Prevalence of Mycoplasma spp., Chlamydia spp., and Moraxella species in ocular samples from European bison (Bison bonasus) and their association with infectious keratoconjunctivitis

Background. Infectious keratoconjunctivitis (IKC) is a multifactorial ocular disease affecting domestic and wild ruminants. Mycoplasma , Chlamydia and Moraxella spp. have been associated with ocular disease in various ruminant species, but their occurrence and potential role in IKC in European bison ( Bison bonasus ) remain poorly understood. This study aimed to determine the occurrence of Mycoplasma spp., Chlamydia spp., Moraxella bovoculi and Moraxella bovis in ocular samples from European bison and to assess their association with the occurrence and severity of ocular lesions. Results. Ocular samples were collected from 55 European bison in Poland between 2023 and 2025 and examined using real-time PCR. At least one of the investigated bacterial pathogens was detected in 26/55 (47.3%) bison. Mycoplasma spp. and M. bovoculi were each detected in 13/55 (23.6%) animals, while Chlamydia spp. was detected in 3/55 (5.5%); M. bovis was not detected. Ocular lesions were observed in 42/55 (76.4%) bison. Neither the occurrence nor severity of ocular lesions was significantly associated with the detection of the examined bacteria. Histopathologically, conjunctival lesions were characterized predominantly by mononuclear inflammatory infiltrates, while corneal lesions were generally mild and mainly involved stromal edema and epithelial and endothelial alterations. Conclusions. Mycoplasma spp., M. bovoculi and Chlamydia spp. were detected in ocular samples from European bison, with Mycoplasma spp. and M. bovoculi being the most frequently detected pathogens. However, their presence was not significantly associated with the occurrence or severity of ocular lesions. These findings indicate that the investigated bacteria may be components of the complex ocular microbiological landscape in European bison, but their specific contribution to the pathogenesis of IKC remains unclear and warrants further investigation.