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In 2021, a novel group of Chlamydia strains in wild birds was classified as avian Chlamydia abortus, with unknown zoonotic potential. We report relevant features of avian C abortus infections from a Dutch family cluster and unrelated historical cases using clinical, epidemiological, and microbiological data. An outbreak of avian C abortus started in the Netherlands in December, 2022. Source investigation was done using questionnaires to interview patients and environmental sampling. The outbreak strain of avian C abortus was cultured from three patients from whom sufficient material was available for culture and underwent whole-genome analysis. The outbreak strains and retrospective cohort study strains previously submitted to the National Human Psittacosis surveillance programme in the Netherlands between 2010 and 2022 were typed by partial ompA sequencing. Strains with the same aberrant ompA genotype were further analysed with XerC gene plasmid analysis and compared with closely related Chlamydia sequences available in GenBank. An avian C abortus strain caused a cluster of respiratory illness in four family members. Three patients were hospitalised with community-acquired pneumonia, one of whom was admitted to the intensive care unit. The faeces of wild birds were considered a probable source for the index infection. For two family members, human-to-human transmission was a plausible route. Ten historical cases could be identified with avian C abortus with the same ompA genotype. All patients had been admitted to hospital, at least five developed pneumonia, and one died. This cluster supports that avian C abortus strains can cause human infections and underlines that human-to-human transmission should be considered when tracing the source of such infections. National Institute for Public Health and the Environment and Dutch Ministry of Agriculture, Fisheries, Food Security and Nature. For the Dutch translation of the abstract see Supplementary Materials section.

ABSTRACT The iconic Australian marsupial, the koala (Phascolarctos cinereus), has suffered dramatic population declines as a result of habitat loss and fragmentation, disease, vehicle collision mortality, dog attacks, bushfires and climate change. In 2012, koalas were officially declared vulnerable by the Australian government and listed as a threatened species. In response, research into diseases affecting koalas has expanded rapidly. The two major pathogens affecting koalas are Chlamydia pecorum, leading to chlamydial disease and koala retrovirus (KoRV). In the last eight years, these pathogens and their diseases have received focused study regarding their sources, genetics, prevalence, disease presentation and transmission. This has led to vast improvements in pathogen detection and treatment, including the ongoing development of vaccines for each as a management and control strategy. This review will summarize and highlight the important advances made in understanding and combating C. pecorum and KoRV in koalas, since they were declared a threatened species. With complementary advances having also been made from the koala genome sequence and in our understanding of the koala immune system, we are primed to make a significant positive impact on koala health into the future. Recent advances in understanding the two major pathogens of koalas, Chlamydia pecorum and koala retrovirus (KoRV), have benefited both koala conservation and general chlamydial and retroviral research fields.

Several infectious agents concurrently infect wild koalas and so, as for similar agents in other species, co-infection interactions could affect disease presentation and clinical outcomes. This study determines the frequency of circulating and mucosal Chlamydia pecorum infections along with phascolarctid herpesvirus (PhaHV), Koala retrovirus (KoRV), and trypanosome infections in 115 wild koalas admitted to wildlife hospitals in the Australian states of Queensland and New South Wales. C. pecorum, PhaHV, trypanosomes, and KoRV (endogenous subtype A and exogenous subtype D) were detected in 61.1%, 68.9%, 63.3% and 100% of the individuals sampled, respectively. The co-infection relationships identified generate hypotheses for the observed variation in disease presentations in that they resemble co-infection interactions that drive the variations in presentation and response to treatment for chlamydiosis in other species, including humans. Among koalas with chlamydiosis, PhaHV-1 mucosal shedding positively predicted euthanasia on admission, and accounting for Trypanosome irwini infection status improved the model quality. Additionally, in female koalas, the detection of mucosal PhaHV-1 and greater KoRV proviral pol loads were equal predictors of chlamydial reproductive disease. While the detection frequency of C. pecorum, PhaHV-1, PhaHV-2, and T. gilletti in circulation were low, cases with circulating C. pecorum and without mucosal C. pecorum shedding or clinical chlamydiosis were observed presenting an important consideration for future diagnostic testing. This study serves as a basis for investigating co-infection interaction pathways through mechanistic studies to determine their effect on pathogenesis of chlamydiosis, improve our understanding of host-pathogen-environment dynamics impacting the koala, and identify novel intervention and screening methods.

Recent outbreaks of highly pathogenic avian influenza in Europe have raised questions regarding the epidemiological role of commensal wild birds on free-range poultry farms. This study aimed to assess the prevalence of avian influenza viruses (AIV), avulaviruses, coronaviruses and Chlamydia sp. in commensal wild birds on a free-range duck farm in southwestern France and to evaluate possible transmission events at the wild‒domestic interface. From 2019 through 2021, a longitudinal study was conducted on wild birds, domestic ducks and their shared environment on farms. Commensal wild birds were captured and sampled for blood and swabs, and fresh feces from cattle egrets visiting the farm were collected. In parallel, domestic ducks were sampled, and environmental samples were collected. The presence of the four pathogens was tested by q(RT-)PCR, and the immunity of wild birds to AIV and Newcastle disease virus (NDV) was tested by ELISA. Wild birds were found to shed AIV and Chlamydia only, with a low prevalence (< 3%). The seroprevalence rates were less than 10% for AIV and less than 4.5% for NDV. No significant temporal trend was identified. Ducks and their environment frequently test simultaneously positive for the same pathogens (19 to 44% of flocks), mostly during fall‒winter. In addition to unrelated temporal patterns, the identification of pathogens in wild birds seemed unrelated to that in domestic ducks. These results suggest a low transmissibility of the avian pathogens tested in our study at the wild‒domestic interface and highlight the limited contribution of commensal wild birds in comparison with free-range poultry to the global microbiological pressure on the environment.

Chlamydia abortus causes enzootic abortion in sheep and poses a zoonotic public health threat. Since chlamydiosis leads to significant economic losses, this cross-sectional sero-epidemiological study was conducted to determine the prevalence of antibodies against Chlamydia abortus in ewe flocks with a history of abortion from the district Layyah of Pakistani Punjab. For this purpose, 184 serum samples were tested from 50 privately owned sheep flocks located across three sub districts (Tehsils) by commercially available iELISA kit. The seroprevalence (%) along with 95% confidence intervals (CI) were calculated, and potential risk factors were analysed. A 25.8% (CI 15.2–39.6) flock-based and 7.9% (CI 4.4–12.6) individual-based true seroprevalence was observed. The highest seroprevalence was recorded in Tehsil Layyah (58.7% flock-level and 18.5% individual-level) followed by Karor Lal Esan (17.4% flock-level and 4.7% individual-level), whereas no flock was found positive in Tehsil Choubara. The association of potential risk factors; age group, flock size, feeding system, rearing system, species and breeds, with seropositivity was determined by chi-square testing. Only the history of abortions was found to be significantly (OR: 11.0, p  < 0.001) associated with the higher seroprevalence in the sampled flocks. This study is the first to document the seroprevalence of ovine enzootic abortion from the district of Layyah, and we recommend further investigations and extension efforts to consider a control strategy in affected flocks.

Chlamydia pecorum is a globally endemic livestock pathogen but prevalence data from Switzerland has so far been limited. The present longitudinal study aimed to get an insight into the C . pecorum prevalence in Swiss cattle and investigated infection dynamics. The study population consisted of a bovine herd (n = 308) located on a farm in the north-eastern part of Switzerland. The herd comprised dairy cows, beef cattle and calves all sampled up to five times over a one-year period. At each sampling timepoint, rectal and conjunctival swabs were collected resulting in 782 samples per sampled area (total n = 1564). Chlamydiaceae screening was performed initially, followed by C . pecorum -specific real-time qPCR on all samples. For C . pecorum -positive samples, bacterial loads were determined. In this study, C . pecorum was the only chlamydial species found. Animal prevalences were determined to be 5.2–11.4%, 38.1–61.5% and 55–100% in dairy cows, beef cattle and calves, respectively. In all categories, the number of C . pecorum -positive samples was higher in conjunctival (n = 151) compared to rectal samples (n = 65), however, the average rectal load was higher. At a younger age, the chlamydial prevalence and the mean bacterial loads were significantly higher. Of all sampled bovines, only 9.4% (29/308) were high shedders (number of copies per μl >1,000). Calves, which tested positive multiple times, either failed to eliminate the pathogen between sampling timepoints or were reinfected, whereas dairy cows were mostly only positive at one timepoint. In conclusion, C . pecorum was found in healthy Swiss cattle. Our observations suggested that infection takes place at an early age and immunity might develop over time. Although the gastrointestinal tract is supposed to be the main infection site, C . pecorum was not present in rectal samples from dairy cows.

Chlamydiosis is the major infectious disease responsible for significant morbidity and mortality in free-living koalas. Recently, it was reported that 28.5% of koalas infected with chlamydiosis were presented with no overt clinical signs. Identification and quantification of changes in plasma biomarkers’ fluctuations have the potential to enhance C . pecorum detection and facilitate the monitoring of therapeutic efficacy of antibiotics to treat this disease in koalas. Therefore, concentrations of the essential amino acid tryptophan, tryptophan’s metabolite kynurenine, and the kynurenine:tryptophan ratio were quantified by high-performance liquid chromatography in the plasma of clinically normal koalas (n = 35), koalas identified with chlamydial disease (n = 35) and koalas that had other non-chlamydial co-morbidities (n = 10). Results showed that there was a significant difference between the clinically normal versus diseased, and clinically normal versus ‘other’ (both p < 0.001) in kynurenine plasma concentrations and kynurenine:tryptophan ratio; and also between the clinically normal and diseased in tryptophan plasma concentrations (p = 0.001). Proposed reference ranges of tryptophan, kynurenine, and kynurenine:tryptophan ratio in koalas are: 4.27–10.4 μg/mL, 0.34–1.23 μg/mL, and 0.05–0.22, respectively. Proposed optimal cut-off points to differentiate between clinically normal and diseased are: ≤ 4.75 μg/mL (tryptophan), ≥ 0.88 μg/mL (kynurenine), and ≥ 0.12 (kynurenine:tryptophan); and ≤ 7.67 μg/mL (tryptophan), ≥ 1.18 μg/mL (kynurenine), and ≥ 0.16 (kynurenine:tryptophan) to differentiate between released/recovered and euthanised of the diseased/‘other’ koalas. Significant differences in haematological and biochemical analytes were in the plasma globulins between the clinically normal and diseased koalas (p = 0.01), and in alkaline phosphatase between the clinically normal and ‘other’ koalas (p = 0.03). Although these potential biomarkers, especially tryptophan, may not be specific for detecting C . pecorum from the rest of the population, kynurenine and the kynurenine:tryptophan ratio may have a role in identifying unhealthy koalas from the clinically normal ones, irrespective of the underlying cause.

Abortion is one of the major threats to the livestock industry, and it also poses significant threats to public health since some of the abortifacient agents are considered zoonotic. Chlamydia abortus (C. abortus), Coxiella burnetii (C. burnetii), Listeria monocytogenes (L. monocytogenes), and Cache Valley virus (CVV) are recognized as important zoonotic and abortifacient agents of reproductive failure in small ruminants. This study determined the prevalence of these agents in ovine and caprine foetuses in Türkiye. A total of 1 226 foetuses were collected from the sheep (n = 1 144) and goats (n = 82) from different flocks between 2012 and 2017. Molecular detection methods were used to detect C. abortus, C. burnetii, and L. monocytogenes DNA and CVV RNA in aborted foetuses. In this study, C. abortus was the most prevalent abortifacient agent among the investigated ovine (264/1144) and caprine (12/82) foetuses, followed by C. burnetii with a frequency of 2.8% (32/1144) and 8.5% (7/82) in ovine and caprine foetuses, respectively. L. monocytogenes DNA was detected in 28 (2.4%) and 2 (2.4%) of the ovine and caprine foetuses, respectively. However, CVV RNA was not detected. Although the predominant mixed infection was C. abortus and C. burnetii, mixed infection of C. abortus and L. monocytogenes, and C. burnetii and L. monocytogenes were also found. The information presented in this study contributes to the understanding of the roles of C. abortus, C. burnetii, L. monocytogenes, and CVV in abortions in small ruminants, and could be beneficial for developing more effective control strategies.

Investigations conducted on feral African Sacred Ibises (Threskiornis aethiopicus) in western France led to the isolation of a strain with chlamydial genetic determinants. Ultrastructural analysis, comparative sequence analysis of the 16S rRNA gene, ompA, and of a concatenate of 31 highly conserved genes, as well as determination of the whole genome sequence confirmed the relatedness of the new isolate to members of the Chlamydiaceae, while, at the same time demonstrating a unique position outside the currently recognized species of this family. We propose to name this new chlamydial species Chlamydia ibidis.

Chlamydia pecorum is an established and prevalent infection that produces severe clinical disease in many koala populations, contributing to dramatic population declines. In wild South Australian koala populations, C . pecorum occurrence and distribution is unknown. Here, C . pecorum- specific real-time quantitative PCR (qPCR) was applied to ocular and urogenital swabs from targeted surveys of wild koalas from the mainland Mount Lofty Ranges (MLR) (n = 75) and Kangaroo Island (KI) (n = 170) populations. Historical data from 13,081 KI koalas (1997–2018) provided additional evidence for assessing the absence of C . pecorum infection. In the MLR population, 46.7% (CI: 35.1–58.6%) of koalas were C . pecorum positive by qPCR but only 4% had grade 3 clinical disease. MLR koala fertility was significantly reduced by C . pecorum infection; all reproductively active females (n = 16) were C . pecorum negative, whereas 85.2% of inactive females (n = 23) were positive (P < 0.001). KI koalas were C . pecorum negative and the population was demonstrated to be free of C . pecorum infection with 95% confidence. C . pecorum is a real threat for the sustainability of the koala and KI is possibly the last isolated, large C . pecorum -free population remaining in Australia. These koalas could provide a safeguard against this serious disease threat to an iconic Australian species.