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Background Migratory birds serve as potential hosts for ticks and can be reservoirs of tick-borne pathogens (TBPs). The aim of our study was to investigate the prevalence of TBPs in juvenile Ixodes ricinus collected from Erithacus rubecula , Turdus merula , and Turdus philomelos passing through the Vistula River Valley, Poland — one of the most important European north-south routes for migratory birds. Methods To detect TBPs in collected ticks we used a high-throughput microfluidic real-time PCR method. In addition, we performed a phylogenetic analysis of Borreliella garinii flaB and Rickettsia helvetica ompB sequences, considering haplotype diversity through a Median Joining Network. Results Our results showed a high prevalence and wide spectrum of TBPs in both larvae and nymphs of I. ricinus . Overall, including co-infections, 47.41% of the tested tick specimens were infected with at least one TBP. Borreliaceae spirochetes were detected in ticks collected from all examined bird species. Ticks (larvae and nymphs) collected from T. merula showed the highest prevalence of Bo. garinii (33.33%), Bo. burgdorferi s.s. (7.69%) and Borrelia miyamotoi (2.56%), while the highest number of ticks infected with Bo. valaisiana were collected from T. philomelos (8.11%). In turn, the highest prevalence of R. helvetica (20.00%) was observed in ticks collected from E. rubecula . Additionally, infections with A. phagocytophilum (5.00%), Ehrlichia spp. (2.50%), Ba. divergens (2.50%) and Ba. venatorum (2.50%) were only confirmed in ticks collected from this bird species. The phylogenetic analysis of Bo. garinii revealed that the detected haplotype circulates widely across various hosts and is geographically widespread, while the haplotype of R. helvetica is mainly detected in ticks in Central Europe. Conclusions Ticks carried by T. merula , T. philomelos , and E. rubecula migrating along the Vistula River Valley, Poland are characterized by a high prevalence and a wide spectrum of detected TBPs. Tested ticks carry widespread strains of Bo. garinii , in contrast to R. helvetica , which is mainly found in Central Europe. Therefore, further research on the possible role of birds as reservoirs of TBPs is needed.

Eimeria species cause the intestinal disease coccidiosis, most notably in poultry. While the direct impact of coccidiosis on animal health and welfare is clear, its influence on the enteric microbiota and by-stander effects on chicken health and production remains largely unknown, with the possible exception of Clostridium perfringens (necrotic enteritis). This study evaluated the composition and structure of the caecal microbiome in the presence or absence of a defined Eimeria tenella challenge infection in Cobb500 broiler chickens using 16S rRNA amplicon sequencing. The severity of clinical coccidiosis in individual chickens was quantified by caecal lesion scoring and microbial changes associated with different lesion scores identified. Following E. tenella infection the diversity of taxa within the caecal microbiome remained largely stable. However, infection induced significant changes in the abundance of some microbial taxa. The greatest changes were detected in birds displaying severe caecal pathology; taxa belonging to the order Enterobacteriaceae were increased, while taxa from Bacillales and Lactobacillales were decreased with the changes correlated with lesion severity. Significantly different profiles were also detected in infected birds which remained asymptomatic (lesion score 0), with taxa belonging to the genera Bacteroides decreased and Lactobacillus increased. Many differential taxa from the order Clostridiales were identified, with some increasing and others decreasing in abundance in Eimeria-infected animals. The results support the view that caecal microbiome dysbiosis associated with Eimeria infection contributes to disease pathology, and could be a target for intervention to mitigate the impact of coccidiosis on poultry productivity and welfare. This work highlights that E. tenella infection has a significant impact on the abundance of some caecal bacteria with notable differences detected between lesion score categories emphasising the importance of accounting for differences in caecal lesions when investigating the relationship between E. tenella and the poultry intestinal microbiome.

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.

Anthropogenic food provisioning of wildlife can alter the frequency of contacts among hosts and between hosts and environmental sources of pathogens. Despite the popularity of garden bird feeding, few studies have addressed how feeders influence host contact rates and disease dynamics. We experimentally manipulated feeder density in replicate aviaries containing captive, pathogen-naive, groups of house finches (Haemorhous mexicanus) and continuously tracked behaviours at feeders using radio-frequency identification devices. We then inoculated one bird per group with Mycoplasma gallisepticum (Mg), a common bacterial pathogen for which feeders are fomites of transmission, and assessed effects of feeder density on house finch behaviour and pathogen transmission. We found that pathogen transmission was significantly higher in groups with the highest density of bird feeders, despite a significantly lower rate of intraspecific aggressive interactions relative to the low feeder density groups. Conversely, among naive group members that never showed signs of disease, we saw significantly higher concentrations of Mg-specific antibodies in low feeder density groups, suggesting that birds in low feeder density treatments had exposure to subclinical doses of Mg. We discuss ways in which the density of garden bird feeders could play an important role in mediating the intensity of Mg epidemics. This article is part of the theme issue ‘Anthropogenic resource subsidies and host–parasite dynamics in wildlife'.

Background Gallibacterium anatis (G. anatis ), a microorganism of the Pasteurellaceae family, is an emerging avian pathogen associated with reproductive and respiratory diseases in poultry. However, its role in ornamental birds is still poorly understood. The aim of the present study was to conduct the first comprehensive survey of the prevalence of G. anatis in pet birds, to investigate its antimicrobial resistance (AMR) profile and to assess its ability to form biofilms using cultural, biochemical, molecular and histopathological methods. Methods In this study, 191 fecal and tissue samples were collected from various companion birds. Clinical samples were cultured on 5% sheep blood agar and MacConkey agar plates to isolate bacterial pathogens. After incubation, colonies were evaluated based on their macroscopic characteristics such as size, color, and hemolytic properties on blood agar-and a Gram stain was performed as an essential preliminary step for bacterial identification. The 16–23 S rRNA gene region of G. anatis was amplified by PCR method. The disc diffusion method was used to assess microbial susceptibility and resistance. Biofilm formation was analyzed using a microtiter plate assay. Tissue samples were routinely processed, embedded in paraffin, sectioned and stained with common haematoxylin-eosin (H&E). Results In this study, 20 G. anatis strains were isolated from 191 clinical samples of pet birds, representing a prevalence of 10.5%. Isolates were identified by colony morphology, Gram staining, biochemical testing and PCR for the –intergenic spacer region of 16–23 S rRNA, which yielded diagnostic amplicons of 790 bp and 1080 bp. Antimicrobial susceptibility testing showed complete susceptibility to ciprofloxacin (100%) and remarkable resistance to erythromycin (80%). β-lactam resistance was prevalent, with 70% and 75% of isolates resistant to ampicillin and amoxicillin, respectively. Biofilm formation tests showed that 80% of isolates had moderate biofilm formation. Gross and histopathological examinations of infected birds revealed severe respiratory and systemic lesions, including tracheitis, bronchopneumonia with focal necrosis, multifocal hepatic necrosis, and vascular congestion in multiple organs. Conclusions These results support the idea that G. anatis is a potentially important pathogen, with a biofilm-forming ability that contributes to treatment failure and environmental persistence. The 45% prevalence of multidrug resistance (MDR) highlights the pressing need for antimicrobial stewardship in avian veterinary medicine. Given the zoonotic potential of G. anatis , our study underscores the importance of One Health surveillance efforts in mitigating risk to both poultry and humans.

Psittacosis, or parrot fever, is a zoonotic disease caused by Chlamydia species associated with birds. One of the causative agents of the disease is Chlamydia psittaci , which is commonly carried by psittacine and other bird species, can be highly pathogenic and virulent to humans. In Hong Kong, a city with high population density, psittacosis is a notifiable disease with over 60% of cases in the last decade resulting in hospitalization. However, the sources of transmission of C . psittaci and its prevalence in pet birds in Hong Kong are currently unknown. To evaluate the risks of psittacosis transmission through pet birds, we tested the presence of C . psittaci and determined its genotypes in samples obtained from 516 captive birds from households, pet shops, and a veterinary hospital in Hong Kong. Results revealed that five samples (0.97%), collected from budgerigars and cockatiels, were C . psittaci -positive, while four (80%) of them were obtained from pet shops. Our phylogenetic analysis revealed that all identified strains belonged to Genotype A and showed high similarity to other sequences of this genotype obtained from various geographical locations and host species, including mammals. Our findings provide evidence for the presence of Chlamydia psittaci and shed light on its sources in captive birds in Hong Kong. They highlight the potential zoonotic risks associated with this pathogen, which can affect both humans and wild birds.

Background The tropical climate and diverse vector community allows the Rio Grande Valley (RGV) of South Texas to support many vector-borne pathogen transmission cycles. It is a key area for monitoring bird ticks, since most of the migratory birds fly through this corridor to move for south tropical latitudes. Some of the tick species that infest birds in Texas can also transmit tick-borne pathogens that concern public health. Methods During bird banding activities in 2019–2024, ticks were collected opportunistically from local and migrant birds, as well as from outdoor recreationalists, to explore the presence of tick-borne pathogens. Applying a polymerase chain reaction (PCR)-DNA sequencing approach, ticks were tested for Ehrlichia and Rickettsia species. Results Of 375 ticks, eight tick species were identified, including species regarded as locally established ( Amblyomma inornatum , Amblyomma maculatum , Amblyomma mixtum , Amblyomma tenellum , and Dermacentor variabilis ), neotropical species imported by migratory birds ( Amblyomma geayi and Amblyomma longirostre ), and for the first time in Texas, Ixodes keiransi , formerly the North American lineage of Ixodes affinis . Amblyomma tenellum was the most abundant tick species (89.3%). All ticks were screened for Ehrlichia , resulting in Ehrlichia chaffeensis detection in three A. tenellum ticks (one nymph and two adults) found on humans, and one positive for Ehrlichia ewingii in an A. inornatum nymph collected from a Clay-colored Thrush ( Turdus grayi ). Both bacteria can cause human ehrlichiosis, which is infrequently reported in Texas. The Rickettsia screening of ticks resulted in detection of Rickettsia amblyommatis , a potentially pathogenic spotted fever group Rickettsia , in nine ticks: eight A. inornatum ticks (one larva, five nymphs and two adults), seven of which were collected from Long-billed Thrashers ( Toxostoma longirostre ); and an A. longirostre engorged nymph from an Acadian Flycatcher ( Empidonax virescens ). Conclusions Our results highlight the importance of occupational exposure to ticks and the potential public health impact of the relatively neglected human-biting vector, A. tenellum. . There is also a critical need to investigate the fate of bird-imported A. inornatum and A. longirostre , and the pathogens they carry. Graphical Abstract

Partially protective vaccination can sometimes select for increasingly virulent pathogens. Fleming-Davies et al. asked what happens in a natural system. In the United States, the house finch population is suffering an increasingly virulent epidemic caused by Mycoplasma gallisepticum . The pathogen induces incomplete immunity that clears less virulent pathogens and offers partial protection against strains of greater virulence. In the birds, the partial immune response does away with competition from the less virulent pathogens. The partial immunity of the host also hinders replication of the more virulent pathogens enough to allow some birds to survive. This allows increasingly virulent forms of the pathogen to be transmitted. Science , this issue p. 1030 A study of house finches and their bacterial pathogen Mycoplasma gallisepticum elucidates how virulence is enhanced. Immune memory evolved to protect hosts from reinfection, but incomplete responses that allow future reinfection may inadvertently select for more-harmful pathogens. We present empirical and modeling evidence that incomplete immunity promotes the evolution of higher virulence in a natural host-pathogen system. We performed sequential infections of house finches with Mycoplasma gallisepticum strains of various levels of virulence. Virulent bacterial strains generated stronger host protection against reinfection than less virulent strains and thus excluded less virulent strains from infecting previously exposed hosts. In a two-strain model, the resulting fitness advantage selected for an almost twofold increase in pathogen virulence. Thus, the same immune systems that protect hosts from infection can concomitantly drive the evolution of more-harmful pathogens in nature.

Escherichia coli sequence type 131:H:22 is a consequential lineage of extraintestinal pathogenic E. coli, associated with human pyelonephritis and sepsis. We report the transmission of avian pathogenic E. coli in a parrot rehabilitation center in Brazil and the presence of a high-risk zoonotic lineage of extraintestinal pathogenic E. coli sequence type 131-H22.