Diseases

Avian chlamydiosis (C. psittaci)

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Control Tools

  • Diagnostics availability

  • Commercial diagnostic kits available worldwide

    • Few commercial tests exist for the detection of antibodies by ELISA.. None of these antibody detection assays are C.psittaci specific.
    • Few commercial antigen detection tests are available, based on immunofluorescence detection or the use of antibodies for ELISA or immunohistochemistry (antibodies from several commercial companies). These tests can be used for the detection of C.psittaci antigens in animal samples but none of these antigen detection tests are C.psittaci-specific.
    • Few commercial PCR tests are available for the detection of C.psittaci DNA in animal and/or human (zoonosis) samples.
    • In humans the optimal sample type is currently deep respiratory secretions. This is often not available. Additional sample types like faeces/urine/blood have not been well evaluated.

    List of commercially available diagnostics (Diagnostics for Animals)

    GAPS :

    • Chlamydia psittaci-specific antibody detection tests are lacking.
    • Chlamydia psittaci-specific rapid molecular and/or antigen-based assays are lacking.

  • Diagnostic kits validated by International, European or National Standards

    GAPS :

    • Test comparisons of diagnostic kits have been reported in the literature, but large scale inter-laboratory comparisons are required to properly validate these tests. Part of the problem is the lack of available known and validated positive and negative avian samples.
    • Some of the commercial antibody detection test kits claim to be specific for detecting C.psittaci, when they are known to cross react with other chlamydial species, thus causing issues with regard to the detection of true positives.

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

    Avian chlamydiosis is mentioned in Chapter 10.1 of the WOAH Terrestrial Animal Health Code of 2023; woah.org. Regarding standards for diagnostic tests for avian chlamydiosis, the text refers to the general WOAH Manual of Diagnostic Tests and Vaccines for Terrestrial Animals.

    1. Identification of the target

    1. Cytological stainings or immunofluorescence stainings of impression smears of tissues and/or smears of exudates or faeces.
    2. Antigen detection ELISAs
    3. Conventional PCR and real time PCR of pharyngeal, ocular or faecal swab samples and/or tissues/organs
    4. Isolation of C.psittaci in embryonated chicken eggs or in tissue culture.
    5. But the latter is not for routine diagnosis, but more for retrospective examination of samples for chlamydiae.

    2. Serology

    The main serological methods that are being used for detecting chlamydial antibodies are: (1) various methods of elementary body agglutination (EBA); (2) the complement fixation test (CFT); 3) indirect (micro) immunofluorescence (MIF) tests; 4) commercial ELISAs; and 5) immunoassay-based lateral flow tests.

    GAPS :

    • Standards, specifically for diagnosis of avian chlamydiosis should be included in WOAH documents and/or European Standards (EU).
    • The EBA and CFT should be replaced as the internationally recognised diagnostic standard with a more sensitive and specific serological test.
    • Need for rapid, sensitive and specific point of care (PoC) tests.
    • Need better agreement and standardisation between National Reference and other testing laboratories on the procedures and methodologies used for the routine diagnosis of C.psittaci.

  • Commercial potential for diagnostic kits in Europe

    As C.psittaci is endemic in Europe and throughout the world, the potential for commercial development of kits is clear.

  • DIVA tests required and/or available

    There is no commercial C.psittaci vaccine. DIVA tests are required once commercial vaccines are available as:

    • None of the existing serological tests would be able to differentiate C.psittaci antibodies resulting from a natural infection and those induced by vaccination.
    • Molecular methods (PCR and qPCR) are needed for differential detection of a future vaccine and natural wild-type isolates.

    GAPS :

    • Serological tests for C.psittaci to detect a natural infection in vaccinated poultry flocks and pet birds should be developed (DIVA tests), validated through inter laboratory trials and commercialised.
    • A molecular DIVA test should be validated in inter-laboratory trials and commercialised.

  • Vaccines availability

  • Commercial vaccines availability (globally)

    There is no commercial C.psittaci vaccine but research is ongoing.

    GAPS :

    • Investigate different approaches to developing a novel efficacious vaccine, including the development of a DIVA-compatible vaccine.
    • Identification of protective vaccine candidate antigens is needed.
    • Bird species specific immunological toolboxes (i.e. leukocyte markers) are required for in depth analysis of the immune response following natural infection and/or immunization.
    • One of the problems in C.psittaci vaccine development is also that BSL3 and A3 (animal facilities) are needed as the agent spreads through aerosols from birds to humans, causing psittacosis in humans. C.psittaci is also classified as bioterrorism agent/disease category B (https://emergency.cdc.gov/agent/agentlist-category.asp ).

  • Marker vaccines available worldwide

    No marker vaccine for C.psittaci.

    GAPS :

    DIVA vaccines are required.

  • Effectiveness of vaccines / Main shortcomings of current vaccines

    Not applicable as no commercial vaccines available.

    GAPS :

    DIVA vaccines are required.

  • Commercial potential for vaccines in Europe

    • High, particularly in those countries with endemic problems and high density of susceptible species of poultry, (exotic) wild birds and companion birds.
    • Beneficial for trade/importation of birds.

  • Regulatory and/or policy challenges to approval

    From the perspective of biosafety, C.psittaci trials require BSL3 and A3 facilities.

    GAPS :

    • Implementation of C.psittaci in routine diagnosis in poultry.
    • In analogy with the policy change on diagnosis of human C.psittaci infections in The Netherlands, where the impact of C.psittaci on public health became clear when C.psittaci was included in the routine diagnostic PCR panel for community acquired pneumoniae (CAP).
    • Studies on the economic impact of C.psittaci infections in poultry are needed, as prevalence differs between poultry species and countries.
    • Awareness of the economic impact of the infection for poultry would increase the demand for a vaccine and could lead to obligatory vaccination of industrial poultry.
    • Obligatory vaccination of avian risk populations, such as parakeets, parrots, cockatiels and lorries (Psittacidae) and perhaps of pigeons would lead to higher interest from pharmaceutical companies for this niche market.
    • Veterinary vaccination/health certificate for trade/import of avian risk populations, birds sold in pet shops or present at bird exhibitions.

  • Commercial feasibility (e.g manufacturing)

    Depends on the vaccine type.

    GAPS :

    Assess different vaccine development strategies for their ease of manufacture and industrialisation.

  • Opportunity for barrier protection

    Vaccines:

    • Future use as part of a poultry flock control programme and zoonosis prevention in European countries.
    • Future use as part of a control and zoonosis prevention programme in Psittacidae in European countries.
    • Future use as part of a control and zoonosis prevention programme in pigeons in European countries.

  • Pharmaceutical availability

  • Current therapy (curative and preventive)

    • Tetracyclines are the drugs of choice for treating avian chlamydiosis (medicated feed for 14 to 45 days or injection for individual birds, using 8 to 10 injections in a 45-day period, for instance in psittacine pet birds).
    • In humans, severe CAP including severe C.psittaci pneumonia is often emperically treated with (third generation) quinolones. Targeted therapy -if diagnosed with C.psittaci - with doxycycline or macrolides like azithromycin.

    GAPS :

    • Nevertheless, treatment is often not capable to eliminate psittaci fully, especially in immuno-compromised birds.
    • Routine antimicrobial resistancy testing or surveillance is lacking.

  • Future therapy

    GAPS :

    Development of natural biocides, bacteriophages, natural antimicrobials and innovative synthetic anti-microbials as therapeutics.

  • Commercial potential for pharmaceuticals in Europe

    If C.psittaci vaccines and diagnostic monitoring schemes are developed, then there should not be a major demand for new pharmaceuticals.

  • Regulatory and/or policy challenges to approval

    The requirement for BSL3 and A3 for growing C. psittaci will need to be discussed with manufacturing companies.

  • Commercial feasibility (e.g manufacturing)

    Feasible with the current knowledge on the biology of chlamydia infections. However, for some innovative anti-microbials, the drug price might be an issue.

  • New developments for diagnostic tests

  • Requirements for diagnostics development

    • Validation of recently developed tests to identify latently infected animals and distinguish vaccinated from naturally infected animal (DIVA).
    • Comparison and evaluation of existing diagnostic tests on a pan-European scale.
    • Serological tests: development of host species-specific antibody detection tests.

    GAPS :

    • DIVA tests should be applicable for poultry, pet birds and pigeons (vaccine target populations).
    • Requirement for safe and proper validated control samples (inactivated bacteria, bacterial DNA, recombinant bacterial proteins) in order to assess diagnostic tests and determine cut-offs for positivity.
    • Requirement for proper validated control sera in order to assess diagnostic tests and determine cut-offs for positivity.

  • Time to develop new or improved diagnostics

    Estimation: 4-5 years (test design, laboratory testing of sensitivity and specificity, inter-laboratory testing of standards, laboratory testing of field samples, inter-laboratory testing of field samples).

  • Cost of developing new or improved diagnostics and their validation

    Depends on the type of test.

  • Research requirements for new or improved diagnostics

    • Serological tests: Development of host species-specific serological tests for C.psittaci in different avian species.
    • Research towards rapid, sensitive and specific point-of-care tests.
    • In humans there is a need -especially during outbreaks and population studies- for specific a C.psittaci serologic test to prove recent exposure.

    GAPS :

    • Research towards direct identification of C.psittaci genomes in clinical samples.
    • Validation and comparison and field studies for future point-of-care tests.

  • New developments for vaccines

  • Requirements for vaccines development / main characteristics for improved vaccines

    There is a requirement for a safe, stable and cheap vaccine. The vaccine will likely be based on recombinant protein technology, as multi-component subunit vaccines, viral vectored vaccines, DNA or mRNA vaccines.

    GAPS :

    Although various virulence associated antigens have been described further research is needed to obtain a better understanding of protective immune responses, mucosal immunology and of the molecular mechanisms involved in infection. This may offer new perspectives for development of novel vaccine strategies as well as for diagnosis.

  • Time to develop new or improved vaccines

    5 to 10 years depending on the type of vaccine and the target species.

    GAPS :

    • The big question is what do the Pharmaceutical companies want in their next generation products, taking into consideration what is actually feasible from a scientific perspective? Discussions are ongoing between some scientific experts and the companies on this issue.
    • Consideration will need to be given to the fact that BSL3 and A3 facilities are needed as C.psittaci is classified as a risk level 3 pathogen.

  • Cost of developing new or improved vaccines and their validation

    Difficult to quantify but costs comparable to those for C. abortus vaccine development, but perhaps even more as BSL3 and A3 are required.

  • Research requirements for new or improved vaccines

    GAPS :

    • Development of new approaches to vaccine development.
    • Development of mucosal vaccines (poultry) and/or vaccines for mass application (poultry)
    • Novel (mucosal) adjuvants for birds.

  • New developments for pharmaceuticals

  • Requirements for pharmaceuticals development

    Data could be extrapolated to other obligate or facultative obligate intracellular bacteria.

  • Time to develop new or improved pharmaceuticals

    Time to develop would depend on the product and the trials necessary to validate efficacy and safety. Commercial production would then take further time. Five to 10 years is a realistic timeframe.

  • Cost of developing new or improved pharmaceuticals and their validation

    Expensive but difficult to assess as it will depend on the product and the trials necessary to validate and licence.

  • Research requirements for new or improved pharmaceuticals

    • Standardized in vitro
    • Standardized in vivo experimental infection models.

    GAPS :

    Additional in vitro models (preferably 3D, organoids).

Disease details

  • Description and characteristics

  • Pathogen

    • Chlamydia psittaci (formerly Chlamydophila psittaci) is an obligate intracellular Gram-negative bacterium belonging to the family Chlamydiaceae.
    • C.psittaci is currently divided into 15 outer membrane protein A (ompA) genotypes: A–F, E/B, WC, M56, 1V, 6N, Mat116, R54, YP54 and CPX0308. For genotypes A–F and E/B, a specific host predilection has been identified.

    GAPS :

    • We need more information on the contemporary genomes of novel C.psittaci genotypes.
    • It would be interesting to sequence the genomes of C.psittaci strains involved in zoonotic transfer, thus sequencing both the animal and transferred human isolates.
    • We need more information on virulence factors and the molecular pathogenesis of C.psittaci. Lot of genomes are from 90s, only recently there were 20 or so more contemporary. We need additional genomes.

  • Variability of the disease

    • Real-time PCR genotyping, and if enough C.psittaci DNA is available, ompA and MLST genotyping should be applied but whole genome sequencing is best.
    • Pathogenicity between genotypes might vary. For instance, genotype A and D were more virulent for SPF chickens and SPF turkeys than genotype B.
    • Real-time PCR genotyping, and if enough C.psittaci DNA is available, MLST can assist in tracing the human infection source. Humans can potentially be infected by any C.psittaci genotype, but some genotypes (e.g. genotype A) seem to be associated with a higher incidence of serious illness in patients than others. Reports on hospitalized psittacosis patients are predominantly related to zoonotic transfer of genotype A from infected Psittaciformes (cockatoos, parrots, parakeets and lories). Genotype B, frequently occurring in pigeons, is also often detected in psittacosis patients. Other genotypes reported to cause severe illness in humans are genotypes C and E/B, which frequently occur in poultry.
    • Livestock and other animals can potentially be infected by any C.psittaci, but some genotypes (e.g. genotype A/ ST24) seem to be associated with certain clinical manifestations. In Australia, reports of foetal loss in horses are strongly associated with spillover of genotype A/ ST24 from infected Psittaciformes (cockatoos, parrots, parakeets and lories). Other genotypes may cause a range of infections, from asymptomatic to more severe respiratory disease, reported in cattle.
    • A number of avian strains, previously referred to as C. abortus-C.psittaci intermediate strains, have recently been suggested to be close evolutionary ancestors of C. abortus. These strains are proposed to be classified as a new avian C. abortus subspecies and that they may represent a missing link in the divergence of C.psittaci into C. abortus.

    GAPS :

    • It would be interesting to sequence the genomes of C.psittaci strains involved in zoonotic transfer, thus sequencing both the animal and transferred human isolates. Based on latest genomics, these are ompA found in novel avian C. abortus (personal communication M. Jelocnik, 2023)
    • More information is needed on host-bacterium interactions for the different genotypes which have been identified so far. Why do certain genotypes preferably infect a specific bird species?
    • There are still gaps in our knowledge of the molecular pathogenesis of the infection. This is largely because genetic transformation of C.psittaci is still not successful. However, the latter might perhaps become feasible using recent knowledge on Chlamydia trachomatis transformation techniques.
    • We need to broaden our knowledge on mucosal immunology and host immunogenetics and their role in disease and protection.
    • Determine the pathogenic potential of the newly classified avian C. abortus strains in ruminant species.
    • Determine the zoonotic potential of these avian C. abortus strains and estimate the chance of underdiagnosis as not all tests detect this pathogen.

  • Stability of the agent/pathogen in the environment

    Chlamydia is reported to be relatively stable in the environment and can survive for long periods (weeks to months) in freezing temperatures and at normal temperatures for up to 30 days in faeces and bedding.C.psittaci bioaerosol monitoring technique has been established by researchers but is not routinely used.

    GAPS :

    This requires further investigation due to limited published data, and the importance of this question with regard to risks for transmission.

    • Need to investigate the viability of C.psittaci (survival and stability) in potential transmission vehicles (bedding, drinking water, pasture, soil, etc), as well as under different climatic conditions (temperature, humidity).
    • Need for optimization and validation of cleaning and disinfection methods for prevention of psittaci infections in the poultry industry (biosecurity).
    • Implementation of bioaerosol monitoring for C.psittaci in poultry barns, hatcheries, (psittacine) bird quarantine stations and other high-risk facilities.

  • Species involved

  • Animal infected/carrier/disease

    • Birds are the natural host, but C.psittaci might also infect mammals (ruminants, pigs, horses, guinea pigs, rodents hares…).
    • C.psittaci causes respiratory disease in birds. The infection might become systemic and lead to mortality.
    • Birds can remain persistently infected and be carriers of the organism for long periods but without showing clinical disease. A persistent infection is characterized by the presence of intracellular aberrant chlamydia bodies which no longer replicate and are larger than the metabolically active, replicating reticulate bodies. Nevertheless, aberrant bodies can revert to reticulate, replicating bodies.

    GAPS :

    • What is the role of wildlife (foxes, rabbits, rodents, etc) and birds (carrion, game, migratory, etc) as carriers and/or reservoirs of C.psittaci?
    • Investigate and compare host susceptibility and its determining factors for psittaci infection: poultry (respiratory disease) vs psittacine birds (respiratory disease), pigeons (respiratory disease), and ruminants (bronchopneumonia and/or milk drop syndrome).
    • Require further investigations to determine the anatomical site of latency or persistence in ruminants and birds.

  • Human infected/disease

    • During the COVID-19 pandemic and during the past years in general, more cases of respiratory illness due to C.psittaci have been reported. This is due to increased awareness, more testing and reporting.

    C. psittaci or psittacosis in humans

    • People at risk are pet bird owners, especially psittacine bird lovers and persons occupationally exposed to birds, like poultry workers (farmers, slaughterhouse employees and workers in poultry processing plants), laboratory workers, zoo workers, veterinarians, workers at customhouse offices or workers at avian quarantine stations as well as taxidermists. In addition, people visiting a bird exhibition or bird parks can also become infected as well as persons in contact (feeding) with urban pigeon colonies, ornithologists (wild bird droppings), wildlife rehabilitators and persons cleaning wild birds.
    • Humans can potentially be infected by any C.psittaci genotype, but some genotypes (e.g. genotype A) seem to be associated with a higher incidence of serious illness in patients than others. Reports on hospitalized psittacosis patients are predominantly related to zoonotic transfer of genotype A from infected Psittaciformes (cockatoos, parrots, parakeets and lories). Genotype B, frequently occurring in pigeons, is also often detected in psittacosis patients. Other genotypes reported to cause severe illness in humans are genotypes C and E/B, which frequently occur in poultry. Nevertheless, any bird species might be considered as a reservoir.
    • Psittacosis can result in an asymptomatic infection, or an acute symptomatic infection characterized by mild flu-like illness to severe atypical pneumonia and fulminant sepsis, which can be lethal in untreated patients.

  • Vector cyclical/non-cyclical

    Historically, the role of ticks as vectors for transmission of C. psittaci is considered to be negligible compared to especially aerogenic, oral, vertical and horizontal transmission in birds.

    GAPS :

    Taken current climate change into account, monitor whether vectors such as ticks, mites or fleas are more frequently involved as vectors (mechanical or otherwise) for transmitting infection.

  • Reservoir (animal, environment)

    • Asymptomatic carrier animals infected with C.psittaci are an important reservoir of infection.
    • Birds can remain persistently infected and in cases of stress, co-infections and or inadequate management procedures (e.g. ventilation in barns) can re-initiate shedding whereafter naïve animals can become infected.
    • psittaci can persist in the environment for days to months, depending on weather conditions (temperature and humidity).
    • Transmission of psittaci may occur between wild birds (mammals) and domestic birds (mammals) through direct contact, respiratory exudate or faecal droppings. Feed should be protected from wild birds.

    GAPS :

    • Determine the site of persistence of C.psittaci in asymptomatic carrier birds (body/tissues site).
    • Develop new bioaerosol sampling techniques.
    • Find out how far the organism can spread through the air in the vicinity of poultry farms and/or poultry slaughterhouses and what influences the aerogenic spread.
    • Determine if and how long C.psittaci can survive in environmental waters.
    • Examine the presence and genotype of C.psittaci in migratory birds.

  • Description of infection & disease in natural hosts

  • Transmissibility

    • C.psittaci is excreted in faeces and nasal discharges. Faecal shedding occurs intermittently and can be activated through stress caused by nutritional deficiencies, prolonged transport, overcrowding, chilling, breeding, egg laying, treatment or handling. Bacterial excretion periods during natural infection can vary depending on virulence of the strain, infection dose and host immune status.
    • The primary route of infection is by inhalation of respiratory exudate, contaminated dust from feathers and/or faecal material but transmission can also occur through ingestion of contaminated faeces. Blood-sucking ectoparasites, which include arachnids, lice and simulid flies, have been shown to transmit chlamydiae in turkeys but probably act as mechanical vectors rather than biological vectors.
    • Vertical and horizontal transmission has been demonstrated in birds.
    • C.psittaci penetrates chicken eggshells.
    • Avian species, including domestic poultry sharing aquatic or moist soil habitats with wild infected aquatic birds may become infected via contaminated water.
    • Granivorous birds like pigeons, doves, pheasants and house sparrows may become infected by dust inhalation in faeces contaminated barnyards and grain storage sites. The consumption of infected carcasses may transmit C.psittaci to host species that are predators or scavengers of other birds.
    • Transmission of C.psittaci in the nest is possible. In many species, such as Columbiformes, cormorants, egrets, and herons, transmission from parent to young may occur through feeding, by regurgitation, while contamination of the nesting site with infective exudates or faeces may be important in other species, such as snow geese, gulls and shorebirds.

    GAPS :

    Study the influence of genotypes on the transmissibility.

  • Pathogenic life cycle stages

    • C.psittaci, like other chlamydial species, undergoes a developmental cycle involving two developmental forms, the extracellular metabolically inactive infectious form (elementary body or EB) and the intracellular metabolically active form (reticulate body or RB). Both forms play an important role in the pathogenesis of the organism. The EB attaches to the host cell, enters and differentiates to the RB within a chlamydial inclusion. The RB multiplies within this inclusion, which fills most of the cells extranuclear space. At the end of the cycle the RBs re-differentiate back into EBs and the cell is lysed releasing the infectious organisms, which go on to infect neighbouring cells and thus causing the tissue damage that is characteristic of this disease.
    • The pathogenesis was well studied in experimentally infected SPF turkeys. In turkeys infected by aerosol, the primary site of replication is the upper respiratory tract where epithelial cells become infected. Subsequently, epithelial cells of the lower respiratory tract and macrophages throughout the respiratory tract become infected. Then, intense replication occurs in the respiratory tract. At the same time, chlamydiae can be demonstrated in plasma and monocytes, indicating septicaemia of various tissues throughout the body. The digestive tract, several parenchymatous organs, the pericardium, the bone marrow and the conjunctivae become infected and faecal shedding of the organism occurs as demonstrated by isolation of the agent from cloaca1 swabs. Production of large amounts of chlamydiae at the respiratory tract surface suggests also an aerogenic spread of the organism.

    GAPS :

    • Determine the role of the aberrant bodies in chlamydial persistence using in vivo models?
    • What is the site of persistence in asymptomatic animals?
    • What is the trigger for release of the organism from a persistent state to a replicating state?
    • Study the role of antibiotics (e.g. too low a dose) in inducing a persistent state.

  • Signs/Morbidity

    • Depending on the chlamydial strain and the avian host, chlamydiae cause pericarditis, air sacculitis, pneumonia, lateral nasal adenitis, peritonitis, hepatitis, and splenitis. Generalized infections result in fever, anorexia, lethargy, diarrhoea, and occasionally shock and death.
    • Acute infections in psittacine birds often lead to high mortality rates. Chlamydiosis is also a very common chronic infection of psittacine birds. Infections cause conjunctivitis, enteritis, air sacculitis, pneumonitis, and hepatosplenomegaly. Droppings are often green to yellow-green. Many of the birds become chronically infected, but show no clinical signs until stressed. These birds often shed chlamydiae intermittently and serve as a source of infection of humans and other birds.
    • Chlamydiosis is also a common chronic infection of pigeons. Clinical signs include conjunctivitis, blepharitis, and rhinitis. Mortality rates are usually less than 5%. Survivors can become asymptomatic carriers.
    • Infected turkeys show vasculitis, pericarditis, pneumonitis, air sacculitis, and hepatosplenomegaly, and lateral nasal adenitis at necropsy. Mortality rates of 5–40% may occur unless early antibiotic treatment is introduced.
    • Infected ducks show trembling, conjunctivitis, rhinitis, and diarrhoea. Mortality ranges to up to 30% unless early antibiotic treatment is introduced.

    GAPS :

    What is the role of chronic/subclinical C.psittaci infections in cases of bronchopneumonia or milk drop syndrome in ruminants?

  • Incubation period

    Depends on the virulence of the strain, the infective dose and the immune status of the host. Generally clinical signs appear within one week after exposure.

    GAPS :

    • What is the situation in non-avian species? This is currently unknown and should be investigated.
    • The localization of the pathogen (body/tissues site) during the incubation period in non-avian species should be investigated.

  • Mortality

    • Depends on the virulence of the strain, the infective dose and the immune status of the host.
    • Genotypes A and D are considered to be more pathogenic than genotype B and cause higher mortality rates as demonstrated experimentally in SPF turkeys and SPF chickens.

  • Shedding kinetic patterns

    • psittaci is excreted in large numbers in nasal (respiratory exudate) and/or ocular discharge and large numbers are also (intermittently) excreted in the faeces of birds.
    • The organism has also been found in ruminant milk (milk drop syndrome in cattle), but it is unclear as to the significance of this in terms of spread of infection.

    GAPS :

    The role of the GI tract as a potential reservoir for respiratory re-infection in birds or non-avian species should be investigated (analogous to C. trachomatis rectal infection in humans as a source of genital re-infection).

  • Mechanism of pathogenicity

    • Several in vitro models and animal models have been used to study the pathogenesis and pathogenicity of C.psittaci.
    • The destruction of respiratory epithelial cells, followed by septicaemia and replication (cell lysis) in all parenchymatous tissues of the bird.
    • Organ failure.
    • Severe inflammatory reactions following tissue damage.
    • C.psittaci replicates in and destroys macrophages, which are members of the innate immune system, the first line of defence in animals and humans. It renders the animals more vulnerable to other infectious agents. Co-infections with other bacteria and even viruses thus often occur.

    GAPS :

    • What differences are there in (molecular) mechanisms of pathogenicity for different genotypes in birds (respiratory disease)?
    • What differences are there in mechanisms of pathogenicity for different genotypes in non-avian species (ruminants, horses, etc)
    • What is the role of different bacterial secretion systems in virulence?
    • What is the pathogenic interplay with other (emerging) pathogens?

  • Zoonotic potential

  • Reported incidence in humans

    C.psittaci in humans = psittacosis

    • Mandatory notifiable disease in many countries.
    • In Belgium, the number of reported positive laboratory results clearly increased since 2010, and in 2017, the number almost doubled (n = 44) compared to the two previous years. In 2022, 37 cases were reported. The number of psittacosis cases in Belgium, as in other countries, is probably highly underestimated, because of underdiagnoses and underreporting.
    • In the Netherlands, about 40 to 90 human psittacosis cases are reported yearly. However, according to a study in The Netherlands, more than 1500 symptomatic psittacosis patients remained undiagnosed yearly between 2012-2014. The study used the methodology developed for the Burden of communicable diseases in Europe toolkit of the European Centre for Disease Prevention and Control (ECDC).

    GAPS :

    • Implementation of C.psittaci molecular diagnosis (PCR) and if not already in place, reimbursement of the tests by the health insurance.
    • Thus, National health authorities should provide legal and financial support to implement C.psittaci PCR and molecular characterization, at least in hospitalized patients with CAP. In addition, a one health approach, meaning a close collaboration between human and animal health agencies, medical and veterinary diagnostic laboratories, hospitals and medical and veterinary practitioners is needed for C.psittaci surveillance, prompt notification and correct treatment of both the infection source (or implementation of appropriate infection prevention measures) and the patients.

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

    Psittacosis has been observed throughout the world. The disease occurs sporadically or in outbreaks, related to pet shops, pet birds, bird parks, feeding urban pigeons, bird exhibitions, ornithologists, wild live rehabilitators, persons cleaning wild bird feeders, veterinary facilities, bird quarantine stations, poultry flocks and poultry slaughterhouses.

    GAPS :

    • Strict implementation of preventive measures in risk populations
    • Stricter (diagnostic) regulations on national and international bird trade.
    • Recording transactions, and testing of birds for C.psittaci before trading/selling them in shops.
    • Diagnostic monitoring in birds frequently in contact with the public.
    • Wearing gloves, protective clothing, a mouth-nose mask (preferably FFP3) and eyewear to prevent rare cases of keratoconjunctivitis, or a full-face mask during contact with possibly infected birds.
    • If a bird is to be kept as a pet, it is advisable to have it tested by a veterinarian for C.psittaci infection or carriage when the bird trader has not yet done so.
    • Risk assessment and management of C.psittaci in poultry processing plants in order to prevent occupational disease.

  • Symptoms described in humans

    Psittacosis can result in an asymptomatic infection or an acute symptomatic infection characterized by mild flu-like illness to severe pneumonia and fulminant sepsis, which can be lethal in untreated patients. The incubation period varies from 5 to 14 days, but historically, based on serological diagnosis, longer periods have been noticed depending on the infection dose, the virulence of the C.psittaci strain and the susceptibility of the patient.

    GAPS :

    Investigate more cases of respiratory infections in humans and any association with exposure to C.psittaci.

  • Likelihood of spread in humans

    Human-to-human transmission occurs with C.psittaci, but it is considered to be rare.

    GAPS :

    Investigate infection and disease in endangered avian species that are subject to ex-situ breeding programmes in captivity.

  • Impact on animal welfare and biodiversity

  • Both disease and prevention/control measures related

    Longterm antibiotic treatment of asymptomatic birds involved in human psittacosis cases can lead to antibiotic related adverse events and potential antibiotic resistance development while antibiotic treatment is not needed for these birds themselves.

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

    To our knowledge unknown.

  • Slaughter necessity according to EU rules or other regions

    A laboratory diagnosis of C.psittaci in birds is notifiable in many countries, as it is a zoonotic infection. Depending on the severity of the situation/country, appropriate, by law dictated, control measures will be implemented. Slaughter is a possibility.

  • Geographical distribution and spread

  • Current occurence/distribution

    • Chlamydial respiratory disease resulting from psittaci infection occurs in all poultry rearing countries worldwide.
    • C.psittaci infections in birds (pet birds, backyard birds, pigeons, wild birds, etc) are occurring worldwide.

    GAPS :

    C. psittaci should be implemented in screening/monitoring programmes for especially poultry and should be implemented in molecular diagnostic panels for CAP in humans.

  • Epizootic/endemic- if epidemic frequency of outbreaks

    Highly underestimated as not included in routine bacteriological diagnosis, probably historically because of its obligate intracellular nature.

    GAPS :

    • Chlamydia psittaci infection kinetics in broilers (chickens/turkeys) has been described but infection kinetics in other poultry broilers (i.e. ducks, geese) is still unknown.
    • Infection kinetics on breeder farms and in laying farms is unknown, regardless of the poultry species.
    • Infection kinetics in bronchopneumonia and milk drop syndrome in cattle are unknown and infection kinetics in other non-avian species is also unknown.

  • Speed of spatial spread during an outbreak

    Spread of infection can be rapid depending on the amount of infectious material in the environment and the maternal immunity status of the poultry flock.

    GAPS :

    What is the psittaci situation in non-avian species?

  • Transboundary potential of the disease

    As for avian influenza, role of wildlife (wild birds, i.e. duck species, Canada goose and other migratory birds) as carriers or reservoirs of C.psittaci infection is recognized.

  • Route of Transmission

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

    See also Section “Description of infection & disease in natural hosts/Transmissibility”.

    • C.psittaci is excreted in faeces and nasal discharges. Faecal shedding occurs intermittently and can be activated through stress caused by nutritional deficiencies, prolonged transport, overcrowding, chilling, breeding, egg laying, treatment or handling. Bacterial excretion periods during natural infection can vary depending on virulence of the strain, infection dose and host immune status.
    • The primary route of infection is by inhalation of respiratory exudate, contaminated dust from feathers and/or faecal material but transmission can also occur through ingestion of contaminated faeces. Blood-sucking ectoparasites, which include arachnids, lice and simulid flies, have been shown to transmit chlamydiae in turkeys but probably act as mechanical vectors rather than biological vectors.

    GAPS :

    Study the influence of genotypes on the transmissibility.

  • Occasional mode of transmission

    See Section “Description of infection & disease in natural hosts/Transmissibility”.

    • Avian species, including domestic poultry sharing aquatic or moist soil habitats with wild infected aquatic birds may become infected via contaminated water.
    • Granivorous birds like pigeons, doves, pheasants and house sparrows may become infected by dust inhalation in faeces contaminated barnyards and grain storage sites. The consumption of infected carcasses may transmit C.psittaci to host species that are predators or scavengers of other birds.
    • Transmission of C.psittaci in the nest is possible. In many species, such as Columbiformes, cormorants, egrets, and herons, transmission from parent to young may occur through feeding, by regurgitation, while contamination of the nesting site with infective exudates or faeces may be important in other species, such as snow geese, gulls and shorebirds.

  • Conditions that favour spread

    Poor management procedures (biosecurity, temperature, humidity and ventilation in barns, etc) in poultry farms.See Section “Description of infection & disease in natural host”.

    GAPS :

    • What is the effect of free ranging (interaction with wild birds/fowl) of poultry on the occurrence and spread of the infection?
    • What is the effect of new ‘poultry animal welfare’ housing systems (enriched cages or alternative housing for layers) on the occurrence and spread of the infection.
    • What is the effect of zero grazing (higher density of animals that are kept inside) on C.psittaci respiratory disease and milk drop syndrome in cattle?
    • See also 9. description of infection in natural host.

  • Detection and Immune response to infection

  • Mechanism of host response

    • Both innate, as a first line of defence, and adaptive immune responses are important in the control of chlamydial infections.
    • Both cellular and humoral immunity have been demonstrated, although cellular responses appear more important in terms of a primary infection.
    • The primary infectious dose appears to be an important factor that determines disease outcome.

    GAPS :

    Requirement to investigate mucosal immune responses.

  • Immunological basis of diagnosis

    • Antibody detection alone is not particularly useful in diagnosing a current chlamydial infection in birds because of the high prevalence of this infection in birds and the long-term (up to several months) persistence of anti-chlamydial antibodies. In most bird species, there is a high background rate of anti-chlamydial antibodies, and until we have more information on the disease pattern in certain bird species in relation to direct identification of the bacteria and serology, we are unable to comment on the real significance of antibody titres obtained. Thus, to determine if a single bird is infected, serology should always be used in conjunction with antigen or gene detection, or paired sera should be examined.
    • Antigen detection is in most countries replaced by specific DNA detection assays for C.psittaci.

    GAPS :

    • Immune mechanisms of persistent infections should be further investigated.
    • The majority of current commercial C.psittaci antibody detection tests are not specific and cannot distinguish C.psittaci from other Chlamydia species.

  • Main means of prevention, detection and control

  • Sanitary measures

    Effective biosafety and biosecurity measures.

    GAPS :

    • Vaccine development and implementation of vaccine strategies in the whole poultry production chain (breeders, boilers, layers) as vertical and horizontal transmission occurs.
    • Vaccine development and implementation for companion birds.

  • Mechanical and biological control

    When C.psittaci respiratory disease occurs, the use of long acting tetracyclines can be administered as an emergency treatment to improve the health of the animals and to reduce further potential losses but should not routinely be used as a means of controlling infection due to issues of potential antibiotic resistance.

    Attention must be paid to:

    • Removal and destruction of contaminated bedding by burning or incineration (also, all-in, all out principle).
    • Cleaning and disinfection procedures to prevent persistence and environmental contamination.
    • Operating basic standards of hygiene (e.g. hand washing) and obligatory use of personal protective equipment (clothing, boots, gloves) to prevent spread of infection.

  • Diagnostic tools

    A range of tools are available for diagnosing C.psittaci infection.

    There are advantages and disadvantages to the use of some of these tests. Serological antibody detection tests also detect antibodies induced by infection with other chlamydiae, including C. abortus (poultry and ruminants), C. gallinacea, (poultry, until now not associated with clinical disease and mortality in poultry) or C. avium (Psittacidae and pigeons) which can be present and can result in false positive test results and perhaps unnecessary treatment (for instance in case of C. gallinacea).Molecular detection of organism DNA is generally superior over serology, being more sensitive and specific, although requiring more specialist equipment and is generally more expensive.None of the current tests can detect persistently infected carriers.There are no DNA based diagnostic tests that can differentiate viable bacteria from DNA contaminated samples.

    GAPS :

    • Develop diagnostic tools that are able to detect persistently infected animals.
    • New antibody ELISAs (easy for testing multiple samples and monitoring; taking the DIVA principle into account) that are more sensitive and especially more specific need to be developed for poultry (chickens, turkeys, ducks, geese).
    • Development of point-of-care tests for diagnosing (individual) infections in the field for different poultry species and point-of-care tests for diagnosing infections in companion birds.
    • Develop and validate approved tests for certifying animals free of disease for export purposes (poultry, poultry products, pigeons, Psittaciformes).
    • Develop viability PCR’s for C.psittaci
    • Develop and evaluate tests for detection of C.psittaci infections in cattle.

  • Vaccines

    In general, vaccine design and development are an inherently laborious process.

    There are no commercial vaccines yet.

    In general, modern Chlamydia vaccine research should be focused on the development of next generation vaccines that are efficacious, but safe and more stable and cheaper to produce. Improved computational techniques and combined integrative strategies have the potential to simplify the process greatly. These techniques also have the potential to identify candidate proteins that would be overlooked by conventional experimentation. In particular, reverse vaccinology has proved effective in the discovery of antigenic subunit vaccines that would otherwise remain undiscovered. If methodology of reverse vaccinology is applied appropriately in vaccine design, it can save enormous amounts of money, time and labour.

    GAPS :

    Develop and register next generation vaccines that are safe, cheap to manufacture, stable and easy to produce.

  • Therapeutics

    Tetracyclines are the drugs of choice for treating avian chlamydiosis but treatment is often not capable to eliminate C. psittaci fully, especially in immuno-compromised birds.

    In vitro assays have been established for testing antibiotic susceptibility of C.psittaci, but they are all based on growth in cell cultures in the presence and absence (control) of the antibiotic. However, not all C.psittaci strains grow well in cell culture.

    GAPS :

    • Based on the emergence of tetracycline-resistant (TetR) Chlamydia trachomatis strains in humans and Chlamydia suis isolates in pig herds in several countries, it is of importance to investigate how the use of tetracyclines in ruminants and poultry could contribute (or has contributed) to the emergence and persistence of tetracycline-resistant C.psittaci strains.
    • A comprehensive genome analyses and comparisons of field C.psittaci isolates originating from flocks with common use of long-acting tetracycline should be performed to determine any possible occurrence of the Tet-genomic island, as found for C. suis infections in pigs. The latter can lead to treatment failures.
    • See also section 3. Pharmaceutical availability.

  • Biosecurity measures effective as a preventive measure

    • Use of a farm all-in, all-out management schedule to prevent infection in poultry.
    • Immunocompromised or immunosuppressed individuals should avoid contact with potentially infected animals or contaminated material.
    • Preventative measures should be put in place to limit the spread of infection from poultry and products of poultry to naïve animals and humans.
    • Adequate personal hygiene procedures including the use of protective equipment should be put in place to additionally reduce the risks of transmission to humans.

    GAPS :

    • Increase public awareness of the zoonotic potential of C.psittaci.
    • Knowledge of the risks arising from psittaci exposure emphasizes the essential need for modification and adaptation of work protocols and the strict observance of best practice to protect workers from exposure during work in the poultry industry (farms, hatcheries, slaughterhouses).

  • Border/trade/movement control sufficient for control

    To our knowledge only with respect to birds of the Psittacidae family (African & New World Parrots).

    • Veterinary authorities of countries free from avian chlamydiosis may prohibit importation or transit through their territory, from countries considered infected with avian chlamydiosis, of birds of the Psittacidae
    • Veterinary authorities of importing countries should require the presentation of an international veterinary certificate attesting that the birds:
      • Showed no clinical sign of avian chlamydiosis on the day of shipment.
      • Were kept under veterinary supervision for the 45 days prior to shipment and were treated against avian chlamydiosis using chlortetracycline.

  • Prevention tools

    GAPS :

    Need for a C.psittaci vaccine for poultry, pet birds and pigeons.

  • Surveillance

    Serological and molecular diagnostic surveillance to assess the status of poultry flocks, pet birds and pigeons.

    GAPS :

    Develop and recommendations for direct psittaci detection and sampling site.

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

    Vaccination ‘proof of concept’ for C.abortus demonstrates the feasibility of vaccination against C.psittaci.

    GAPS :

    Need for a C.psittaci vaccine for poultry, pet birds and pigeons.

  • Costs of above measures

    • For poultry, usually, controls are related to the flock and are not implemented at a national or regional level. Costs are related to diagnostic investigations and to treatment, as well as associated costs of dealing with mortality, lower end-weight, negative influence on feed conversion, carcass condemnation at slaughter ( C.psittaci).
    • For companion birds, controls are related to source tracing to prevent (further) zoonotic transmissions and depending on the case they might be implemented at regional of even cross-border level. Costs are related to mortality, diagnostic investigations (ompA genotyping PCR) in both birds and humans and to treatment and/or hospitalization of patients (also disability-adjusted life years or DALYs) .

  • Disease information from the WOAH

  • Disease notifiable to the WOAH

    • In many countries all over the world, psittacosis is a notifiable disease in humans and also in birds (avian chlamydiosis).
    • In accordance with List A, Annex I of Zoonoses Directive 2003/99/EC, data on animals, food and feed must be reported for the following eight zoonotic agents: Salmonella, Campylobacter, L. monocytogenes, Shiga toxin-producing Escherichia coli (STEC), Mycobacterium bovis, Brucella, Trichinella and Echinococcus. In addition, and based on the epidemiological situations in the MSs, data must be reported on the other agents and zoonoses (List B, Annex I of the Zoonoses Directive) including psittacosis and agents thereof. Furthermore, in accordance with Article 9 of the Directive, MSs shall assess the trends and sources of zoonoses, zoonotic agents and antimicrobial resistance in their territories and each MS shall send to the EC, every year by the end of May, a report on the trends in and sources of, zoonoses, zoonotic agents and antimicrobial resistance. Reports, and any summaries of them, shall be made publicly available.

    GAPS :

    • Despite List B, Annex I of the Zoonoses Directive, and article 9 of the Directive, epidemiological data on avian chlamydiosis is not available for all European countries and would be beneficial. Availability of data depends on disease surveillance systems in respective countries.
    • Improved monitoring of disease incidence is required.
    • Improved surveillance systems by veterinary laboratories/bodies at a local or national level are required.
    • Reporting of C.psittaci infections should be systematically done.
    • Increase systematic notification and investigation of chlamydiosis in all species to get a better understanding of prevalence.

  • WOAH disease card available

    Not available.

  • Socio-economic impact

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

    Psittacosis has been observed throughout the world. The disease occurs sporadically or in outbreaks, related to contact with infected pet birds or pigeons, visits to bird parks or bird exhibitions and/or related to occupational disease in veterinary facilities and poultry industry.Data from The Netherlands: disease burden caused by psittacosis estimated at 222 DALY per year (95% CI 172–280) over the period 2012–2014. This was comparable to the amount of DALYs estimated to be due to rubella or shigellosis in the same period in the Netherlands. According to their estimations, more than 1500 symptomatic psittacosis patients remained undiagnosed yearly in the Netherlands in 2012–2014.

    GAPS :

    • Requires better data on incidence for the pathogen.
    • Regarding C.psittaci, tetracyclines are the drugs of choice due to reported macrolide failures. Tetracyclines are however contraindicated for pregnant women and young children.

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

    Not known, might be higher as thought as the number of human infections are highly underestimated.

    GAPS :

    Requires better data on incidence to calculate costs of treatment for the pathogen.

  • Direct impact (a) on production

    Not known, might be higher as thought as the number of C.psittaci infections in birds are highly underestimated.

    GAPS :

    Impact of C.psittaci for poultry is highly underestimated.

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

    Costs associated with diagnostic testing as well as application and use of antibiotics contribute to the costs.

  • Indirect impact

    Less profit for the poultry farmer (loss between 1200 and 4900 euros per barn of 30,000 chickens during one production round; normally 6 to 7 production rounds per year depending on the type of farm).

  • Trade implications

  • Impact on international trade/exports from the EU

    EC no. 318/2007, came into force on July 1 in 2007, after being published in the Official Journal of the EU. This regulation lays down the animal health conditions for imports of certain birds from third countries and parts thereof into the EU. Thus, it is not applicable to: (a) poultry, (b) racing pigeons, (c) birds imported from Andorra, Liechtenstein, Monaco, Norway, San Marino, Switzerland and the Vatican City, and not to, (d) third countries which can use an animal health certificate referred to in Annex I of the regulation. The regulation also lays down the quarantine conditions. For instance: (1) approved quarantine facilities and centres; (2) direct transport of birds to quarantine stations; (3) attestation by the importers or their agents; (4) quarantine for at least 30 days; (5) examination, sampling and testing to be carried out by an official veterinarian; and (6) actions in case of disease suspicion, which are in case of chlamydiosis: treatment of all birds and prolonged quarantine for at least two months following the date of the last recorded case. Importantly, the regulation only allows imports of birds from approved breeding establishments, thus for birds other than poultry, only birds bred in captivity carrying an individual identification number and accompanied by an animal health certificate are allowed.

    GAPS :

    • Stricter (diagnostic) regulations on national and international bird trade, recording transactions are needed.
    • Testing of birds for C.psittaci before selling them in shops is highly advisable but not yet in place.

  • Impact on EU intra-community trade

    GAPS :

    Stricter (diagnostic) regulations on national and international bird trade within the EU are needed, recording transactions are needed.

  • Impact on national trade

    None

    GAPS :

    • Stricter (diagnostic) regulations on national and international bird trade within each country are needed, recording transactions are needed.
    • Testing of birds for C.psittaci before selling them in shops is highly advisable but not yet in place.

  • Links to climate

  • Seasonal cycle linked to climate

    There is currently no evidence for this, although changes in climate will likely affect persistence of C.psittaci in the environment.

    GAPS :

    Investigate the persistence of the agents in the environment.

  • Distribution of disease or vector linked to climate

    Unknown.

    GAPS :

    Investigate the persistence of the agents in ticks.

  • Outbreaks linked to extreme weather

    • Largely unknown
    • In the Netherlands and Sweden outbreaks of human psittacosis cases in winter have been reported. Birdfeeding and living on the countryside were among the encountered risk factors.

    GAPS :

    Weather could impact on persistence of organisms in the environment, with cooler weather resulting in organisms remaining viable for longer. Thus, persistence and viability of the pathogen in the environment under different climatic conditions should be investigated.

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

    Human psittacosis cases related to wild birds could potentially be changed by changing routes of migratory birds due to climate change.

  • Main perceived obstacles for effective prevention and control

    • Detecting the presence of the organism in subclinical persistently infected poultry, and birds in general, is currently impossible.
    • Many birds are carriers and treatment of persistent infections is extremely difficult.
    • Current diagnostic tests are mainly laboratory assays and culture requires BSL3 containment.
    • Insufficient knowledge on the molecular pathogenesis of different C.psittaci genotypes in birds.
    • Insufficient knowledge on the cellular and humoral immune response in different bird species.
    • No vaccines available.

    GAPS :

    • Better detection of latently/persistently infected poultry, pigeons and psittacine birds.
    • How to prevention infectious disease outbreaks due to the presence of carriers?
    • Sensitive and specific diagnostic point-of-care tests for both birds and humans.
    • Immunological toolbox for different bird species.
    • (Mucosal) next generation vaccines for mass application in poultry.
    • Next generation vaccines for pigeons and psittacine birds needed as C.psittaci in these birds presents a high zoonotic risk.
    • Designed vaccines should preferably be DIVA vaccines and complementary diagnostics for different bird species should be developed.

  • Main perceived facilitators for effective prevention and control

    • Improved diagnostic tests, including point-of-care tests.
    • Better understanding of the immune response to infection, in particular the protective elements of the immune response in different bird species
    • Improved next generation vaccines for C.psittaci.

    GAPS :

    • Improve our understanding of the immune correlates of protection (cellular and humoral responses) in different bird species.
    • Improve our understanding on mucosal immunology in different bird species.
    • Immunological toolbox for birds which are highly affected by C.psittaci, i.e., chickens, turkeys, ducks, geese, psittacine birds and pigeons.
    • Development of next generation vaccines for poultry, psittacine birds and pigeons.
    • Stricter regulations on bird trade and bird selling.
    • Improved diagnostic tests are available but better implementation of these diagnostic tests for monitoring and strict reporting according to national/international rules is needed.
    • Governmental support (regulation) for vaccination and diagnostic monitoring poultry, pigeons and in psittacine birds (health certificate), not only for animal welfare and reduction of economic loss, but also in relation to public health as C.psittaci is transmitted (mainly via aerosols) from birds to humans.

Global challenges

  • Antimicrobial resistance (AMR)

  • Impact of AMR on disease control

    Antibiotic resistance in Chlamydia spp. of animals and humans is increasing.

  • Established links with AMR in humans

    Antibiotic resistant genes are transferred in vitro from animal Chlamydia spp. to the human pathogen Chlamydia trachomatis.

    GAPS :

    Thus, awareness of possible transmission of antibiotic resistant genes during Chlamydia co-infections in animals and humans.

  • Digital health

  • Precision technologies available/needed

    What could lead to better poultry production:

    • From a production standpoint, individual real-time body weights, feed and water consumption.
    • From a husbandry and welfare perspective, knowing the stress levels in the bird and bird comfort assessed through body temperatures and air quality factors, such as carbon dioxide and ammonia.
    • From a disease management outlook, the ability to spot disease or find morbid birds before the entire flock is affected.
    • From a food processing perspective, increased yield.

    GAPS :

    • Technologies need to be validated to see if they are effective in increasing animal welfare and cost effective for the farmer.
    • Use of digital health should be further explored, for instance through bioaerosol monitoring to prevent spreading within the barn and zoonotic infections.

  • Data requirements

    N/A.

  • Data availability

    N/A.

  • Data standardisation

    N/A.

  • Climate change

  • Role of disease control for climate adaptation

    It could be assumed that improved disease control would positively impact the ability of birds to respond to climatic changes.

  • Effect of disease (control) on resource use

    If the presence of disease was lessened or eradicated, this would lead to less resource use for the same number of birds in a group with the same output.

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

    If the presence of disease was lessened or eradicated, this would likely result in less emissions and pollution for the same number of birds in a group with the same output.

  • Preparedness

  • Syndromic surveillance

    N/A.

  • Diagnostic platforms

    N/A.

  • Mathematical modelling

    Unknown.

    GAPS :

    Mathematical modelling would help to estimate economic losses in breeders, hatcheries, broilers and layers and thus understand the impact of disease outbreaks with different C.psittaci genotypes.

  • Intervention platforms

    WOAH, ECDC, national and regional level.

    GAPS :

    Room for improvement.

  • Communication strategies

    WOAH, ECDC, national and regional level.

    GAPS :

    Room for improvement.

Main critical gaps

    • Greater understanding of the extent of genetic diversity in C.psittaci strains.
    • Greater understanding of disease pathogenesis of C.psittaci in different bird species.
    • A greater understanding of the mechanistic basis of C.psittaci latency and persistence, including determination of the site of latency.
    • Evaluation of the resistance of C.psittaci under different environmental conditions.
    • Role of wildlife and vectors in transmission of C.psittaci infection.
    • Improve epidemiological knowledge of C.psittaci infections in humans.
    • Improve C.psittaci diagnostic tools, detecting latent/persistent infections; identifying naturally-infected animals in vaccinated flocks/populations; detecting co-infections; and point-of-care use. This will require greater standardisation of fully defined sera/DNA of known origin as well as pan-European inter-laboratory trials.
    • Further knowledge on relationships between antibiotics treatment (dose) and stage of C.psittaci persistence in the host.
    • Investigations on the potential emergence of antibiotic-resistant C.psittaci strains.
    • Development of an immunological toolbox for birds which are highly affected by psittaci, i.e., chickens, turkeys, ducks, geese, psittacine birds and pigeons.
    • Vaccine development studies: define immune correlates of protection for C.psittaci in different bird species.
    • Development of next generation C.psittaci marker vaccines, which will likely be based on subunit recombinant antigens, viral vectored vaccines and/or DNA or mRNA vaccines.
    • Governmental support (regulation) for vaccination and diagnostic monitoring poultry and in pet birds (health certificate), not only for animal welfare and reduction of economic loss, but also in relation to public health as C.psittaci is transmitted (mainly via aerosols) from birds to humans.

Conclusion

    • Better diagnostic tools are required, especially to identify C.psittaci latent carriers. Also, stricter regulations on bird trade and bird selling should be implemented, especially for psittacine pet birds.
    • Development of an immunological toolbox for birds which are highly affected by C.psittaci, e.g., chickens, turkeys, ducks, geese, psittacine birds and pigeons is urgently needed.
    • For C.psittaci, a biosafety level 3 and bioterrorism agent category B, the first vaccine still needs to be registered. Additional research is required to obtain this goal. The next generation of Chlamydia vaccines will be based on multi component recombinant antigens and/or probably viral vectored vaccines, DNA or mRNA. All these studies will be helped by a greater understanding of the pathogenesis of C.psittaci in different bird species, understanding the extent of genetic diversity amongst C.psittaci strains across Europe and developing tools to identify and manipulate targets for vaccine development studies.

Sources of information

  • Expert group composition

    Vanrompay Daisy, Ghent University, Ghent, Belgium – [Leader]

    Heddema Edou, Zuyderland Medical Center, The Netherlands

    Heijne Marloes, Wageningen University and Research, The Netherlands

    Jelocnik Martina, University of the Sunshine Coast, Sunshine Coast, Australia

    Laroucau Karine, Agence Nationale de Sécurité Sanitaire de l'Alimentation, de l'Environnement et du Travail, ANSES, Maisons-Alfort, France

    Lernout Tinne, Sciensano, Brussels, Belgium

    Longbottom David, Moredun Research Institute, Edinburgh, UK

    Schnee Christiane, Friedrich-Loeffler-Institute, Jena, Germany

    Szymanska-Czerwinska Monika, PIWet National Veterinary Research Institute, Pulawy, Poland

    Wattegedera Sean, Moredun Research Institute, Edinburgh, UK

  • Date of submission by expert group

    December 2023

  • References

    Appendix for sources of information and references is available from DISCONTOOLS secretariat.