Prevalence, risk factors and genetic diversity of Chlamydia felis in cats.

Introduction: Chlamydia felis is the main chlamydial pathogen of cats and is associated with conjunctivitis and respiratory disease. This study aimed to estimate the prevalence of Chlamydiaceae and Chlamydia felis, to explore risk factors and predictors (age, sex, breed, origin and ocular signs) for infection using logistic regression, and to appraise genetic diversity via ompA sequencing and phylogenetic analysis. Material and Methods: Conjunctival swabs from 156 cats were examined using real-time PCR assays for Chlamydiaceae and C. felis. Logistic regression and Kaplan-Meier analysis evaluated risk factors, and partial ompA sequences were phylogenetically analysed. Results: Chlamydiaceae DNA was detected in 7.7% (12/156) of cats and was identified as C. felis. Infections were mostly unilateral. Threshold cycle values varied widely, suggesting heterogeneous bacterial loads. Younger age was a significant risk factor, and the probability of infection decreased steadily with age. Ocular signs strongly predicted infection. British Shorthair/Longhair cats had more than threefold higher odds of infection than European Shorthair cats. Phylogenetic analysis of ompA showed very high genome conservation (99.7-100%), which was consistent with global data. Conclusion: This first molecular study of C. felis in Poland in ten years demonstrates that infection mainly affects young, purebred cats with apparent conjunctivitis. The genetic stability of ompA supports the concept of a globally homogeneous C. felis population.