Control Tools

• Diagnostics availability

• Commercial diagnostic kits available worldwide

  Most often detection and identification relies on traditional bacteriological culture for which procedures are usually in-house validated in diagnostic or research laboratories.

  The availability of diagnostic kits at national disease laboratories is variable, and sensitivities and specificities of the used tests are highly variable between tests and serotypes. For some of the kits, no validation has been carried out or at least published.

  List of commercially available kits (Diagnostics for Animals)

  GAPS :

  There are different diagnostic tests with respect to strengths and weaknesses and no recommendations on how best to test in which scenarios exist.

  There is a lack of recommendations on how the various available tests with their strengths and weaknesses can be used in different scenarios with regard to APP. However, this would also require national epidemiological analyses for APP in order to derive such recommendations for the different infection scenarios.

  There is a need for harmonization or comparative analyses of available commercial diagnostic kits. Each test is only fit for a specific purpose.

  There is a need for kits fulfilling EU requirements to be used in diagnostics.

  There is a need for centralized (EU) registration procedures in case registration of diagnostic kits becomes compulsory (as proposed by WOAH).

  There is a need to avoid high extra costs when a kit is intended to be introduced in a non-EU country. The expenses derived from taxes and importation, along with the time required, which makes it nearly impossible (i.e. Latin America) to implement the test. It would certainly be helpful if diagnostic tests for APP were easily and affordably available worldwide.

  Diagnostic kits for detection and subtyping should accomodate the new serotypes detected in the last years, especially serotypes 18, 19 and all serotypes which will be detected in the future.

  Commercial diagnostic kits to measure antibodies against different Apx toxins would be useful.

• Diagnostic kits validated by International, European or National Standards

  Unknown.

  GAPS:

  There are no national or international standards for diagnostic kits. There is a need to develop a gold standard and a single procedure for centralized registration, based on a comprehensive dossier.

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

  Unknown.

  GAPS:

  There is need for guidelines on this particular topic, including modern molecular techniques.

  Guidelines to diagnose disease and causation are available or to be derived from handbooks. Guidelines to assess the infection status of herds are neither broadly available nor well accepted.

  Well accepted guidelines are especially needed for substantiating absence of infection and for certification of herds as SPF for APP infection with high certainty.

• Commercial potential for diagnostic kits in Europe

  Tremendous priority has the development of standardized specific and sensitive diagnostic procedures including sampling method, sample size and test for herd examinations. An accurate bedside test based on nasal mucus, tonsils, saliva or blood for antigen/antibody diagnostic would facilitate disease management and disease identification which subsequently enables the prudent selection and use of antimicrobials (or not). Especially the identification, if bacterial agents are involved in disease pathogenesis and not only viruses would contribute to treating only animals that suffer from bacterial disease.

  Pen-side tests with commercial potential have been described in the literature based on, e.g., CRISPR-Cas or LAMP but have yet to be commercialised. As per the point above – it would be better if the test for APP was part of one that also detected relevant bacteria and viruses of the PRDC.

  GAPS :

  Tremendous possibility for any accurate test to correctly identify APP and also to assess the virulence potential of the respective strain reliably.In addition to serotyping, further diagnostic tools in the future might be valuable, because there is a clear relationship between some pathogenic serotypes (9/11, 5, 1) and high virulence, but also atypical isolates occur.Serotyping of starins in combination with serotype-specific detection of antibodies is useful to follow infection dynamics in a herd by serology.

  Diagnostic procedures for strain characterization, amongst others serotyping, WGS and others, for epidemiological or ‘forensic’ investigations, are not yet widely commercially available.

  A pen-side APP test that is part of one that can distinguish the viral and bacterial pathogens of the PRDC should be developed. Selling point is reduction in antibiotic use.

  Sequencing (e.g. nanopore sequencing) has major potential to optimize diagnostics, as often, respiratory problems are multimicrobial. In addition, typing of the APP strains can be obtained by sequence analysis. Further research is needed, and also the cost of analysis should be reduced.

  There is a serious need for a commercial kit detecting antibodies against ApxI, II and III to be used with toxin-based vaccines. Up to date, there is no way to measure levels of maternal antibodies against these toxins that may interfere with piglet vaccination.

• DIVA tests required and/or available

  Unlikely to be of much use, a DIVA test covering all serotypes would be a tool to test animals, if they are completely free of all APP serotypes, although animals might have been vaccinated and therefore have vaccine-induced antibodies against APP. A certification, that these animals are free of APP would be possible. A DIVA test may eventually have a place if vaccination is part of a strategic plan to eradicate.

  One or two DIVA tests have been developed experimentally using a modified APP serotype 2.

  Apx IV, which is only produced in vivo after infection, can be used in combination with vaccines (not having this toxin) in its formulation as a marker for positive carrier animals in vaccinated animals. A limitation of the Apx IV ELISA diagnostic kit is the sensitivity of this test, which could be low and serotype dependent.

  Serotyping based on capsular genes by PCR test is widely used in veterinary diagnostic labs and there is a clear route to identifying possible new serovars via genome sequencing as a last resort (Stringer et al. (2021).

  GAPS :

  DIVA tests are required but not available.For the economic control it would be helpful to distinguish between vaccinated and infected pigs to monitor interventions.

  It could be an important matter for companies dealing with genetics in international trades (from EU to other countries) to have a DIVA test available.

  The specificity of the ApxIV-ELISA tests is actually quite high (100% specific tests do not exist), while sensitivity can be too low. Problematic is the lack of a convention to the method of acting upon detection of (false) positive test results for unexpected situations (e.g. APP free herds).Also occasional strains where an insertion of a genetic element, e.g., ISApl1, into the apxIV gene prevents it being expressed. The quality of the ApxIV test concerning its sensitivity and specificity should be determined under different conditions and in different stages of infection.

  For live attenuated vaccine use – alternatives to apxIV as a DIVA antigen might be useful.

• Vaccines availability

• Commercial vaccines availability (globally)

  A wide variety of vaccines are available worldwide. Commercial bacterins or toxin-based vaccines are available, but not in all countries. Mostly not purified toxins but growth supernatants are used. In addition, autogenous vaccines are nowadays marketed by different producers, and in some cases produced by veterinarians themselves. There are almost no commercial vaccines used in North America presently, where almost all of them are autogenous vaccines.

  Mixed vaccines (bacterins and toxin-based) became available last years.

  A wide variety of experimental vaccines have been tested.

  GAPS :

  There is a need for more efficient commercially available vaccines. They should be either more broadly effective, regarding the number of serotypes that they provide clinical protection to, and efficient in reducing transmission of APP in vaccinated animals.

  There is a need to do research focused on the reduction of injections (new application routes), e.g. mucosal or intradermal vaccination, or to result in fewer carriers.

  Mixed vaccines (bacterins and toxin-based) became available last years. No commercial test to routinely measure antibodies against the toxins in vaccines is available. The standardization of a test-antibody detection-combination will allow making robust comparisons between vaccines.

  There is a need to speed up/ facilitate the registration procedures, particularly for GMOs.

  There is a need of standardisation for autogenous vaccines (adjuvants among other factors). Some laboratories recommend a single vaccination in piglets but there is no scientific validation of this recommendation.

• Marker vaccines available worldwide

  Not known.

  Vaccines do not contain ApxIV, which is only produced after infection in vivo. Therefore the Apx IV ELISA can be used to detect infection also in vaccinated animals.

  GAPS :

  Apx IV can be used in combination with the use of a subunit vaccine (not having this toxin) or with bacterins in its formulation as a marker.

  Marker vaccines based on knock-out mutant strains have been used experimentally and should be further investigated.

• Effectiveness of vaccines / Main shortcomings of current vaccines

  Most of the vaccines do not cover all serotypes. A vaccine containing toxoids is believed to give reasonable protection against most strains.The problem for autogenous vaccine production is that the right strain must be isolated for the vaccine. Selection of adequate diseased pigs for strain isolation from altered lung tissue is the basis for further production of autologous vaccines.If diagnostics are wisely used (i.e. right animal(s), timing and samples), the relevant APP can be isolated easily and affordably from diseased and sacrificed animals.In most cases clinical disease is induced by a single serotype. If there are pigs from many different sources mixed in the farm, performing multiple bacterial isolations and (sero-) typing will reveal if there are more than one strain involved. This procedure can be particularly difficult when a herd may have several types causing a problem in the same herd. The point about multiple serotypes in a herd or a single animal is critical. Currently, diagnostic labs usually only take one morphological representative colony for further identification, thereby missing multiple serotypes and may explain some of the autogenous vaccine failures. Alternatively, routinely some do serotyping directly on lung samples as well, which can pick up different serotypes in a single animal.

  The one strain is needed, which causes the disease, but not the one masking the problem. The right diagnostic strategy is therefore crucial in order to detect the relevant APP types. Subunit vaccines have the benefit of covering all serotypes possessing or producing the units present in the vaccine.

  The summary of the commercial vaccine product characteristics clearly claim the potential protectivity achievements, which can be reached by the respective vaccine.

  Internal biosecurity measures as e.g. avoidance of mixing pigs after weaning instead of litter-wise introduction to nursery pens and prevention of other trigger factors (e.g. air draught) can support vaccine efficacy.

  GAPS :

  A problem of vaccines and vaccine efficacy is the use of vaccines as therapeutic vaccines and less intended to control transmission and achieve freedom of pathogen as known for notifiable disease vaccines.

  The reason, why the minimum acceptable efficacy levels for a vaccine as decreasing mortality, reducing economic losses, having no side effects, etc. might not be reached on a farm, should be addressed by vaccine producers next to the available summary of product characteristics, which clearly claims the protectivity level of the vaccine.

  Toxin-based vaccines might not have been tested with all serotypes. Some serotypes produce only one toxin and protection by only neutralising a simple toxin might not be sufficient. There is a need of validation of such vaccines for protection against more serotypes including those described in the last years.

  It is expected, that a “suicide” live attenuated vaccine that is able to produce toxins in a controlled manner (with subclinical outcome) will be able to develop cross-protection across serotypes.

  Development of vaccines that cover “groups” of serotypes (polyvalent vaccines) sharing antigenic determinants will facilitate protection.

  There is a need for more effective vaccines that do not interfere or are impaired by maternal antibodies present at very young age. Weaned pigs (between 4-12 wks) often have high levels of maternal antibodies which may interfere with needed vaccination.

  Also duration of efficacy of vaccines should be longer. Now it is ~16 weeks, but vaccines that work ~24 weeks or longer would be desirable. In that way one can vaccinate weaners and have efficacy up to slaughter.

  Also most vaccines need a booster after 2-4 wks. Preferably vaccines are developed that need only one shot.

• Commercial potential for vaccines in Europe

  Current commercial vaccines provide very variable results. Protection is not just depending on particular serotype but also depending on particular strain present on herd.

  Not always good protection against clinical disease by current APP vaccines provided, although APP strains responsible for disease are covered by the vaccine.

  GAPS :

  Need for market research in terms of antibiotic replacement/limitation/prohibition, and if the increase of vaccination can be a direct consequence. Due to the fact that vaccines sometimes are not working well, a risk analysis for vaccine failure should be elaborated.

  Need for more efficacious vaccines. In some particular situation use of commercial vaccines make no improvement at all on clinical presentation.

• Regulatory and/or policy challenges to approval

  None.

  GAPS:

  For marker vaccines or modified vaccines considered to be GMO the approval procedure in the European countries in contrast to North America is hard and time consuming. These distortions of competition should be avoided

  In case of live vaccines, the use of antibiotics as promoters or therapeutics is a concern for vaccine producers.

  EMA: Effects, side-effects and compatibility should be elaborated on.

• Commercial feasibility (e.g manufacturing)

  Unknown.

  GAPS:

  In the case of live vaccines, a balance between vaccine efficacy and market expectations should be established.

• Opportunity for barrier protection

  Probably unlikely.

• Pharmaceutical availability

• Current therapy (curative and preventive)

  Therapy relies on antibiotics and sensitivity testing following bacterial culture. Using CLSI clinical breakpoints (CBPs) concordance between antimicrobial resistancy (AMR) genotype and in-vitro antimicrobial susceptibility pattern (phenotype) was shown for florfenicol and enrofloxacin, but cannot be evaluated for some other antimicrobial substances (e.g. trimethoprim-sulfamethoxazole), because no CBP are available.

  Usually the resistance phenotype is vertically transmissed in a population, so that consideration of the epidemiological link between age is a good criterion to optimise the antimicrobial use (Vilaró et al. 2024). Continual monitoring of MICs is required to suggest the best choices to practitioners. The debate on antibiotic usage will shift attention from treatment with antibiotics to preventive measures.

  Less options for treatment are available as local registration of products expires. Pharmaceutical companies seem not interested in renewing registration as sales dropped.

  GAPS :

  There is a need to study the impact of antibiotic treatment in the overall profitability of the industry, and to compare it with vaccination as an alternative.

  More options for treatment must be ensured although the business opportunity for renewing registrations in a decreasing market for pharmaceutical companies is unfavourable.

• Future therapy

  Therapeutic intervention of diseased pigs with antimicrobial substances is mostly successful and antibiotic resistancy patterns are mostly not a cause of concern (Hennig-Pauka et al. 2022). APP as the cause of inflammation should be eliminated, but therapeutic interference in the inflammatory process may support recovery. It is the host response, principally the death of macrophages and neutrophils, that causes the damage due to enzyme release.

  GAPS :

  Improved knowledge of genetically defined host susceptibility will offer new therapeutic intervention strategies.

  Any pathogen-selective therapy is beneficial for overall animal health. New effective antimicrobials drugs with short withdrawal period should be developed

  Efficient alternative medication approaches, other than chemical antimicrobials, are needed.

  Dispersal of biofilms is needed to limit the reservoir for App.

  Further development should be made in knowledge on preventive therapy or preventive feed ingredients against carriers or to reduce shedding / bacterial load, which would reduce transmission and thereby reduce the probability of disease.

  Antibiotic treatment as a tool to eliminate carriers should be deeper investigated in order to elaborate elimination programmes.

• Commercial potential for pharmaceuticals in Europe

  Probably good potential with anti-inflammatories and antibiotics, but this depends on the scope of the future limitations in the use of antibiotics in farm animals in different parts of the world.

  GAPS :

  Antimicrobial substances not used in human medicine should be developed for treatment.

• Regulatory and/or policy challenges to approval

  None that can readily be identified.

  There is inequality in the EU on the interpretation and approval of use and manufacturing of autogenous vaccines or the origin of the bacteria to be used for autogenous vaccine production. This may result in unfair competition and transport of diagnostic material / autogenous vaccines across borders with different interpretation of regulation(s).

  There is also inequality on the interpretation of the EU regulation to be allowed to devoid from commercially available vaccines and choose autogenous vaccines. This unclarity may result in some cases that commercial producers do not opt for further development of commercial vaccines as autogenous vaccines are cheaper and thus the business case of new vaccines are not certain.

  GAPS :

  All pharmaceuticals should be assessed according to their withdrawal times to avoid residues and to ensure safe and wholesome pork. In general treatments should be shortened and efficacy should be ensured.

• Commercial feasibility (e.g manufacturing)

  Unknown.

  GAPS:

  New molecules should be available at a reasonable price.

• New developments for diagnostic tests

• Requirements for diagnostics development

  Further studies of the bacterial genome and virulence factors are required.

  GAPS :

  A higher sensitivity of antibody tests only detecting antibodies after infection not vaccination (e.g. ApxIV-ELISA) should be achieved.

  Cheaper methods (e.g. LAMP loop-mediated isothermal amplification) or pen-side tests should be developed to sample larger numbers of living pigs (tonsillar sampling) to detect carrier status in specific age groups and reveal infection dynamics on farms.

  Reliable detection and simultaneous typing (serotype, virulence, resistance) using new sequencing methods must become even better and cheaper.

• Time to develop new or improved diagnostics

  Time to develop new systems is increased with the time required to solve regulatory issues.

  GAPS :

  Regulatory issues must be facilitated.

• Cost of developing new or improved diagnostics and their validation

  Very high costs if the new product is intended for the whole EU market (need for authorization) or other markets in the world.

  There are many commercial platforms in the human arena that could be adapted for use at the pen-side for APP and other members of the PRDC. Also ones, as indicated above, that have been described but not commercialised. Part of the problem with diagnostic tests at the pen-side relate to stability of the tests. They might work in the lab, but not when translated to the field. Also what is meant by pen-side can vary from country to country. For example, the UK has many outdoor units compared to most other countries. Pen-side in that case is in the open field whereas pig units will have rooms to do simple tests (i.e., have a power socket). Head to head testing of such devices is also complicated as many farms use different diagnostic labs even for APP.

  GAPS :

  Regulatory issues must be facilitated.

  Need for standardised head-to-head testing across different pig production units.

• Research requirements for new or improved diagnostics

  Some core funding of pathogenesis groups on host as well as microbiome level was performed.

  GAPS :

  Need for greater funding to support whole genome sequencing and bioinformatics analysis not only for surveillance purposes but also for host/pathogen interaction studies.

  Need more on farm diagnostics to have a better understanding when levels of the pathogen rise and antimicrobial treatments are required to prevent long term metaphylactic treatments.

• Technology to determine virus freedom in animals

  Combination of different methods is used to determine freedom in animals from APP (e.g. tonsillar scrapings analysed by apxIV-gene based PCR in combination with ApxIV-ELISA), but sensitivity is not sufficient.

  GAPS :

  Need for core funding of pathogenesis groups.

• New developments for vaccines

• Requirements for vaccines development / main characteristics for improved vaccines

  Worldwide some core funding of pathogenesis groups and groups studying the genome of the bacterium and identifying the virulence factors, which determine carrier ship and re-exacerbation, exist. It was shown, that a hfq mutant was attenuated for infection of the wax moth as it was in pigs. (Pereira et al. (2015): Galleria mellonella is an effective model to study APP infection. Microbiology 161:387-400).

  GAPS :

  Live marker vaccines (GMO or other) that are efficacious after one application and not counteracted by MDA would be ideal.

  There is need for the identification of those pathogenicity factors that are more relevant, and that allow reasonable protection of animals.

  Effective models alternative to pig and mouse models for testing APP mutant strains as well as the effect of antimicrobial substances and naturally occurring antibacterial peptides onto the pathogen should be developed.

  The identification and standardisation of correlates of efficacy for different types of vaccine are necessary.

  Alternative models of pathogenicity and vaccine efficacy as rapid screens before testing in the pig are necessary.

• Time to develop new or improved vaccines

  From day 0, at least 10 years.

• Cost of developing new or improved vaccines and their validation

  Unknown.

• Research requirements for new or improved vaccines

  No new vaccines are expected.

  GAPS :

  World-wide more core funding of pathogenesis groups and groups studying the bacterium`s genome and identifying the virulence factors is needed.

• New developments for pharmaceuticals

• Requirements for pharmaceuticals development

  No new pharmaceuticals are expected.

  GAPS :

  More core funding of pathogenesis groups, groups studying the bacterium's genome and identifying the virulence factors, and groups studying APP's (molecular) epidemiology in genome of the bacterium and identifying the virulence in the population is needed.

• Time to develop new or improved pharmaceuticals

  Unknown.

• Cost of developing new or improved pharmaceuticals and their validation

  Unknown.

• Research requirements for new or improved pharmaceuticals

  No research ambitions on new pharmaceuticals targeting APP are known.

  GAPS :

  Core funding of pathogenesis groups and groups studying the genome of the bacterium and identifying the virulence factors is needed.

Disease details

• Description and characteristics

• Pathogen

  Actinobacillus pleuropneumoniae.

• Variability of the disease

  There are 19 serotypes of APP with serotypes 1-12 and 15-19 belonging to biotype 1 (Bosse et al. 2018, Soto Perezchica et al. 2023, Stringer et al. 2021).

  Further typing of APP can be done based on requirement for nicotinamide adenine dinucleotide (NAD), with NAD-independent (biovar II) isolates possessing a full length functional nadV gene, whereas this gene has been truncated in the more prevalent NAD-dependent biovar I isolates. Serotypes 13 and 14 were mainly the “atypical” biotype II (no requirement of NAD). Biovar II isolates of serovars 2, 4, 7, 11, 13, and 17 produce only ApxII, whereas isolates of serovar 14 produce only ApxI.

  Historically, APP typing has been performed serologically. However, this can lead to ambiguous results due to shared capsular and lipopolysaccharide O-antigen (LPS O-Ag) epitopes between serovars. Thus, there has been a shift towards the use of molecular serotyping of APP. Previously, two multiplex PCR (mPCR) assays were developed, APP-mPCR1 and APP-mPCR2, for comprehensive typing of all 19 known serovars, targeting serovar specific cps genes for each, However, the cps loci for serovars 9 and 11 are almost identical, differing by only a single base in the cpsF gene, so cannot be differentiated. As these serovars also share the same O-Ag locus and Apx toxin profile, they can be considered as a hybrid serovar 9/11.

  The distribution of APP serotypes is highly variable in space and time. Serotype 18 so far was only found in Europe. This shows clearly, that some serotypes are present as biotype I or II and that their distribution is different on the continents. In a recent study in northern Italy, serotype 9/11 was the most prevalent, followed by serotype 2. 89.2% of isolates belonged to biotype I. Approx. 70% of serotype 13 isolates belonged to biotype II as well as few serotypes 2 and 3 isolates (Guarneri et al. 2024). In the Czech Republic, Germany and Spain serotype 2 is most commonly isolated (Schuwerk et al. 2021). In recent years in Switzerland, approx. 7% of strains belonged to serotype 9/11, with the most common serotypes being 7 and 12 (Matter et al. 2007). Serotype 5 is common in Korea and Canada. Indeed, in the latter country serotypes 7 and 5 are highly predominant (Lacouture et al. 2024). The predominant serovars in Australia are serovar 1, 5, 7 and 15 (Turni et al. 2014 ).

  Several virulence factors have been described. Of high importance are Apx toxins varying in cytotoxity, haemolytic activity and distribution among different serotypes:

  Apx I is strongly haemolytic, strongly cytotoxic and occurs in serotypes 1, 5, 9, 10, 11, 14, 16.

  Apx II is weakly haemolytic and moderately cytotoxic and occurs in all serotypes except 10 and 14. There are a few clinical cases since 2015 with atypical APP serotype 3, for which the ApxII target could not be detected by PCR for typing following established protocols (Frey et al. 1995). Apx III is non-haemolytic, strongly cytotoxic and is found in 2, 3, 4, 6, 8 and 15. Apx IV is produced by all serotypes in vivo and is widely used for diagnostics. It had been shown, that the insertion element ISAp11 can impede apxIV toxin expression and affect the detection of APP. infected animals (Tegetmeyer et al. 2008). There have been exceptions to the toxin profile among serovars. Australian strains of serovar 15 lacked the apxIICA gene by PCR, one strain of serovar 1 and serovar 7 lacked the apxICA and apx1BD respectively (Yee et al. 2018) and North American serotype 2 strains do not produce ApxIII (Gottschalk and Broes 2019).

  Virulence differences between different serotypes are only partly explainable by Apx toxin patterns. Serotype 8 strains have toxin pattern of moderate virulent and could be considered “mild” based on its toxins combination, but is actually the most virulent variant of APP in the UK (Li et al. 2016). Serotype 7 produces ApxII only but it is the most commonly serotype recovered from diseased pigs in Canada (Lacouturebet al. 2024). The organism also produces a variety of other defensive products including an IgA protease, outer membrane proteins, polysaccharide capsules and fine and coarse fimbriae and iron binding proteins.The variability of the disease depends very much, but not exclusively on the strain and its ability to produce toxins and to a large extent on the susceptibility of the animal to develop clinical signs at the time of infection. Up to 6 different serotypes have been found in 1 herd (mostly healthy carriers). In endemic herds the course of disease can be complicated by primary infections with Aujeszky disease virus and Mycoplasma (M.) hyopneumoniae as well as immuno-suppressive disorders. Disease can be complicated either by primary infection with influenza virus (Rodrigues da Costa et al. 2020). However, a primary infection by PRRSV seems not increase the severity of pleuropneumonia (Ferreira Barbosa et al. 2015). In the presence of immunosuppressive virus infections (PCV-2, PRRS) APP strains of lower virulence can cause severe clinical cases. APP infection and disease is frequently complicated by infection with M. hyopneumoniae and Pasteurella multocida.APP is a formidable bacterium for the host defences to combat and this explains why the infection with APP is often found as hyper-acute and acute syndromes associated with sudden death.In animal infection experiments innate immunity was found to be very important with regard to natural resistance of pig breeding lines (Hoeltig et al. 2009). Several Quantitative Trait loci (QTL) were found to be connected with disease susceptibility in these animal trials (Reiner et al. 2014a). Candidate genes involved in iron acquisition from porcine transferrin or LPS-binding were supposed (Reiner et al. 2014b). These findings lack field application and corresponding field observations so far, so that the practical implication is not given so far.

  In the past APP diagnostic has been complicated by presence of Actinobacillus (A.) porcitonsillarum, which has almost identical biochemical and phenotypic profiles. A. porcitonsillarum can produce and secrete ApxII (Kuhnert et al. 2005). Now there is a PCR for A. porcitonsillaris, so that the risk for misidentification is reduced.

  GAPS :

  New serotypes must be identified and characterized if needed and untypable or untypical strains should be referred to a reference lab. Reference labs should be identified. It should be feasible to get data for any unusual isolates in order to detect new serovars or variants with mixed cps and cps loci and apx-profiles (To et al. 2024).

  Some serotypes may be present as biotype 1 or 2 and should be further characterized. A correlation between biotype, serotype and virulence exists, but it cannot be extrapolated from one country to another or from one region to another one. There are more and more exceptions of serotype, biotype and apx-profiles (by PCR) and different combinations in the US, Canada and Europe, and a lack of knowledge how these strains arise.

  There is a lot of variability of the disease depending on the serotype and the geographical origin. This should be further analysed. Examples: serotype 2 strains are highly virulent in Europe and almost non virulent in North America (they lack one toxin). Serotype 4 strains are highly virulent in Spain but rare and non virulent in Canada. Serotype 15 is only highly important in Australia, although a recent outbreak was reported in USA (Machado et al. 2024). A general assumption of virulence cannot be done. In addition, the same strain can be highly virulent or low virulent depending on the herd and other infections. In a vaccine trial serovar 15 caused only mild disease in the infected animals yet on farm it lead to high level of mortalities.

  Proofs have also been done with strains of serotype 1 and 9 (experimentally infected animals). Herd factors and host factors (innate immunity, genetically determined reduced natural susceptibility) have to be studied.

  Need for epidemiological approaches to understand serotype prevalence and dynamics at a time point, at the country, region or even herd level. It seems that the prevalences change over time, and more or less pathogenic clones fill the gap left by pre-existing serotypes in an area. This has been the case for biotype 2 serotypes in some areas in Europe and for serotype 1 in Korea.

  Associations of disease with change in breed or breeding company herd origin should be studied.Serotyping must be achieved in most countries (strains isolated from diseased animals) to have more data. Data on serotype distribution for most swine-producing countries are not available (some data were more than 25 years old). With the arrival of PCR serotyping there is no need of using animal sera, so that any lab may be able to serotype strains, but the work must be financially supported.Further research on APP serotype 12 is needed. Since this serotype has a low pathogenicity, it is interesting to study the immunity created by this organism.

  Apx toxin expression in newer serotypes need to further be analyzed.

  Atypical APP isolates/strains (e.g. no ApxII expression in serotype 3) should be analysed in more details.

  Insertion elements (ISAp11) can impede apxIV toxin expression. This mechanism should further be analysed in vitro and in vivo.

  The variability of the pathogen and the disease in conjunction with other factors (PRRSV, SIV, PRV, PCV2, Pasteurella multocida etc.) has to be investigated more intensively on individual pig level, as well as on population/herd level. Many practitioners believe (mainly in Europe) that PRRS/APP association does exist and is important. Both pathogens are involved in development of pleuritic lesions (Fablet et al. 2012). The pathogenesis of coinfection with other respiratory pathogens, especially with PRRSV, M. hyopneumoniae, Pseudorabies Virus and SIV or PRCV has to be further studied, as literature shows, that clinical episodes are preceded by an infectious / non-infectious trigger (Klinkenberg et al. 2014; Rodrigues da Costa et al. 2020; Merialdi et al. 2012).

  APP should be studied in the ecology of the upper respiratory tract / oral cavity to understand phenomena as colonization, carriership and interaction with the host, eventually resulting in translocation of the bacterium to the lung, which will lead to (pleuro)pneumonia.

  Knowledge on specific APP genes required for poly infections (e.g., APP-influenza, APP-PRRSV) are necessary to unrevel pathomechanisms of coinfections.

  In Haemophilus (H.) influenzae, specific genes were identified that were required for survival when the host suffered from H. influenzae-influenza infections. Given that APP is often part of PRDC – a gap is also whether specific genes of APP are required for survival when the infection is mixed with viral infection (or even other bacteria).

• Stability of the agent/pathogen in the environment

  It is relatively delicate but is capable of surviving for at least 5 days in nasal discharges at 18 degrees. It is very sensitive to drying, but can survive for at least 30 days in water at 4 degrees centigrade. It resists a long time in an affected lung and also remains viable in frozen tissues. Normally it only lives in the nasal cavity and in the bottom of tonsillar crypts and nasopharynx. There has been a report, that viable APP. is present in the drinking water of swine farms and may use biofilm as a strategy to survive in the environment (Loera-Muro et al. 2013).

  GAPS :

  Survival of APP in the environment in various substances outside the pig should be further investigated. Survival of APP on the pig skin, pen floor and pen construction as well in air should be investigated.

  Different types of pig production units should be investigated, because they have different risks. This might have implications for depop-repop strategies.

  It should be investigated what genes are responsible for survival in the environment – as they could form the basis of targets for prevention/killing.

  Follow up studies and validation of survival in water or biofilms in farms should be performed.

  Survival of APP in the natural environment in pig pens versus aerosols should be examined. Recent data with other bacteria suggests that survival in aerosols requires particular traits/genes. We know that aerosol transmission is lower than between pigs in pens, so different mechanisms apply. Transposon mutagenesis experiments could also identify genes that are more important in the different environments. With M. tuberculosis, the transcriptome profile of bacteria in aerosols is different to that in sputum. It should be examined if something similar occur with APP and what are the effects on transmissibility.

• Species involved

• Animal infected/carrier/disease

  All pigs can be infected, including wild boar and feral pigs. Pigs may carry small numbers of bacteria in the tonsil. The tonsils can be a reservoir with APP forming biofilms (Fittipaldi et al. 2003; Aper et al. 2020), serving as a reservoir of the bacterium on farms. Treatment of APP with dispersin B (disruptor of biofilms) enhanced the sensitivity of APP to ampicillin (Hathroubi et al. 2017).There is a small chance that pigs suffer from septicaemia, when they become stressed. It is not clear, if septicaemia with APP is only exceptional or if it still remains undetected, because nearly no other organs than lung will be affected in the end. It remains in most cases a respiratory disease. It is reported that APP can spread regularly to the whole body by bacteriaemia during the acute phase of infection. It can be found at the pleura and pericardium but also in liver, kidney and meninges without causing any histological tissue alterations (Hoeltig et al. 2018).After infection bacteria can be excreted in large numbers, but this does not necessarily have to result in faster transmission (Tobias et al. 2013).Pigs can be carriers without building up any currently detectable humoral immune response. Carrier pigs can develop disease even with previous immune response to heterologous strains in stress situations.

  GAPS :

  For the assessment of medication as an additional control measure, it is important to establish a relationship between treatment and tonsil colonization, as well as the concentration of antibiotics in the tonsilar tissues. Sufficient strategies for treatment in order to eliminate carrier status would be important.

  As biofilm formation is possible; what is the role, importance, impact of biofilm formation for the epidemiology, treatment, eradication etc. is not known so far. No experiments in pigs have investigated mutants in biofilm formation to determine their role during acute or chronic infection. Only in mice similar experiments were performed.

  There is a gap in understanding the transmission of APP generally and specifically transmission from sows to its offspring in the farrowing room. There is no knowledge how one can intervene on this sow-offspring transmission, e.g. with (non-) antimicrobial substances or vaccination.

  It is not known what genes are required for long term colonisation in tonsils and lungs. Transposon mutagenesis like experiments have only been done for acute infection. In former SCOTS experiments anaerobic genes were shown as being important for long-term (40 days) colonisation. This approach should be performed on a genome-wide basis, because the technology to do that is now in place.

  In this field, recent results in dentistry suggest that although antibiotic treatment affects oral microbiome for a short period, after 1-2 weeks the original microbiome is restored. It is not known, if porcine oral microbiome will be restored in the same way.

• Human infected/disease

  Only one report is known about human infection. In this potential case an APP. mutant was injected accidentally into a thumb (Rycroft et al. 2011).

  GAPS :

  N.A.

• Vector cyclical/non-cyclical

  None reported (mice can be infected experimentally but no real evidence as to their ability to infect pigs on the farm).

  GAPS :

  If APP survives in water, there is a possibility that they may also survive in amoeba – as many other Gram-negatives. If APP survive in amoeba or similar organisms on farms when in water should be investigated.

• Reservoir (animal, environment)

  Probably none other than pigs, because of some host specific systems (e.g. iron binding). However, a study in Slovenia showed that more than 50% of wild boars were seropositive to APP, hence suggesting a possible spill over or reservoir (Vengust et al. 2006).On farm reservoir have been established, such as the survival of APP in drinking water in multi-species biofilms (Loera-Muro et al. 2021).

  GAPS :

  Prevalence studies in wild boars to investigate their possible role as reservoir in every pig-producing country. In general, the presence of APP. in wild boar and the risk for transmission to farmed pigs should be assessed.

  Further studies on biofilms as reservoirs in the environment of pigs need to be done.

• Description of infection & disease in natural hosts

• Transmissibility

  Spreads pig to pig particularly by direct oral/nasal contact (solid pen partitions on 1.50 m are always a help to prevent direct transmission) or by droplets within short distances. It has been shown experimentally that the agent only travels 1-2 metres in an aerosol. Although some epidemiological observations suggest aerosol transmission on longer distances (Desrosiers and Moor, 1998). Experimental studies showed, that indirect transmission within a department may be nihil (Tobias et al. 2013).Experimental and field observations defined the transmission rates for APP with direct transmission among pigs to be β=0.06 – 0.1 per day and indirect transmission occurs with β = 0.006 (Tobias et al. 2014; Velthuis et al. 2002).It should be stated, that this is the transmission rate for diseased as well as non-diseased pigs.The acute form of the disease has been observed in fattening enterprises employing batchwise production and enterprises with >1 unit per building (often 4 units filling one unit up every 4th week) are more at risk. There were records about problems also in fattening enterprises, which belong to the same multisite production systems with only one age category at the site. Fatteners in this system suffered from acute disease in 1-2 batches and thereafter regained healthy as soon as the piglet producing site was healthy.

  GAPS :

  Transmission of the agent among pigs mostly occurs without the development of any clinical signs. The reasons for that and the impact of transmission for increase in carrier pig rates should be elucidated.In general there is a lack of knowledge on different transmission routes and prerequisites of APP for specific routes of transmission.

• Pathogenic life cycle stages

  Although it is considered a primary pathogen of pigs (may induce disease without the intervention of any other organism), in total the risk for becoming diseased by APP may have been decreased in some regions by vaccination for mycoplasmosis (less lung damage to colonize), and vaccination for PRRS and PCV2 (reduced immuno-suppression).

  GAPS :

  The influence of PRRS/PCV vaccination on APP transmission as well as clinical outcome on pig farms should be investigated. PRRS/PCV2 active infection on APP response to vaccination should be studied. Investigation of SIV (as primary viral pathogen in PRDC) vaccination and APP transmission should be further investigated, especially since the dynamics of influenza virus on farms has changed considerably. Influenza virus can circulate subclinically already in very young pigs in some cases, whereas in others IAV may function as ‘trigger’ and cause severe disease at first, with bacterial complications later, due to, amongst others, APP. Interaction of other bacterial pathogens and influences of these on severity of disease should be considered. APP might benefit from coinfection with S.suis in the lung (de Buhr et al. 2019).

• Signs/Morbidity

  Hyper-acute APP: pigs are found dead with no clinical signs but often a cyanotic carcase. Can occur suddenly in the lairage at an abattoir if there is considerable stress or delay in slaughtering for over 24 hours.Acute outbreaks: Usually non-immune animals with mortality 15-20%, depression, anorexia, pyrexia, dyspnoea, cyanosis and death within 4-6 hours. Clinical signs are most common in the finishing phase after 12 weeks of age. Maternal immunity may protect pigs til that age but exceptions with earlier occurrence do exist.Sub-acute: anorexia, fever, respiratory distress, prostration, coughing, exercise intolerance, and lesser but variable mortality.Chronic: pigs have survived but have large areas of lung damage and may remain dyspnoeic and fail to grow. They should be culled if no improvement after 2-3 days in a hospital unit with treatment with parenteral antibiotics.Possible role in chronic pleuritis, often without (significant) pneumonia and clinical symptoms and frequently observed at slaughterhouse inspection supposed, but not unambiguously proven.Animals subclinically infected may remain seronegative and clinically healthy.

  GAPS :

  Chronic infections sometimes are present without previous acute infections; signs are sometimes difficult to observe, but there are demarcated lung lesions at slaughter. There is also very often a sub-clinical infection.For this reason, the conditions (age and other host factors and bacterial factors/virulence factors as well as environmental factors) for the development of subclinical carrier status without preceding clinical symptoms must be investigated. The mechanism for some kind of age resistance is needed. In many cases in which older animals (e.g. sows) are infected, clinical signs may be very unnoticeable (considering the lesions at necropsy) whereas in very young pigs (offspring) severe clinical signs may be noted.

• Incubation period

  Can be as short as 12 hours after stress, such as occurs in lairages. It likely depends on the initial colonization state and may be on the infectious dose and virulence of bacteria and subsequent stress. All the usual causes of stress-weaning, mixing, moving, re-batching, transport to lairage and killing 24 hrs later will predispose to disease. Pigs on slats in winter may be more susceptible due to chilling of the chest wall, in general any climatic disorders (low temp in general, extreme temperature changes day and night, draught, high ammonia and or CO2 and others) will shorten the incubation time. In general, stress may contribute to disease, but it is not essential. Infection with (super)virulent strains needs no additional factors for disease development. Studies on APP exposure to adrenalin or noradrenalin has shown that bacteria are susceptible to host stress hormones and may be provoked to express toxin producing genes or biofilm formation genes (Li et al. 2012; Li et al. 2015).

  As it is possible that infected animals will not develop clinical signs at all, the incubation period can be a lifetime, and for this reason, it is extremely variable.

  GAPS :

  The influence of specific stress factors (also named triggers) on the incubation period and pathogenesis of APP clinical outcome should be investigated, as suggested (Klinkenberg et al. 2014). Because the immune and nervous system are tightly interlocked, host stress responses will influence the pathogenic outcome of bacterial infection. In farm animals, there is a lack of knowledge on this interface, which is very important for infection medicine and animal welfare. Well accepted checklists for detection and feasible interventions of triggers on farms seem to be needed.

  Strain-specific differences and breed-specific differences in the incubation period overlap and should be investigated. More importantly the general concept of colonisation and disease induction should be studied.

• Mortality

  May be none, if endemic, but here may be high culling rates. Usually in hyper-acute and acute outbreaks in susceptible naïve pigs usually following concurrent viral disease or importation of carrier pigs there may be 10-25% mortality or more.

  GAPS :

  Mortality is only the tip of the iceberg, the most challenging issue is recognizing by direct or indirect methods those animals that are suffering from APP-related pneumonia. These pigs are not performing well because of a suboptimal respiratory function. It would be very useful to have available tools to “select” and segregate affected and non-affected animals to establish an intervention.More than mortality, morbidity has a high impact on animal welfare and economic impact. The focus on mortality distracts from the necessity to increase knowledge on the disease to decrease the impact on animal welfare and economics.

• Shedding kinetic patterns

  Shed continuously from infected pigs in coughing, but the transmission is also observed without clinical signs. Subclinically colonised pigs can transmit APP with β = 0.06 among pigs. Although clinically affected pigs may shed more bacteria, transmission may be even less efficient (Tobias et al. 2013).

  GAPS :

  Ways of transmission as well as transmission rates in animals not showing clinical signs like coughing, should be investigated in more depth.

• Mechanism of pathogenicity

  Pathogenicity requires nose to nose contact, or exchange of oral fluid and attachment to the tonsil. APP bacteria remain deep in the crypt of the tonsil. Organisms may then be aerosolized and located in the caudal lobes of the lung, where there is believed to be a higher oxygen tension. The organisms attach to the alveolar epithelium via the fimbriae and protective IgA is broken by proteases of APP. The tissue damage results in the production of a lot of Il-1, Il-6 and TNF alpha which increases the inflammation. The toxins ApxI and III can kill macrophages within 30-60 minutes while the APP capsule prevents phagocytosis. Transferrin-binding proteins are expressed in the acute stage of the disease and downregulated in the chronic stage, so that iron acquisition is done by various mechanisms. The bacterial colonies increase and can be seen as micro-colonies in the lung and trachea. The toxins can produce this effect within 3 hours of infection. Capillary congestion results followed by oedema, which leads to distension of lymphatics and septae in the lung. The necrosis then spreads and sequestrate may follow until it is walled off by fibrin. There is also arterial thrombosis and possibly septicaemic spread to joints or bones. It is unclear if septicaemia is exceptional and does not occur in most of the cases, or if it often happens and stays only undetected during the early stages of infection.Host factors, especially genetically determined factors of the innate immune system are decisive for the outcome of the disease.

  GAPS :

  The reason of caudal lung lobe affection should be studied. Are there specific receptors located only in these lobes, or is it a stochastic process of inhalation of larger particles?

  The variability of pathogenicity highly depends on breeding line specific and individual differences in the innate immune system. More information on genetic determined host susceptibility for porcine pleuropneumonia is necessary.

  The different gene expression patterns of APP in acute and chronic stages of disease as well as under anaerobic (sequestrate) and aerobic conditions must be investigated.

  Although Apx toxins I and II are recognized as highly harmful to lung tissue, some serotypes of APP only excrete toxin II, but lesions are indistinguishable from those produced by more pathogenic serotypes. It is important to look into the pathogenic action of other bacterial factors that synergise with cytolytic and hemolytic toxins. As an example: serotype 7 and serotype 12 produce the same toxins. However, serotype 12 is of low virulence and serotype 7 is responsible for almost 40% of clinical cases in Canada.

• Zoonotic potential

• Reported incidence in humans

  Only one report known: in this potential case an APP mutant was injected accidentally into a thumb (Rycroft et al. 2011).

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

  Not likely.

• Symptoms described in humans

  None described.

• Likelihood of spread in humans

  Unlikely, and not reported.

• Impact on animal welfare and biodiversity

• Both disease and prevention/control measures related

  Chronic disease in endemically infected herds can result in disease related reduction of growth performance and impaired animal welfare. Control and prevention through biosecurity and vaccination are necessary. If antimicrobial substances are used on a farm to fight the disease, this can induce bacterial resistance to antibiotics, which must be avoided.

  GAPS :

  Environmental factors, especially avoidance of crowding, climate control and right stocking density, are important preventive measures that should be investigated systematically. Control of other respiratory pathogens can reduce frequency of chronic cases in endemic infected herds.

  Further improvements on vaccines and vaccination schedules in combination with treatments, and building of facilities and cleaning and disinfection procedure that diminish pathogen pressure are needed.

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

  Occurrence of disease in wild boars.

  GAPS :

  The geographic distribution of serotypes in wild boars as a wild species reservoir of this pathogen should be examined.The geographic distribution of serotypes in wild boars as a wild species reservoir of this pathogen should be examined.

• Slaughter necessity according to EU rules or other regions

  No, unless welfare cases in chronic stages not responding to treatment.Pleuritis requires stripping the lungs from the carcass, which is extra work and may depreciate part of the carcass. APP can cause this pleuritis, especially in the caudo-dorsal part of the lungs. A pleuritis score or score on dorsal pleuropneumonia given at the slaughterhouse can be used as a marker for APP herd problems (SPES system). For experimental APP infection a multiple lesion scoring system was developed (Siblia et al. 2014).

  GAPS :

  A pleuritis score or dorsal pleuropneumonia score given at the slaughterhouse should be validated as a marker for APP herd problems and if it can be used as the basis for decision making on therapy and prophylaxis (Maes et al. 2023).

• Geographical distribution and spread

• Current occurence/distribution

  Worldwide but different serotypes and variants in different countries.

  GAPS :

  Reports of shifts in serovar prevalence in some countries indicate the need for regular seroprevalence surveys.

• Epizootic/endemic- if epidemic frequency of outbreaks

  Endemic but will occur as an epizootic in individual herds due to lack of previous exposure and new arrivals carrying the disease. Economically more important is the endemic situation.

• Speed of spatial spread during an outbreak

  If acute, there is a high incidence of pigs with pleuropneumonia spread spatially in space within the same compartment. Pigs without adaptive immunity to APP are highly susceptible to developing clinical signs. Stock that has never been exposed to APP may not have developed immunity and thereby the disease may seem to spread fast. However, it is unknown if the bacteria are actually spreading slowly or if the trigger causes disease in subsequent individual pigs in a relatively short period of time.Transmission is observed from sub-clinically infected pigs to susceptible pigs. The transmission speed is variable with studies showing β= ~0.05-0.1 newly infected pigs per day by one infected pig even in pigs without adaptive immunity to APP. (Tobias et al. 2014; Velthuis et al. 2002).

  GAPS :

  Factors which influence the speed of transmission (host factors, environmental factors and strain characteristics) should be investigated.Although some of the factors are known, it is not known, how to slow or stop transmission.

• Transboundary potential of the disease

  Likely to spread by pig to pig contact, possible role of international trade of live animals.

• Route of Transmission

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

  Transmission is pig to pig with β= ~0.05-0.1 newly infected pigs per day by one infected pig. Possibly also infected organic material contaminated by discharges.

  GAPS :

  Transmission rates can vary between serotypes and strains. Bacterial characteristics decesive for transmission rates should be investigated.

• Occasional mode of transmission

  Aerosol transmission is a possibility, but experimentally, and in pig barns difficult to detect transmission over distances of over 1-2 metres. Reports confirm the very low indirect transmission rate of β< ~0.006 between pigs in different pens (Tobias et al. 2014) and no indirect transmission under experimental conditions (Tobias et al. 2013).

  Some epidemiological observations suggest sequential episodes of clinical disease, which were hypothesised to be due to transmission over longer distances (Desrosiers and Moore, 1998).In practice, the acute form of the disease has been observed in fattening enterprises employing batch-wise production but with >1 unit per building (often 4 units filling one unit up every 4th week). There are reports about problems in fattening enterprises belonging to the same multisite production systems with only one age category at the site. Fatteners suffered from acute disease in 1-2 batches and thereafter regained healthy as soon as the piglet producing site became healthy again.

  GAPS :

  Modes of indirect transmission should be studied and quantified, to quantify risks of transmission by different means on farms and act upon it.

  Transmission from mother to offspring should be studied more in detail (when, by what excreta, and how to influence it) in order to design effective interventions.

  APP has been shown to be present in drinking water; the importance of this finding for transmission should be elucidated.

  Identification of APP genes that have a role in transmission need to be identified. In general there is a lack of knowledge on different transmission routes and prerequisites of APP for specific routes of transmission.

• Conditions that favour spread

  Generally speaking, suboptimal rearing conditions favour spread of disease. More specifically, any animal population under stress; weaning, mixing, moving, overcrowding, transport, and in particular chilling on slats in winter and water deprivation may induce clinical episodes in populations with insufficient immunity, especially if rapid changes in ambient temperature and high humidity paired with insufficient ventilation occurred.

  It may seem as if these conditions favour spread, but it is not sure that they really favour the spread of the pathogen or induce clinical signs in a in higher proportion of pigs present.

  Furthermore, as there is heterogeneity in transmission from sows to its offspring during suckling (Tobias et al. 2014b), any practices that include mixing of litters during suckling or after weaning will result in increased proportions of infected (colonized) pigs (Tobias et al. 2014a).

  GAPS :

  The effects of stress conditions on the pig immunity in relation to APP. transmission may be further investigated, because it is not clear, if adverse conditions truly increase transmission.

  The patho-biological mechanism of how these predisposing conditions cause APP to induce clinical signs should be elucidated (Klinkenberg et al. 2014).

  The effects of stress conditions on the pig immunity in relation to APP. transmission may be further investigated, because it is not clear, if adverse conditions truly increase transmission.

  The patho-biological mechanism of how these predisposing conditions cause APP to induce clinical signs should be elucidated (Klinkenberg et al. 2014).

• Detection and Immune response to infection

• Mechanism of host response

  At the primary exposition of the lungs severe host response with mortality or severe lung pathology, lung necrosis that never fully heals and leaves collapsed lung and ultimately pigs with pleurisy that have dyspnoea and may have to be culled may occur.In endemic situations pigs produce antibodies to a wide range of bacterial products, such as lipo-polysaccharide, capsules, fimbriae, and outer membrane proteins. These antibodies occur as IgA in the upper parts of the tract and both IgA and IgG in the lower parts of the tract. These antibodies block the toxins and allow phagocytosis.Maternal antibodies may last up to two month depending on the amount of acquired colostral antibodies (Vigre et al. 2003), but generally 4-6 weeks. Active antibodies start at about 5-10 days post infection of the lung and appear to peak 3-4 weeks after infection. Mere infection of the tonsils may occur without induction of an immune response (Chiers et al. 2002). Immunity to homologous strains is probably lifelong but the protection against other strains is probably not good. There is some evidence that serotype 2, which does produce Apx II, III, and IV may provide protection to other strains. Carrier animals often do not mount an immune response.

  The innate host immune responses, are very important for the outcome of disease. The acute phase response to APP has been assessed in a couple of studies (Gómez-Laguna et al. 2014; Heegaard et al. 2011). In addition, papers describing the host transcriptome of APP-infected lungs have been published (Zuo et al. 2013; Brogaard et al. 2015).

  GAPS :

  It is necessary to deepen the knowledge of the pig-specific immune response against the bacteria. Although the immunogenicity of the Apx toxins have been demonstrated, vaccines possessing these recombinant molecules and other bacterial components do not provide complete protection. The possibility of using live attenuated vaccines has been also explored, but no studies of efficacy against various genotypes and antigenic types or large-scale studies that demonstrate efficacy and safety are available.

  There is a lack of knowledge about specific factors of the innate and especially mucosal immune defence mechanisms and their stimulation by specific vaccine components and adjuvants.

  Greater use of publicly available transcriptome data to drive APP -specific diagnostics

  There is a lack of knowledge of the oral microbiome, metabolome and resistome of pigs and how known pathogens, such as APP, survive and interact with this ecology. The oral microbiome should be mapped and associations with APP transmission and clinical outcome should be studied.

• Immunological basis of diagnosis

  Pigs produce antibodies to a wide range of bacterial products, such as lipo-polysaccharide, capsules, fimbriae, and outer membrane proteins. These occur as IgA in the upper parts of the tract and both IgA and IgG in the lower parts of the tract. These antibodies block the toxins and allow phagocytosis. Maternal antibodies mostly last 4-6 weeks but can also last longer (7-8 weeks). It is unknown what specific APP antigens are recognised by maternal antibodies that protect in the first 6-8 weeks.Active antibodies start at about 5-10 days post infection and appear to peak 3-4 weeks after infection. Immunity to homologous strains is probably lifelong but the protection against other strains is probably not good. There is some evidence that serotype 2 which does produce Apx II, III, and IV may provide protection to other strains.

  GAPS :

  The immunological basis of diagnosis is not sufficiently investigated and understood.Not all infected animals produce detectable levels of antibodies. Most carry the bacterium in their tonsils.

  The biggest challenge to perform ante-mortem diagnosis by serological techniques for antibodies, is the great diversity of serotypes, and the existence of other bacteria that mimic APP. It would be desirable to develop techniques based on serotype or serogroup-specific antigens to avoid cross-reactions and facilitate the interpretation.Need for alternative antibody (or other)-based diagnostics to replace or be used in combination with ApxIV for routine herd surveillance, especially point of care-based tests.

  Specific APP antigens, which are recognised by maternal antibodies that protect in the first 6-8 weeks, should be analyzed.

  Specific tests for innate immunity or cell mediated immunity are lacking.

• Main means of prevention, detection and control

• Sanitary measures

  Not very effective as the main pig-to-pig transmission is by direct contact, hence requires importation of clean stock, cleaning and disinfection of sheds, because the agent will survive for longer outside the pig than it has been able to prove. Recent reports suggest survival in water (Assavacheep and Rycroft 2013).Strict separation of age groups, no mixing also not just after birth and no contact between different age groups look promising as a vehicle to prevent transmission. All in-all out technology is highly effective in controlling (reducing) disease. Avoiding exposure to cold climatic conditions, like chilling conditions and huge temperature fluctuations is of paramount importance to reduce the occurrence of clinical outbreaks in endemically infected herds.In M.hyo positive herds, M.hyo vaccination plays a role in protecting against APP out-breaks. PCV2 vaccination and Aujezky vaccination (positive countries) plays also a big role in preventing APP out-breaks.

  GAPS :

  Because the carrier pigs will carry the bacterium in the tonsils and/or bucca, sensitive sampling and detection methods must be developed further. Tonsil scratch samples can be used for detection and typing (cps- (serotype) and apx-toxin-profile, but RTU kits are not commercially available (Tobias et al. 2012).

  Oral rope testing for pen wise testing gives reliable results of presence of the pathogen, but essentially detects APP that colonise in the upper throat and do not necessarily cause disease.

  PCR assays have been developed for demonstration of APP in tonsils of pigs, however a negative result does not necessarily imply that the tonsils are not colonized since the bacterium can enter deep in the crypts.

• Mechanical and biological control

  The main control is importation of clean stock (free of APP.) with quarantine and isolation and possible use of sentinels, biosecurity, reduction of stress, provision of ad lib clean water supplies and if necessary, where culture of the organism has been achieved, metaphylactic use of antibiotics in water or feed. This procedure may no longer be allowed or recommended in all countries. Metaphylactic should not be considered a preventive measure as it does not guarantee, thar APP will be eliminated from infected pigs. Individual carriers are often the problem.

  GAPS :

  On infected farms knowledge is needed how to control the occurrence of triggers / conditions that induce adverse clinical outcome.

  On APP free farms control measures should focus on prevention of introduction of the pathogen (by pigs as it is well known), especially by other (indirect) means.

• Diagnostic tools

  Different techniques are used for the diagnostic of APP in acute and chronic disease as well as in subclinically infected pigs. However, diagnostic tests are not capable of detecting the carrier pigs, which have only a few organisms in the nasopharynx on the individual level. Subclinical animals may not develop antibodies, so as with any antibody-based test, sensitivity at an individual level may not be so high. But at a herd level, antibodies will be produced, especially against LPS (lower levels of antibodies against the toxins, if there is no bacterial replication in the animal). ApxII-ELISA was established in order to detect subclinically infected animals (Leiner et al. 1999), but is not APP-specific as other Actinobaciilus spp. may produce ApxII.

  In general, diagnostic tests include clinical signs, gross post-mortem examination, histopathology with IHC confirmation, culture, and a range of diagnostic tests. For IHC the serotype should be known, because the specific antiserum must be chosen.

  Sequencing techniques can reliably define serotype, apx toxine gene patterns and antimicrobial resistany genes.

  Clinically affected or recovered pigs may be detected by culture of lung tissue or bronchoalveolar lavage fluid and by the presence of antibodies in serum. The detection of antibodies in saliva, nasal secretions, bronchoalveolar lavage fluid, colostrum and meat juice might also be possible but is not performed routinely.Bacterial culture from lung tissue is convenient only during acute infection but difficult in chronic infection or subclinically infected pigs. Culture may use nasal or tonsillar swabs or preferably scrapes with use of sheep blood agar plates together with a staph streak or the use of special media such as chocolate agar or PPLO agar supplemented with NAD. Tonsillar samples usually result in higher sensitivity of detecting colonized pigs but the isolation from tonsils (even worse with nasal swabs or oral fluids) should not be done to diagnose clinical disease since APP may be in tonsils without causing disease (Tobias et al. 2014a; Velthuis et al. 2002).

  In general, the sensitivity of bacterial isolation can be significantly improved by using selective culture media or immunomagnetic separation. For the isolation with magnetic beads the serotype must be known and then the technique has been demonstrated to be highly sensitive compared with normal isolation procedures. (Jacobsen and Nielsen, 1995; Gagné et al. 1998).

  APP may be serotyped by slide agglutination using antibodies to the capsule, by ELISA, co-agglutination, latex agglutination, indirect hemagglutination, gel diffusion or genotyping (by multiplex PCR), using DNA probes and ribotyping. With the arrival of PCR serotyping, serotyping is not any longer dependent on the availability of serotype specific animal sera, so that any lab may be able to serotype strains.Several multiplex PCR assays have been developed for serotyping of all 19 serotypes (Stringer et al. 2021).Agent (specific nucleic acid) is identified by single or multiplex PCR based on ApxIV.

  Primers (and probes) to Apx IV have been developed that will detect all strains of APP. To enhance the sensitivity of detection a real time PCR has been developed that targets the Apx IV genes to be used on tonsillar and nasal swabs with a sensitivity of 5 CFU/reaction (Tobias et al. 2012). An isothermal diagnostic assay targeting the Apx IV has been developed to bring diagnostics to the farm (Stringer et al. 2022).

  Several antigen ELISAs have also been developed, which are mostly based on wall (lipo) polysaccharides (long-chain LPS) or capsular antigens (Dubreuil et al. 2000). Recombinant proteins as antigens, or blocking ELISAs using monoclonal antibodies are also used. Formerly, the CF test, latex agglutination tests, and tube agglutination were used. Most of these tests are more or less serotype specific, because cross-reactions occur. Capsular antigens are not used since contamination with other antigens induce a specificity problem; LPS is used (there are commercial kits available) and another mixed antigen is also used in a commercial kit. LPS based tests show cross-reactions between APP serotypes and may also be cross-reactive with A. porcitonsillarum and A. lignieresii and are moderate sensitive. They are more or less serotype-specific.

  Routinely antibodies are measured by Enzyme-linked-immunosorbent-assays (ELISA) based on toxin detection or LPS (Gottschalk, 2015).It must be kept in mind that related bacterial species such as Actinobacillus porcitonsillarum, A. suis and A. rossii have similar apx genes, so that cross reactions occur between those species with tests based on the ApxII toxin.In positively tested sera a differentiation of serotypes should be performed by a specific LPS-ELISA for specific serotypes and the cross-reacting groups respectively: 1/9/11, 2, 3/6/8, 4/7, 5a/5b, 10, 12.The ApxIV-ELISA with a high specificity for all serotypes of APP (no cross-reactions with other Actinobacíllus species known) is available in Germany since the end of 2012 and 2013 in the USA (Opriessnig et al. 2013). It can be used in combination with commercial vaccines (not having this toxin) in its formulation as a marker for disease in vaccinated animals.ApxIV-based Ab-tests may be false negative by insertion elements.

  The formerly used complement fixation test for serotyping and slide agglutination tests cannot be recommended because of lower sensitivity and cross reactions.

  GAPS :

  Diagnostic tools are unsatisfactory with regard to variability of APP and the similarity to related microorganism, so that tests should be further developed and validated.

  Anti-omlA of serotype 7 together with anti-omlA 1 and 5 could complement the detection of all known serotypes by IHC. Further analyses are necessary.

  PCR based on apxIV gene is useful for all serotypes unless the gene is destroyed by an insertion element (IS) element.

  PCR diagnostics for isolates of all serotypes should be compared to the results of immunodiagnostics, contradictory results should be elucidated.

  All indirect tests have their drawbacks, e.g. atypical strains may arise, and indirect methods such as serology may not detect antibodies to such strains. Therefore, specific methods ought to be developed whenever atypical strains are detected (Example: serotype 12 in Australia that later became serotype 15; Serotype 5 in Sweden, were antibodies are detected in ELISAs based on the type strains 5a or 5b). Antibodies might be only detected when using antigens from the respective atypical isolate. These problems should be further analysed.

  A distinction between APX IV Elisa (not that sensitive) and serotype specific ELISA should be elaborated.The quality of the ApxIV test with regard to its sensitivity and specificity should be determined under different conditions and in different stages of infection. In infected farms this could be achived by sampling animals with different age categories.

  A comparison of quantitative PCR diagnostic performances of sampling coming from different sampling sites (nasal, tonsils…) should be done to identify the best ante mortem sampling site in carrier animals.Even the apx-gene-typing by PCR reveals unpredictable results, e.g. unusual apx-gene profiles, so that further research is needed.New diagnostic methods for identifying the virulence potential of specific strains are essential.

  In addition, there is a need for strain characterization methods more than serotyping, which will be helpful for future control strategies. This could include amongst others WGS based methods.

  Specific monoclonal antibodies for tests (blocking tests) should be developed.

  Diagnostic protocol for ApxIV false positive test results in APP free herds is needed and to be approved by pig trade community and governments.

  A definition of an APP free herd is also needed (based on which tests + frequency and allowed number of false positive test results without losing APP free status).

• Vaccines

  Killed whole culture vaccines have been developed with several serotypes in the vaccine. Whole cultures with adjuvants may produce a lot of tissue reactions. Some sub-unit vaccines have been developed which contain Apx toxoids to I and II and III and the outer membrane proteins. ApxIV is not used in vaccines.At the moment, there are several licensed that contain the Apx toxoids (some in combination with inactivated cells).A live vaccine has also been commercialized in the past.Acellular vaccines have also been produced. A gene deletion marker vaccine has also been tried. Vaccines have been tried for parenteral, aerosol, and intra-peritoneal routes.

  GAPS :

  Vaccines can only prevent the symptoms of the disease. However, they are not effective in preventing APP transmission and are therefore ineffective for eradication since vaccinated and infected animals are still able to shed the organism.Having a vaccine that is able to effectively reduce transmission from pig-to-pig or sow-to-offspring would be a great improvement

  In general the protective effects of all vaccines are still not completely satisfactory. Intranasal vaccines should be studied since they can induce better mucosal immunity by producing secretory IgA.

  Vaccines that target innate / mucosal immunity should be evaluated/developed. This way vaccines may act on the carriership status.

  It seems that only viable bacteria can exhibit full pathogenic action in the recipient pig. Therefore, the live attenuated vaccine would be the best approach to allow the pathogen to attach to the target tissue and allow the host to respond properly. However, several issues should be solved before, such as the interference of antibiotic treatments common in the pig-rearing practices with immunization. The amount of bacteria per vaccine dose seems to be also crucial, and universality still is questionable.

  The use and effect of autogenous vaccines should be investigated, as they are widely used in some countries (e.g. France).

  There is a lack of published data on the best adjuvants for use in pigs whether that be by IM, SC, IN or via aerosol routes.Different Apx toxins display differential regulation by different phasevarions, which brings the use of toxins in subunit vaccine into question.

  The optimal time of administration of different vaccine types (toxoid, LAV, etc) and their effect on maternal antibodies is unknown so far.

• Therapeutics

  If there is a herd problem, then one can medicate with a variety of antibiotics. Curative or metaphylactic medication may prevent death but may not prevent the development of lesions. A wide variety of antibiotics can be used following good practice guidelines including tetracyclines, amoxicillin, ampicillin, penicillins, trimethoprim and sulphonamides,tilmicosin, tiamulin etc. Quinolones are very effective, but should also be used with certain care for several reasons. It has been incidentally suggested, that quinolones could be an alternative at aims of eradicating the microbe from herds. If clinically affected pigs require injection therapy as they do not eat and are reluctant to drink until the pyrexia has disappeared. Then they can be kept on in-feed or in-water medication. APP can be resistant towards antimicrobial substances, so that susceptibility testing should be performed in isolates from diseased pigs.Swine pleuropneumonia is traditionally controlled through antibiotic treatment. However, antibiotic resistance against widely used drugs like β-lactams and tetracyclines has emerged. This is particularly dramatic for those antibiotics that may be added to the water or feed.

  GAPS :

  The development of resistance is of major concern using antibiotics and should further be investigated in APP, especially macrolides as the resistance mechanisms are not clear. Regular surveillance for antimicrobial resistance determinants is essential.

  There is need for drugs, not being antibiotics, that can be used orally or parenterally and strategically, in combination with vaccinations, cleaning-disinfection, good housing and biosecurity.

  The right timing of the administration of antibiotics for metaphylaxis should be evaluated to comply with principles of prudent use of antimicrobials.

  Within the herd variability of antimicrobial resistance and speed of resistance induction / selection and subsequent diagnostic protocol on the frequency rate of AMR profiling is needed to substantiate the prescription of specific higher order of AM-drugs.

  In many countries penicillin G, a highly effective and first choice antimicrobial for APP is not available as an orally administered product. The efficacy and safety of oral penicillin should be evaluated to increase prudency of its use for the treatment of APP. Regulatory barriers may need to be overcome to allow such use, in case it is efficacious.

  Research into the binding sites of the toxin has found that ApxIII binds to CD18 subunit of β2 integrin, while ApxI and II bound to very similar glycan structures. This research should be extended to find potential treatments to block the interaction of toxins with host cells or develop soluble glycans or structural compounds the same as the glycans to which the toxin binds instead of the host cell.

• Biosecurity measures effective as a preventive measure

  It is unlikely to keep out the APP if you have a pig replacement programme which will require a quarantine and isolation facility. Strict separation of age groups and no contact between different age groups looks promising as a vehicle to prevent transmission. All-in-all-out technology is highly effective to control (reduce) disease, but the biological mode of action of this phenomenon is unknownIf buying weaners for a finishing unit, there is always a possibility of infection/disease if there is too much stress in the system. In these circumstances the only suggestion is to buy from one source that is free from clinical disease and serologically negative.In general, the control of other respiratory pathogens may reduce the impact of APP. While PRRSV and PCV2 have not been proven to be trailblazers of Porcine pleuropneumonia the impact of mycoplasma is assessed as much higher. Vaccination for concurrent infections such as Mycoplasma hyopneumoniae might greatly reduce the damaged lung available for colonization by APP which is one of the last colonizers of the piglets respiratory tract: Colonization is considered to take place in piglets after 14 days of age usually. APP may very well colonize pigs early as well during exposure to sows, e.g. at 3 or 5 days old, in susceptible herds.Factors that explain early / late colonization are unknown, just as the sow factors that explain the level of shedding/transmission by individual sows. Relevance of maternal antibodies on clinical outcome are clear, but so far antibody titers could not explain the difference of transmission between sow and its offspring (Tobias et al. 2014b).Usually clinical cases are observed in growing and sometimes finishing animals (late growing, early finishing stage).

  GAPS :

  There is no agreement on how to establish a herd status regarding APP. A herd certification process should be further discussed. With the background of European trade exchange the aim of this discussion should be the establishment of breeding programmes mandatory free of APP according to an elaborated method of certification (which still have to be identified).

  There is need to establish measures at the region/country levels. If a known population of APP serotypes is co-circulating in a country/region, then passive and natural immunization is expected (or active using vaccines). Measures to avoid the entrance of “exotic” serotypes are essential.Control of swine influenza A viruses and association with APP lung lesions due to influenza virus should be further investigated.

  Measures at the herd level should also include monitoring to avoid new serotypes coming into, and other complementary actions to live in harmony with the infection without the disease.

  The relevance of maternal antibodies on piglet colonization should be quantified and which epitope should be effectively blocked to prevent colonization.

  Sow / piglet factors that explain difference of transmission among sows to their offspring should be identified.

• Border/trade/movement control sufficient for control

  Herds of origin can easily be tested by serology or PCR to evaluate the herd status, more important than individual status. Then animals can be retested in quarantine (this is done in a routine way in North America and probably other countries such as Denmark). Border trade is extremely important since some virulent serotypes are present in some countries and not in others (Export from SPF pigs tested free from APP. from Denmark and other countries). Trade between pig breeding companies may facilitate spread of different serotypes/strains to regions previously unknown to this serotype/strains.

  GAPS :

  There is need to develop systems to get key samples (in vivo), and tests with high sensitivity (e.g. tonsils + PCR) to detect carriers.

  Request a certificate of freedom from certain serotypes before moving animals. International legislation concerning APP status and trading live animals in Europe.

• Prevention tools

  Vaccination and conversion to SPF units are currently used and allowed. Strategic medication is still used, but considered as not using antimicrobials prudently and should only be done, if at all, in case of emergencies for a limited period of time.

  Optimal external biosecurity measures should be taken (knowledge of the disease status of the incoming animals; quarantine in an isolated facility for at least 42 days).

  There are reports that APP can be eradicated without total depopulation under specific biosecurity conditions, but there is considerable publication bias on this subject. Only successful eradication efforts are published, but many more attempts have been made and not published. In general, odds of success for eradication of APP from sow farms are considered very low without depopulation. From finishing farms odds may be higher, using very strict biosecurity measures.

  GAPS :

  The effect of vaccines has so far not been very impressive with respect to infection, colonization and transmission of the agent.

  Protocols of eradication should be evaluated (also for cost-effectiveness).

• Surveillance

  Surveillance for APP is extremely important and done on a routine base for breeding companies.

  GAPS :

  Development and implementation of surveillance systems to detect new serotypes or variants of APP in regions or country may be desirable, especially for those strains with increased virulence or being resistant to specific antimicrobial substances (regular surveillance for antimicrobial resistance).

  Untypable strains should be submitted to a reference laboratory for further characterization to be aware of new strains arising. Whole genome sequencing is useful not only for determining the serotype of ‘untypable’ isolates, but also for the identification of antimicrobial resistance genes.

  Serological surveillance for newly purchased animals for strains which are not circulating in specific geographic region.

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

  All methods of control depend on correct diagnosis, identification of serotypes causing the problem, and use of commercial or autogenous vaccines or use of antibiotics to which the cultured organisms are sensitive.The eradication is stated in some cases but highly depends on the herd and the methodology, failure occurs in most cases, so that eradication seems to be not feasible at present. The only way to get rid of the disease at the moment is replacing all animals with new animals free of APP (depop-repop).

  GAPS :

  With available vaccines eradication is not possible. Further research for new effective vaccines is necessary.

  The impact of environmental and/or climate corrections on control of pleuropneumonia should be assessed and especially better scientific evidence is needed to define what good / optimal climatic conditions are, given all innovations on housing types for pigs in recent years.

  Eradication programs should be further elaborated and documented.

  There is a need for a realistic system focused on the control of the disease in terms of economics, applying prudent use of antibiotics, improving housing standards, and calculating profitability at the end of the rearing, as well as the finishing period.

  There is a need for strain characterization methods more than serotyping which will be helpful for future control strategies according to vaccine development and differentiation between virulent and non-virulent strains.

• Costs of above measures

  Not much reliable data is available. All measures are expensive in terms of quarantine, treatment and vaccination. If not successful then mortality, morbidity, culling, depreciated carcasses and veterinary costs as well as loss of production are very large.

  GAPS :

  Need to generate economic data under different rearing systems and the influence of secondary pathogens and disease pattern on farm. In parallel, indicators for the variation of costs should be elaborated.

  Opportunity costs such as growth deprivation etc are not well known for pleuropneumonia and they need to be objectively and systematically calculated.

• Disease information from the WOAH

• Disease notifiable to the WOAH

  Not reportable.

• WOAH disease card available

  N.A.

• WOAH Terrestrial Animal Health Code

  N.A.

• WOAH Terrestrial Manual

  N.A.

• Socio-economic impact

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

  Unlikely to be any.

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

  Unlikely to be any.

• Direct impact (a) on production

  APP can have a considerable effect on production, because mortality and morbidity can increase dramatically, until the stressing agents and concurrent diseases are removed.Cranioventral pulmonary consolidation and pleurisy in slaughter pigs have an impact on losses, carcass and meat quality (Maes et al. 2023).The consequence of disease related to APP can be an extended fattening period, decreased body mass gain and decreased feed conversion, which contribute to financial losses caused by the disease.

  GAPS :

  Need for data on opportunity costs from the field.

  Need for assessment of the high impact on animal welfare.

  Need for automation of measuring lung and pleurisy lesions of fattening pigs in the slaughterhouse, and further processing of the obtained data (e.g. via AI tools) as routine feedback data for the farmer.

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

  Public measures are unlikely to be affected but the costs of culling, carcase disposal, morbidity, mortality, medicines and possibly vaccination for several diseases can be very expensive. These may even necessitate partial or total depopulation with full cleaning and disinfection, drying, a rest period and repopulation with clean stock. High cost for breeding companies if becoming positive. Within infected and diseased herds problems will become less severe, when herd immunity to the strain causing the problem is increased, or/and stress factors and concurrent agents/diseases are removed. These measures to be taken have high a economic impact.

  GAPS :

  Due to the antibiotic usage to prevent or cure the disease public health may be impaired due to selection of e.g. MRSA or ESBL in the environment.

• Indirect impact

  Subclinically infected breeding herds are much often involved in serious problems with APP. The relationship between farrowing-to-weaning farms and fattening pigs might be disturbed due to the occurrence of the disease.Apart from economic losses to farmers, treating APP infections increases antibiotic consumption, thereby the risk of developing antimicrobial resistance transferrable to humans in APP and other bacteria present.

  There is an economic effect for the abattoir, because of a potentially high occurrence of pleurisy, which requires batches of pigs affected to be dealt with separately as they often require pleural stripping and entry into the hospital accommodation prior to condemnation of ribs etc. This slows down the line. Thus, the abattoir may dictate to producers when their pigs are taken or may even refuse them. The exact effect of APP in pleurisy in pigs is still unknown. Nowadays, very often pleurisy is also reported in APP negative pigs.

  GAPS :

  There is little specific data on the tons of antibiotics that reach water and soil, so the extent of the problem is currently not known.

  The additional contribution of APP and other pathogens in the development of pleurisy in pigs is not quantified so far.

  The disease leads to drawback in sustainability assessment of the affected farm due to losses.

• Trade implications

• Impact on international trade/exports from the EU

  Freedom form APP infection is important when exporting breeding animals to countries within and outside EU, e.g. Russia.

  GAPS :

  Recommendations are lacking, which tests or test protocols should be used (exact test or combination thereof, on which number of animals and at which frequency, and what to do when incidental positive results return (could be false positive).

• Impact on EU intra-community trade

  Freedom from APP infection is important when exporting breeding animals and piglets.

• Impact on national trade

  Unlikely to be any.

  GAPS:

  Creation of a “APP-free” label after establishing a general recommendation for sampling sizes, sampling methods, diagnostic tests and the interpretation of results for routine surveillance.

• Links to climate

  Seasonal cycle linked to climate

  Not demonstrated so far.In the Netherlands an increased incidence of APP lesions in necropsied pigs, as well as suspicions by veterinarians recorded in online disease monitoring program is seen in the fall and winter.

  GAPS :

  Seasonality may affect climatic factors that can act as trigger to induce adverse clinical outcome in colonised pigs. However, sound scientific evidence on this matter is lacking.Empirically observed trigger factors are air draught, cold, high difference between minimal and maximum temperatures within a day.

• Distribution of disease or vector linked to climate

  Not demonstrated so far.

• Outbreaks linked to extreme weather

  Not so unless excessive chilling in slatted units. Draughts are also linked to adverse clinical outcomes.

  GAPS :

  Climate effects on disease ourbreaks should be investigated under standardized conditions. It could be a model for other diseases.

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

  In general, climate disorders predispose to any respiratory disease, including (pleuro-) pneumonia caused by APP.

• Main perceived obstacles for effective prevention and control

  Untypable strains and inconclusive typing results lead to difficulties in diagnostics.

  Whole genome sequencing is too expensive for routine diagnostic (strain typing).

  GAPS :

  Practicle impact of untypable strains and strains with inconclusive typing results not known.

  Vaccines are not always successful in improving outbreak recurrent situations in farms.

Global challenges

• Antimicrobial resistance (AMR)

• Mechanism of action

  For identification of antimicrobial resistance genes - with the exception of macrolides- whole genome sequencing data can be used to accurately predict resistance of APP to the tested antimicrobial agents and provides added value for routine surveillance (Bosse et al. 2017).

  GAPS :

  Further knowledge on whole genome sequencing data and analysis of antimicrobial resistance.

• Conditions that reduce need for antimicrobials

  Good housing conditions, regular cleaning, high level of hygiene, proper ventilation, not mixing animals, all-in-all-out system can reduce the risk of the disease.

  GAPS :

  Gaos in knowledge on natural resistance; surveillances of APP at national level

• Alternatives to antimicrobials

  Vaccines.

  GAPS :

  Improvement of vaccines.

• Impact of AMR on disease control

  In general terms, the antimicrobial sensitivity for APP is good for most of the antimicrobial tested using in vitro conditions (Hennig-Pauka et al. 2022). It is certain that most of the information is collected in Europe (Vilaró et al. 2023; de Jong et al. 2023).

  GAPS :

  Further research on APP control to avoid impact of AMR.

• Established links with AMR in humans

  A monitoring of the antimicrobial susceptibility of last-resource antimicrobials (quinolones, cephalosporins, polymyxins) for APP in Spain resulted in a stable or increasing antimicrobial susceptibility of APP (Vilaró et al. 2023).

  GAPS :

  Knowledge about AMR of APP is necessary to recognise any connections

• Digital health

• Precision technologies available/needed

  Technologies for recognising pig health partially available.

  GAPS :

  Technologies should be expanded and improved.

• Data requirements

  Data is not uniformly available.

  GAPS :

  Animal health data should be collected in a standardised manner (national and European databases).

• Data availability

  Data is only available to a limited extent (data protection).

  GAPS :

  Animal health data should be available to all in anonymised form while ensuring data protection.

• Data standardisation

  Data are not standardized

  GAPS :

  Animal health data should be collected in a standardised way so that it can be used uniformly.

• Climate change

• Role of disease control for climate adaptation

  Probably low, but control of APP leads to improved feed conversion rate and higher sustainability.

  GAPS :

  Should be analysed.

• Effect of disease (control) on resource use

  Presumably low savings in water and CO2 emissions, higher feed conversion rate in healthy animals, less losses.

  GAPS :

  Should be analysed.

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

  Disease control would bring less losses, less waste, better feed conversion rate, higher sustainability, minor improvements expected.

  GAPS :

  Should be analysed.

• Preparedness

• Syndromic surveillance

  It could be very useful to include this bacterium in syndromic surveillance at regional level. This approach has been explored for many pig diseases including APP in the literature. It could be used for addressing the distribution of some APP serotypes at regional level (Alba-Casals et al. 2020).

  GAPS :

  Should be analysed.

• Diagnostic platforms

  Missing.

  GAPS :

  Should be analysed.

• Mathematical modelling

  Missing.

  GAPS :

  Should be analysed.

• Intervention platforms

  Missing.

  GAPS :

  Should be analysed.

• Communication strategies

  Missing.

  GAPS :

  Should be analysed.

Main critical gaps

• • Immunity development after infection with different strains
  • Immunity development after vaccination with different vaccines containing different adjuvants
  • Impact of coinfecting agents on pathogenesis,disease and development of immunity

Conclusion

• This bacterium has probably received more attention than many other bacteria in veterinary medicine and this research has shown the complexity of bacterial pathogenesis and virulence factors without yet producing the totally effective diagnostic techniques and vaccines required. The disease has a high economic impact on breeders.The widespread use of antibiotics, sometimes indiscriminate, and the marketing of growth-promoting drugs in countries outside Europe mask the real problem. It is not enough to slow the mortality caused by the disease. It is important to take a step further and to reduce economic losses due to the decrease in weight gain and extra costs due to medication.

  It is foreseen that the clinical impact of APP will rise again, as the use of AM has been reduced extensively, as is already seen in some countries (e.g. NL).

  Extension of SPF production including freedom of APP should be supported.

  In the US the early weaning /multiple site system was partly successful to produce APP-free piglets. This system should be evaluated also for other countries.

Sources of information

• Expert group composition

  Expert opinions and literature cited in the text.

  Isabel Hennig-Pauka, University of Veterinary Medicine Hannover, Germany- [Leader]

  Giovanni Loris Alborali, Istituto Zooprofilattico Sperimentale della Lombardia e dell’Emilia Romagna, Italy

  Branko Angielovski, Cyril and Methodius University Skopje, North Macedonia

  Christelle Fablet, French Agency for food safety (ANSES), France

  Lazlo Fodor, University of Veterinary Medicine, Budapest, Hungary

  Lorenzo Jose Fraile Sauce, University of Lleida, Lleida, Spain

  Marcello Gottschalk, University of Montreal, Canada

  Paul Langford, Imperial College London and The Royal Veterinary College, London, UK

  Dominiek Maes, Ghent University, Belgium

  Enric Marco, Marco Vetgrup, Spain

  Katrin Strutzberg-Minder, IVD Innovative Veterinary Diagnostic Gmbh, Germany

  Tijs Tobias, Utrecht University and Royal GD, the Netherlands

  Conny Turni, The University of Queensland, Australia.

• Date of submission by expert group

  July 2024

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