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Wild birds are considered as a reservoir for avian chlamydiosis posing a potential infectious threat to domestic poultry and humans. Analysis of 894 cloacal or fecal swabs from free-living birds in Poland revealed an overall Chlamydiaceae prevalence of 14.8% (n = 132) with the highest prevalence noted in Anatidae (19.7%) and Corvidae (13.4%). Further testing conducted with species-specific real-time PCR showed that 65 samples (49.2%) were positive for C. psittaci whereas only one was positive for C. avium. To classify the non-identified chlamydial agents and to genotype the C. psittaci and C. avium-positive samples, specimens were subjected to ompA-PCR and sequencing (n = 83). The ompA-based NJ dendrogram revealed that only 23 out of 83 sequences were assigned to C. psittaci, in particular to four clades representing the previously described C. psittaci genotypes B, C, Mat116 and 1V. Whereas the 59 remaining sequences were assigned to two new clades named G1 and G2, each one including sequences recently obtained from chlamydiae detected in Swedish wetland birds. G1 (18 samples from Anatidae and Rallidae) grouped closely together with genotype 1V and in relative proximity to several C. abortus isolates, and G2 (41 samples from Anatidae and Corvidae) grouped closely to C. psittaci strains of the classical ABE cluster, Matt116 and M56. Finally, deep molecular analysis of four representative isolates of genotypes 1V, G1 and G2 based on 16S rRNA, IGS and partial 23S rRNA sequences as well as MLST clearly classify these isolates within the C. abortus species. Consequently, we propose an expansion of the C. abortus species to include not only the classical isolates of mammalian origin, but also avian isolates so far referred to as atypical C. psittaci or C. psittaci/C. abortus intermediates.

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.

Chlamydiaceae occurrence has been largely evaluated in wildlife, showing that wild birds are efficient reservoirs for avian chlamydiosis. In this study, DNA extracted from cloacal swabs of 108 corvids from Northeast Italy was screened for Chlamydiaceae by 23S real-time (rt)PCR. The positive samples were characterised by specific rtPCRs for Chlamydia psittaci, Chlamydia abortus, Chlamydia gallinacea, Chlamydia avium, Chlamydia pecorum and Chlamydia suis. Cloacal shedding of Chlamydiaceae was detected in 12 out of 108 (11.1%, 5.9%–18.6% 95% CI) corvids sampled. Molecular characterisation at the species level was possible in 8/12 samples, showing C. psittaci positivity in only one sample from a hooded crow and C. abortus positivity in seven samples, two from Eurasian magpies and five from hooded crows. Genotyping of the C. psittaci-positive sample was undertaken via PCR/high-resolution melting, clustering it in group III_pigeon, corresponding to the B genotype based on former ompA analysis. For C. abortus genotyping, multilocus sequence typing was successfully performed on the two samples with high DNA load from Eurasian magpies, highlighting 100% identity with the recently reported Polish avian C. abortus genotype 1V strain 15-58d44. To confirm the intermediate characteristics between C. psittaci and C. abortus, both samples, as well as two samples from hooded crows, showed the chlamydial plasmid inherent in most C. psittaci and avian C. abortus, but not in ruminant C. abortus strains. The plasmid sequences were highly similar (≥99%) to those of the Polish avian C. abortus genotype 1V strain 15-58d44. To our knowledge, this is the first report of avian C. abortus strains in Italy, specifically genotype 1V, confirming that they are actively circulating in corvids in the Italian region tested.

The presence and zoonotic transfer of four different avian Chlamydia spp. was assessed in an epidemiological study in a psittacine bird population and its owners. Fecal swabs from 84 pet birds and pharyngeal swabs from 22 bird owners were collected from 21 locations in Flanders. Samples were examined using established and novel PCR platforms combined with culture on PCR-positive samples. Chlamydiaceae DNA was detected in 33 of 84 (39.3%) birds. The predominant part of the avian infections could be attributed to C. psittaci (22 of 84; 26.2%), followed by C. avium (11 of 84; 13.1%). C. gallinacea and C. abortus were not detected in birds or humans. C. psittaci was the only species detected in pet bird owners (4 of 22; 18.2%), stressing its zoonotic importance. This study showed that C. psittaci and the more recently discovered novel avian species C. avium are undoubtedly present in the Flemish psittacine bird population. Our results justify additional research in a larger psittacine bird population and its owners, focusing on C. psittaci and C. avium. In the meantime, increased awareness among pet bird owners and the implementation of preventive measures in the pet bird industry is advised to limit the circulation of established and novel emerging avian chlamydial species.

The aims of the present study were to assess the prevalence of Chlamydia suis in an Italian pig herd, determine the tetracycline susceptibility of C. suis isolates, and evaluate tet(C) and tetR(C) gene expression. Conjunctival swabs from 20 pigs were tested for C. suis by real-time polymerase chain reaction, and 55% (11) were positive. C. suis was then isolated from 11 conjunctival swabs resampled from the same herd. All positive samples and isolates were positive for the tet(C) resistance gene. The in vitro susceptibility to tetracycline of the C. suis isolates showed MIC values ranging from 0.5 to 4 μg/mL. Tet(C) and tetR(C) transcripts were found in all the isolates, cultured both in the absence and presence of tetracycline. This contrasts with other Gram-negative bacteria in which both genes are repressed in the absence of the drug. Further investigation into tet gene regulation in C. suis is needed.

The cultivation of Chlamydia gallinacea, a recently identified species, is challenging due to the lack of an optimized protocol. In this study, several infection protocols were tested, including different cell lines, incubation temperatures, centrifugation methods and culture media. However, none were successful in field samples. The only exception was a chance co-culture with Trichosporon asahii, a microorganism commonly found in the chicken gut. This suggests that current in vitro methods may not be optimized for this species and that host-associated microorganisms may influence the in vivo growth of C. gallinacea, which is typically found in the chicken gut. These findings raise new questions and highlight the need for further investigation of microbial interactions within the host, particularly to understand their role in the proliferation of chlamydial species.

Chlamydia (C.) psittaci is the causative agent of avian chlamydiosis and human psittacosis. In this study, we extracted single-nucleotide polymorphisms (SNPs) from the whole genome sequences of 55 C. psittaci strains and identified eight major lineages, most of which are host-related. A combined PCR/high-resolution melting (HRM) assay was developed to screen for eight phylogenetically informative SNPs related to the identified C. psittaci lineages. The PCR-HRM method was validated on 11 available reference strains and with a set of 118 field isolates. Overall, PCR-HRM clustering was consistent with previous genotyping data obtained by ompA and/or MLST analysis. The method was then applied to 28 C. psittaci-positive samples from animal or human cases. As expected, PCR-HRM typing results from human samples identified genotypes linked to ducks and pigeons, a common source of human exposure, but also to the poorly described Mat116-like genotype. The new genotyping method does not require time-consuming sequencing and allows a quick identification of the source of infection.

Background Melioidosis, an emerging infectious disease that affects both humans and animals, is caused by the soil-dwelling bacterium Burkholderia pseudomallei. It is endemic in South and Southeast Asia, and northern Australia, causing an estimated 165,000 human cases annually worldwide. Human cases have been reported in the French West Indies (Martinique and Guadeloupe) since the 1990s. Conversely, no human cases have been reported in French Guiana, a French territory in South America. Our study aimed to investigate whether B. pseudomallei is locally established in Guadeloupe and French Guiana using animals as a proxy. Methodology/principal findings Blood samples were collected from different animals from 56 farms in French Guiana (n = 670) and from two goat farms in Les Saintes (n = 31), part of the archipelago of Guadeloupe and tested by enzyme-linked immunosorbent assay (ELISA). In Les Saintes, a serological follow-up was performed, and soil, water and goat rectal swabs were collected and analyzed by culture and PCR. The highest seroprevalence rates (39%) were observed in goats in Les Saintes, followed by horses (24%) and cattle (16%) in French Guiana. In the two goat farms, supplementary analyses detected B. pseudomallei from one goat rectal swab, and a B. pseudomallei strain was isolated from the soil. Conclusions/significance Our animal serological data suggest the presence of B. pseudomallei in Les Saintes and French Guiana. In Les Saintes, environmental surveys confirmed the endemicity of the bacteria, which is consistent with documented human cases of melioidosis on the island. We did not conduct an environmental survey in French Guiana. Nevertheless, our serological results call for local environmental surveys and a retrospective reassessment of human infections with melioidosis-like symptoms.

Chlamydiaceae are obligatory intracellular bacteria causing acute and chronic diseases in animals and humans worldwide, with recently discovered species with a still unclear pathogenic potential (i.e., C. gallinacea). In Italy, Chlamydiaceae infections are underestimated both in animals and humans. To estimate the prevalence of Chlamydiaceae species in poultry and occupationally exposed workers on farm, a cross-sectional study was carried out in north-western Italy. A total of 2063 samples from 83 commercial and 31 backyard poultry farms were analysed using real-time PCRs for Chlamydiaceae screening and species typing. Chlamydiaceae were detected in 23 farms, with a herd prevalence of 20.2% (95%CI: 13.2–28.7), higher in backyard farms (38.7%; 95%CI: 21.8–57.8) compared to commercial ones (13.3%; 95%CI: 6.8–22.5). C. gallinacea was found in 18 chicken farms, both commercial and backyard, and C. psittaci only in 3 backyard farms. Exposure to wild birds and factors related to biosecurity resulted the main risk factors associated with Chlamydia positivity. Out of the 113 sputum samples collected from farmers, 16 tested positive to Chlamydiaceae, with a prevalence of 14.2% (95%CI: 8, 3–22). To the best of our knowledge, for the first time at international level, C. gallinacea was detected in humans with farmer positivity associated with farm infectious status, suggesting a bird-to-human transmission.

Avian chlamydiosis is an infection caused by obligate intracellular, gram-negative bacteria belonging to the Chlamydiaceae family. Birds can be hosts of several Chlamydia species, including Chlamydia avium, which has only been detected in pigeons and psittacine birds. In this study, depression, respiratory distress, and mortality were noted among psittacines belonging to a large aviary with 35 different avian species. On the basis of immunohistochemistry and PCR testing, chlamydiosis was diagnosed in affected birds. Gross and histopathologic lesions were mainly observed in the spleen and gastrointestinal tract. Chlamydia avium was detected in four psittacines by PCR, including two dead birds and two individuals exhibiting respiratory distress. Increased aspartate aminotransferase and lactate dehydrogenase values and anemia were consistently identified in affected birds. Administration of doxycycline, combined with hepatoprotectors and vitamins, was effective in stopping mortality and bacterial shedding.