-based skin or blood tests; cattle vaccination with BCG should not be used in countries where control or trade measures are based on such testing; BCG vaccination therefore requires the application of validated DIVA tests, with acceptable performance characteristics.

  BCG is licenced as an injectable vaccine for use in badgers in the UK and early field trials were consistent with a significant reduction in animal-side seropositivity and an indirect protective effect on neonates.

  BCG vaccination is part of the mammalian TB control programme in Ireland, the plan being to phase in replacing reactive badger culling with badger BCG vaccination in a >20,000km² area in Ireland.

  Oral BCG formulation and delivery has been researched for badgers; trace amounts of BCG were detectable in vaccinated badger faeces.

  The mammalian TB vaccine research community communicates and collaborates closely with the human TB vaccine community. New candidate vaccines are currently being screened with heterologous prime-boost vaccines based on BCG vaccination in combination with viral, protein, or DNA subunits, and various adjuvants. Alternative delivery systems are also being considered, such as aerosol delivery, delivery to prime mucosal immunity etc.

  GAPS :

  Larger number of data/results from field studies under natural conditions (field settings) are needed on the topic of BCG vaccination of livestock.

  Validation of DIVA test required for cattle and other livestock for which vaccination is considered, such as goats and SAC.

  Does a prime-boost protocol improve vaccination outcomes?

  Field trials needed to determine efficacy of BCG and/or other vaccine candidates, best route of vaccination (oral, aerosol, injected) in different livestock and wildlife.

• Therapeutics

  Antimicrobial treatment is not permitted for mammalian TB control in livestock in most territories, based on the long duration of treatment, withdrawal times, drug residues in food, and the possibility for continuous ongoing transmission from animals under treatment, and to reduce potential for AMR. The risk of shedding organisms, hazards to humans, and potential for AMR make such treatment extremely controversial. There are very rare reports of human-to-human transmission of AMR M. bovis between immunocompromised cases. Therapeutics have been attempted in some zTB situations but must be performed for long periods and are expensive and accompanied by significant side effects; clinical improvement can occur without bacteriological cure. Limited treatment using human TB drugs has been performed in some valuable wildlife, such as captive elephants, although therapeutic efficacy remains unknown.

• Biosecurity measures effective as a preventive measure

  Risk factors have been investigated systematically in several context-dependent, classical, epidemiological studies. In livestock, herd size, herd history, on farm moves, farm fragmentation etc. often feature as risky, although some of these are proxy variables; wildlife exposure variables also feature strongly as risky in such univariable and multivariable models. Such studies indicate clearly that there may be further options for improved control at farm-level, especially when mammalian TB is viewed as another infectious disease that needs to be controlled. Industry and herd keepers are increasingly familiar with accredited cattle health schemes, which aim to improve control of production diseases, including BVD, IBR, and Johne’s Disease. In such schemes, herd-specific risk assessment data are recorded and analysed, and herd health plans are developed and monitored; biosecurity and biocontainment advice is communicated.

  Risk-based trading could help herd keepers make more informed judgements about purchasing animals and provide an incentive to keep disease free status on farms. However, this may be difficult to implement without outreach informed by social science to ensure stakeholder buy in. In some regions such measures might be viewed as a coercive means of frustrating free trade when they should be viewed as a way of making trade more efficient by addressing the negative externality of disease.

  There will likely be a package of cattle-based “no regrets” measures that should be considered, including risk-based trading, informed purchase, operating a closed herd, regionalisation, genetic selection, risk posed by concurrent infection(s), treatment of waste etc. Herd keepers will likely be advised to take measures to keep livestock and wildlife apart as much as possible, to keep wildlife out of livestock buildings and open feed and feed stores, water troughs, fencing off badger setts on pasture to prevent cattle access etc.

  Specific biosecurity measures may be needed to prevent transmission between livestock and wildlife (and vice versa) in areas where habitats overlap; however, some may be difficult or costly to implement. While such measures have been shown to significantly reduce the opportunities for interaction, published evidence of a directly attributable benefit are lacking.

  GAPS :

  Although apparently common sense, the evidence base around the benefits of biosecurity and farm management measures is lacking.

  Social science research and outreach to stakeholders to reduce fatalism around succumbing to herd breakdowns. Empower farmers to make better trading and biosecurity choices. Mammalian TB needs to be treated like the infectious disease it is, not an occasional occupational frustration.

• Border/trade/movement control sufficient for control

  Effective control and/or eradication on a national scale can only be achieved if there is an improved understanding of the mammalian TB epi-system in such territories. Measures required for disease control are context dependent but will comprise a combination of: improved control over all cattle movements, rigorous pre-movement testing, compulsory identification of cattle, incentives to owners for the slaughter of positive reactors, compulsory testing of cattle within specified intervals as well as the establishment and maintenance of disease-free areas (regionalisation), with the eventual aim of incorporating the whole territory. The success of such campaigns will depend largely upon the political, programmes, and stakeholder commitment, and sustainability within a country, as these affect the availability of funding and resources. Regionalization, accompanied by risk-based cattle trading, has contributed to reduced mammalian TB prevalence in several territories. The existence of seasonal rented grazing and the extent of farm fragmentation in some territories further confounds mammalian TB control.

  GAPS :

  Gap in diagnostic tools adapted to livestock and wildlife for safe transboundary translocation.

• Prevention tools

  Prevention relies mostly on early identification of infected animals, reduction of the contact between infected and non-infected by culling or isolating the infected animals. Measures to prevent contact between wildlife reservoirs and cattle might also be relevant (barriers around hay storage areas, security of feed stores etc). Culling to reduce the population density can decrease transmission. However, each situation must be assessed individually; culling may have unanticipated consequences, such as the transient increase in dispersal of the remaining members of a species, the so-called “perturbation effect”, which has been a feature of larger GB culling trials. Perturbation was not observed in Ireland, potentially as it was transient, as has been suggested in follow up studies in GB.

  Prohibition of supplemental feeding and baiting (feeding of wild ruminants by hunters) may decrease transmission at feeding areas.

  Description of the usefulness of pre-movement tests, to prevent translocation of affected animals, varies depending on reports, based on prevalence, frequency of compulsory test(s), type of skin test in use and interpretation, reagents, and inter-operator variation. Pre-movement testing in cattle is required in some scenarios in some territories.

  GAPS :

  The evidence base around the benefits of biosecurity and farm management measures is lacking.

• Surveillance

  Official passive and active surveillance programme exist in several territories, determined by disease prevalence and trade international rules, and as specified by Competent Authorities, such as WOAH, WHO (zTB), FAO etc. Passive surveillance at abattoir is sufficient in some territories with low prevalence. Active surveillance comprises a structured, regular programmes of animal-level ante-mortem testing using some variant of tuberculin testing, often supplemented by IGRA testing. Should test-positive reactors be disclosed, or suspect lesions be disclosed at abattoir, herds enter a cycle of repeat short-interval testing to remove the burden of infection; strict movement restrictions are often imposed on affected herds until such herds return test-negative results. Various levels of remuneration are paid for slaughtered cases, depending on local programme and legislation. On rare occasions, whole herds are depopulated and bought out. Wildlife surveillance may be either active, in the form of structured and systematic surveys, or passive, but tends not to be as comprehensive as the programme applied to livestock, especially those destined for human consumption. Improved surveillance is required in some territories, to better understand the risks posed by, and to, livestock and other wildlife.

  GAPS :

  Gap in data recording and access in some territories.

• Past experiences on success (and failures) of prevention, control, eradication in regions outside Europe

  As can be inferred from current and historic surveillance and recent phylogeography studies, mammalian TB has been dispersed widely across the globe, apparently facilitated by the relatively recent (within the last 250 years) trade in cattle within and between former colonies, dependencies, and trading partners. There is evidence of subsequent spillover/spillback involving local wildlife in several countries, notably those which have struggled with eradication. Continents and individual countries have experienced different levels of subsequent control and eradication success.

  Despite significant reductions from historically high mammalian TB prevalence (>40% of some national herds) it remains a costly, complicated, and controversial zoonosis in several territories, and a barrier to local, national, and international trade, notably in western Europe. Several other EU Member States experience local mammalian TB micro-epidemics, which have proven challenging to eradicate. Most countries, having mandated tuberculin testing in livestock around the 1950s, experienced dramatic decreasing prevalence. Complete eradication was not achieved in several of these countries, allowing mammalian TB to rebound to troubling extents. The breakthrough in the eradication of mammalian TB was achieved through mandated tuberculin testing, compulsory slaughter of reactors, meat inspection and pasteurisation of milk. Eradication programmes have been effective in several European countries, USA, Australia, Cuba, and other countries. Relative control of mammalian TB in the USA is rightly hailed as one of the great successes of veterinary science, although there remain troublesome risks in some areas, including the Michigan epi-system, the Texas-Mexico border etc. Comprehensive and sustained programmes of herd testing, regionalisation, risk-based trading, and active removal of the risk from wildlife reservoirs allowed Australia to achieve Official TB-free Status. New Zealand is well on the way towards eradication, facilitated by a highly collaborative effort involving industry and government. However, sporadic outbreaks, some of which are still associated with local wildlife (possums) are confounding the final stages of eradication.

  GAPS :

  Meta-analyses of national programme performance, including risk factor analyses, would be useful.

• Costs of above measures

  Very expensive, if not prohibitive in some territories. From October 2022 to September 2023, 19,506 cattle were slaughtered due to a mammalian TB incident in England, the fewest since 2007; a similar number of badgers were also removed in that period. For example, mammalian TB eradication costs UK taxpayers ~£150 million per annum, with additional costs falling to the cattle industry. In Ireland, annual mammalian TB control costs increased from €82 million in 2015 to €97 million in 2020.

  GAPS :

  Economics research to update the herd-, territory-, and country-level full economic (monetary and non-monetary) costs of mammalian TB to stakeholders, taxpayers, competent authorities etc. Update and model potential impacts on local, national, and international trade.

• Disease information from the WOAH

• Disease notifiable to the WOAH

  Yes.

• WOAH disease card available

  Bovine tuberculosis

• WOAH Terrestrial Animal Health Code

  Infection with Mycobacterium tuberculosis complex.

• WOAH Terrestrial Manual

  Mammalian tuberculosis (Infection with Mycobacterium tuberculosis complex).

• Socio-economic impact

• Zoonosis: impact on affected individuals and/or aggregated DALY figures

  Estimates of the global burden of zoonotic tuberculosis (zTB) in humans are caveated and imprecise but currently appear to constitute ~1.4% of the human burden, predominantly in LMIC. WHO estimated 147,000 new cases of zTB in humans and 12,500 deaths in 2016. Data on DALY are sparse and not well compartmentalised. A 2019 global estimate cites human TB DALYs (count) as 65.1M, and age-standardised rate per 100,000 human population at 840·8 for all ages (zTB compartment not resolved in this analysis).

  GAPS :

  Impact of mammalian TB and zTB on DALYs largely unknown, especially for developing countries. Strengthen surveillance of zTB.

• Zoonosis: cost of treatment and control of the disease in humans

  The direct cost of TB treatment varies widely depending on the country-specific health care and drug susceptibility of the pathogen. For example, the average expenditure for the diagnosis and treatment of TB in low- and middle-income countries ranges from US$ 55 to US$ 8,198 per patient. As M. bovis is resistant to pyrazinamide, standard treatment regimens (usually 6 months) are extended to 9 months, adding to cost.

  GAPS :

  Short(er) course treatments would be an improvement.

• Direct impact (a) on production

  Mammalian TB outbreaks are extremely disruptive and often devastating, presenting serious challenges to the management and sustainability of farm businesses i.e., losses at slaughter, milk disposal, culling at youngest ages, replacement losses due to the need to buy additional cattle, costs incurred with unplanned additional feeding, etc. Generalised infected carcasses are often rejected for sale and consumption.

  A few economic studies have estimated the full economic (direct and indirect) costs of mammalian TB outbreaks, both to herd keepers, industry, and taxpayers; such studies inform cost- and responsibility sharing. In the UK, there were large context-dependent variations in consequential costs, with dairy herds experiencing higher costs than beef herds, although costs per head were higher in beef herds. Testing costs, output losses, and movement restrictions dominated.

  More recently, the impact on human mental health has been considered significant and will have an underappreciated effect on the farm business.

  GAPS :

  Some economic estimates of impact of mammalian TB on stakeholders. Sparse information exists on the direct impact on production in countries where the disease is not under control.

• Direct impact (b) cost of private and public control measures

  Control measures in many countries based on variations of test-and-cull policies. Programme costs (contracted official testing, valuation, and compensation) are very high and escalate with increasing prevalence. Direct and indirect costs incurred by herd-keepers, including loss of production genetics built over generations.

  GAPS :

  Some economic estimates of impact of mammalian TB on stakeholders. Sparse information exists on the direct impact on production in countries where the disease is not under control.

• Indirect impact

  Mammalian TB outbreaks are extremely disruptive and present serious operational, financial, and emotional challenges to the management and sustainability of farm businesses. Impact strongly context-dependent and depends on the level of mammalian TB prevalence/incidence and how that is viewed by trading partners. The possible loss of genetic value (when it affects selected animals of breeding programme or protected autochthonous breeds) might be of relevance. Mammalian TB outbreaks in rare native bovine breeds, or for example rare bison in USA, may be of concern from a biodiversity perspective. Also hunting industry impact for wildlife TB.

  GAPS :

  Some economic estimates of impact of mammalian TB on stakeholders. Sparse information exists on the direct impact on production in countries where the disease is not under control. Unknown impact on tourism (hunting, game sales, ecotourism) as well conservation for wildlife TB.

• Trade implications

• Impact on international trade/exports from the EU

  There is an evidenced risk of inadvertently exporting infected cattle to Officially Tuberculosis-Free status (OTF) regions from a region with mammalian TB. Pre- and post-movement testing may not resolve this problem due to limited test sensitivity. The same argument applies to other traded species, such as SACs, goats etc.

  GAPS :

  Should be possible to model the impact of such trade.

• Impact on EU intra-community trade

  Mammalian TB is a barrier to trade, particularly in live animals. Controls on movements include pre-movement testing where appropriate and may have impact on the intra-community trade; for more information see –Bovine tuberculosis - European Commission (europa.eu)

  GAPS :

  Economic and epidemiological modelling studies.

• Impact on national trade

  Mammalian TB is a barrier to trade, particularly in live animals. Movement controls and appropriate restrictions exist within countries with mammalian TB control strategies to prevent movement of infected animals from one region to another. In some territories, mammalian TB confirmed herds are prohibited from selling livestock or from bringing susceptible livestock onto their premises; they can only move cattle direct to slaughter. This could include game species such as cervids, or African buffalo.

  GAPS :

  Economic and epidemiological modelling studies.

• Links to climate

  Seasonal cycle linked to climate

  In some territories there is an apparent seasonality in detections of mammalian TB, which may reflect that cattle tend to be housed over winter and more amenable to testing, illustrating how weather and climate impact farming activities and behaviours. Seasonality in cattle movement and trade may be relevant to disease control. Whether seasonality in relative susceptibility exists (i.e., pregnancy, vitamin D deficiency, and sunlight), should be investigated. Research has investigated the role of ambient temperature on disease diagnostics, e.g., IGRAs. Regarding potential environmental survival, ultraviolet radiation has been hypothesised to reduce survival time, while cooler temperatures seem to be associated with persistence. Regional variation in weather effects can be considerable and could lead to heterogeneous outcomes. If environmental persistence and indirect transmission are shown to be major players in disease dynamics, climate change may modulate future disease risk.

  GAPS :

  Gap in knowledge about how climate affects farming behaviour and exposures.

  If indirect transmission from the environment is a significant source of exposure, developing a better understanding of how climatological factors may influence environmental survival would be useful alongside predictions on how changing climate might affect trends.

• Distribution of disease or vector linked to climate

  Infected livestock, wildlife, companion animals, and humans could be classified as mammalian TB vectors in the sense that they represent living agents that carry and transmit pathogens to other susceptible living agents. The impact of concurrent infections on susceptibility, pathogenesis, and diagnosis should be considered. For example, there is evidence that helminths impact mammalian TB pathogenesis and may confound diagnosis of disease states. Western Europe is predicted to become milder and wetter and even more permissive for helminths.

  The role of climate variables in mammalian TB distribution is underreported and probably underappreciated. Temperature- and moisture-related climatic indicators, especially their timing and variability, appear to be more important predictors of mammalian TB in England and Wales than do variables related to vegetation or land-use. The transmission of mammalian TB may be linked to the seasonality and sequence of ecological events during the year and is probably sensitive to changes in this seasonality from one year to the next. This aspect of epizootiology is rarely incorporated into statistical models of disease distribution and points to the type of process-based biological model that will be most appropriate for mammalian TB.

  Evidence from Spain suggests that when animals are extensively managed in an extremely dry season, with limited water resources, an increase in animal contacts might facilitate mammalian TB transmission.

  GAPS :

  Influence of seasonal variations, climate change, global warming and consequent movement of animals is unknown on the prevalence and distribution of the disease. Consider integrating such data in mathematical models.

• Outbreaks linked to extreme weather

  Unaware of such reports but should be kept under review.

• Sensitivity of disease or vectors to the effects of global climate change (climate/environment/land use)

  The impact of adverse weather on food availability for livestock and wildlife may conceivably result in alterations of mammalian TB transmission dynamics, that might occur in opposite directions: a) a reduction in the population density of the reservoir hosts with a consequential reduction in disease transmission between cattle; b) a reduction in the immune response and/or increased susceptibility might increase M. bovis transmission. The normal cycle of seasons and weather will probably influence the opportunities for disease maintenance and spread in the various hosts of M. bovis, as well as the opportunities for intra- and inter-species transmission at that interface. For example, whether there is enhanced or reduced opportunity for wildlife and livestock to interact in adverse weather would need to be investigated systematically. Wildlife may adopt hibernation, or torpor, or may seek out food or shelter with livestock to tolerate adverse weather; disease dynamics would be different.

  The potential interaction between animal infectious diseases, including mammalian TB, emissions, and climate change have been considered: https://ruminanthw.org.uk/wp-content/uploads/2022/04/SO-634-Ruminant-Report-Methane-April-2022-web.pdf

  GAPS :

  Influence of seasonal variations, climate change, global warming and consequent movement of animals is unknown on the prevalence and distribution of the disease.

• Main perceived obstacles for effective prevention and control

  • bovis has multiple susceptible mammalian hosts.
  • Mammalian TB is challenging to diagnose antemortem and postmortem; unusually antemortem diagnosis tends to rely on cell-mediated immunity and there is effectively no gold standard.
  • Official diagnostics have suboptimal performance characteristics, especially test sensitivity and convenience.
  • Control of mammalian TB in some countries is confounded by the existence of well documented wildlife reservoir(s).
  • Progress is being made on cattle vaccination trials and the development and evaluation of DIVA tests.
  • Regulatory (safety and efficacy) requirements for potential introduction of cattle vaccination plus DIVA testing; trading partners will have their own requirements.
  • Lack of economic conditions to establish test-and-slaughter control programmes in most developing countries as control measures result in significant economic losses.
  • Roles, responsibilities, and cost sharing can be an adversarial blame game between stakeholders, who should be working towards the same goal.
  • Different models of cost and responsibility sharing between competent authorities and industry stakeholders in different territories.

  GAPS :

  • Uncertainty over route of transmission between susceptible hosts and how best to mitigate.
  • Lack of rapid, cost-effective, animal-side(?) test(s) with well documented performance characteristics.
  • Increased KT and behaviour/social science required; evidence of (dis)confirmation bias and misinformation/misunderstanding across the spectrum of stakeholder views.
  • Potential to develop synthetic tuberculin, either modified peptides or recombinant antigens, which are easier to manufacture, QC, and standardise.
  • Objective, independent, RCTs of novel mammalian TB diagnostics and vaccines.
  • Few studies on intervention and management evaluations.

• Main perceived facilitators for effective prevention and control

  • Political and stakeholder commitment, KT, and social/behavioural science.
  • Effective KT, trusted advisors and partnership working, especially evidenced to counter (dis)confirmation bias and misinformation.
  • Availability of resources (human and economical).
  • Commitment of all sectors involved in the programme, including policymakers/government, veterinarians applying the diagnostic tools and abattoir surveillance, and, most importantly, herd keepers.
  • Increased transparency and availability of disease data.
  • Trained public health personnel and public education help on the implementation of mammalian TB control programmes taking into consideration existing cultural and societal constraints.
  • Rigorous (quality controlled) and rational implementation of existing tests should be reinforced.

  GAPS :

  • Lack of social/behavioural science to inform on extent of existing knowledge and barriers to acceptance of advice.
  • Lack of economic modelling, option appraisals, and full economic costs of various potential interventions.

Global challenges

• Antimicrobial resistance (AMR)

• Mechanism of action

  N.A.

• Conditions that reduce need for antimicrobials

  N.A.

• Alternatives to antimicrobials

  N.A.

• Impact of AMR on disease control

  N.A.

• Established links with AMR in humans

  Rare reports of AMR M. bovis affecting humans (mostly immunocompromised).

  GAPS :

  M. bovis isolates would tend not to be screened for AMR.

• Digital health

• Precision technologies available/needed

  Only in small number of research facilities.

  GAPS :

  Improved wildlife ecology and surveillance.

• Data requirements

  Livestock ID, test history, movement records, pedigree. Wildlife surveillance. Requires complex and costly relational databasing.

  GAPS :

  Widen availability of data on all epidemiologically relevant susceptible hosts. Surveillance of wildlife hosts – abundance and species distribution models.

• Data availability

  Livestock data exceptionally well recorded in a small number of countries.

  GAPS :

  Widen availability of data.

• Data standardisation

  QC certification and accreditations exist.

  GAPS :

  Widen availability of data.

• Climate change

• Role of disease control for climate adaptation

  Improved animal health should contribute to reduced emissions through efficiency gains and reduced need to replace mature animals.

  GAPS :

  Mathematical modelling.

• Effect of disease (control) on resource use

  Improved efficiency and sustainability.

  GAPS :

  Systems modelling.

• Effect of disease (control) on emissions and pollution (greenhouse gases, phosphate, nitrate, …)

  Improved animal health should contribute to reduced emissions.

  GAPS :

  Update mammalian TB-specific and concurrent infection abatement models.

• Preparedness

• Syndromic surveillance

  N.A.

• Diagnostic platforms

  Official testing largely harmonised. Variations on themes in Reference Labs. Limited animal TB reference labs in developing countries.

  GAPS :

  Modernisation desirable to PCR, WGS etc.Objective evaluation of novel diagnostics required.Reference biobanks.

• Mathematical modelling

  Various models published. i.e., agent-based, compartmental, multi-host etc.

  GAPS :

  Crucial to model control and interventions.Crucial to model control and interventions.

• Intervention platforms

  Likely to require a package of livestock- and wildlife-associated control measures.

  GAPS :

  KT and social/behavioural science important. Informed behaviour changes in all actors.

• Communication strategies

  Can be polarised and pre-judged subject. Often seen as Government and governance problem.

  GAPS :

  KT important. Collaborative cost- and responsibility-sharing communications required. Advisory service important role. Informed behaviour changes in all actors. Social science engagement and outreach may help to improve stakeholder buy in / compliance.

Main critical gaps

• • Lack of rapid, cost-effective, convenient, test(s) with desired performance characteristics e., test sensitivity, specificity, NPV, PPV etc.; measures dependent on true prevalence of mammalian TB in the area/population where tests are applied, and not a direct characteristic of the test per se. Consequently, apparent prevalence will significantly underestimate true prevalence in whichever host is being surveyed, with the result that the epidemic is largely unobserved and there are hidden burdens in various hosts.
  • A comprehensive understanding of how/where/when transmission occurs is required to control the disease and to design and deploy effective control measures. Relative importance of potential routes is poorly understood.
  • Social/behaviour science in relation to knowledge exchange and acting on advice.
  • Limited understanding of the role of livestock movement (recorded and unrecorded moves), rented seasonal grazing, and farm fragmentation in some territories.
  • Mathematical modelling of epidemic and control options in the absence of prohibitively expensive RCTs.
  • Immunological correlates of protection are not sufficiently understood to inform vaccination strategies.
  • The full spectrum and consequences of mammalian TB exposure, immune responses, and disease are not fully understood, neither are many epidemiological or pathological metrics.
  • Susceptibility will be impacted by genetic and non-genetic factors, including force of infection; how these factors interact has not been fully investigated.
  • The impact of concurrent infection(s) on mammalian TB diagnostics, vaccination, and genetic selection are under researched.
  • While encouraging progress is being made in evaluating BCG vaccination in cattle and in the development of an accompanying DIVA test, results of sufficiently controlled, powered, and replicated field trials or RCTs are awaited. There may be future regulatory or trade issues.
  • The evidence base around the benefits of biosecurity and farm management measures is lacking.
  • With notable exceptions, the impact of wildlife vaccination on mammalian TB in cattle is lacking currently.
  • Relationship between diagnostic status and infectiousness is not known with any precision.
  • Lack of a “gold standard” and independent evaluation for mammalian TB antemortem and postmortem diagnostics; specialist culture would be considered the “reference” standard.

Conclusion

• • A better understanding of transmission pathways and risk factors for mammalian TB transmission is required and there is also a need to improve diagnostics and vaccine options.
  • There are knowledge gaps around the role of the environment in mammalian TB transmission and in many countries the role of wildlife, implicated in the transmission of mammalian TB, is not known. Further studies are needed to better understand transmission dynamics between probable wildlife maintenance hosts and cattle.
  • The role of environmental persistence of bovis needs further investigation to assess its role in the epidemiology and transmission of mammalian TB to cattle. Genetic resistance, the possibility, and implications, of latency of M. bovis in cattle and the host-pathogen relation in cattle and wildlife species are areas that could be targeted by researchers.
  • The role of tuberculosis infection in cattle as a reverse zoonosis, especially in developing countries should be further investigated.
  • To allow a better identification of areas at risk, the World Animal Health Information Database has been created, providing access to all data held within the WOAH’s new “World Animal Health Information System”. Not all countries are represented, and the quality of data is variable and could be improved. Data are available for domestic animals, but also for wildlife; a yearly report is available.
  • Although context dependent, control measures need to be applied, not only to livestock, but also to wildlife in areas where mammalian TB incidence is high, and wildlife are implicated. Trade measures, recommended by the WOAH, should be applied.

Sources of information

• Expert group composition

  2016 Expert group members included with permission:

  Glyn Hewinson, AHVLA, UK - [Leader]; Martin Vordermeier, AHVLA, UK; Kevin Kenny, Research Officer, DAFM CVRL, Ireland; Tiny Hlokwe, ARC-Onderstepoort Veterinary Institute, South-Africa

  2024 Expert group members included with permission:

  Robin Skuce, AFBI, Northern Ireland, UK, [Leader]

  Adrian Allen, AFBI, Northern Ireland, UK, [Co-leader]

  Tom Ford, AFBI, Northern Ireland, UK, [Co-leader]

  Beatriz Romero Martinez, VISAVET, UC Madrid, Spain

  Daniel O’Brien, Michigan State University, USA

  Eamonn Gormley, UCD, Dublin, Ireland

  James McCormack, APHA, UK

  Jason Sawyer, APHA, UK

  Javier Bezos Garrido, VISAVET, UC Madrid, Spain

  Maria O’Hagan, DAERA, Northern Ireland, UK

  Michele Miller, Stellenbosch University, South Africa

  Mike Coffey, Scotland’s Rural College, Edinburgh, UK

  Stephen Gordon, UCD, Dublin, Ireland

  Francisco Olea-Popelka, Western University, Ontario, Canada.

  Please cite this chapter as: Skuce R., Allen A., Ford T., Romero Martinez B., O’Brien D., Gormley E., McCormack J., Sawyer J., Bezos Garrido J., O’Hagan M., Miller M., Coffey M., Gordon S., Olea Popelka, F., 2024. DISCONTOOLS chapter on bovine tuberculosis.https://www.discontools.eu/database/74-bovine-tuberculosis.html.

• Date of submission by expert group

  September 2024

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