The prevalence and genetic characterization of Chlamydia psittaci from domestic and feral pigeons in Poland and the correlation between infection rate and incidence of pigeon circovirus

Chlamydiosis is a zoonotic disease caused by Chlamydia psittaci that occurs in a wide range of bird species. High infection rates with C. psittaci are found in pigeons, which can act as vectors transmitting this bacterium to poultry and humans. Chlamydia shedding by pigeons is intermittent and can be activated by stressors or immunosuppression. The most common immunosuppressive factor for pigeons is a pigeon circovirus (PiCV) infection. The main aim of the study was to evaluate the prevalence of C. psittaci in Polish populations of domestic and feral pigeons (Columba livia) in the context of its correlation with PiCV infections. The second objective was to determine the genetic characteristics of Polish C. psittaci isolates. The study was conducted on 377 pigeon samples (276 domestic and 101 feral pigeons) collected from pigeons from different regions of Poland. The average prevalence of C. psittaci in the Polish pigeon population was determined at 6.8%, and it was higher in domestic than in feral pigeons. This is the first ever study to suggest a potential correlation between C. psittaci and PiCV infections, which could be attributed to the fact that there are 2 to 3 times more pigeons infected with C. psittaci and coinfected with PiCV than pigeons infected with C. psittaci alone. This trend was observed mainly in the population of sick pigeons. As many as 88.2% of isolates were recognized as belonging to genotype B, and the remaining isolates were identified as belonging to genotype E. The isolates analyzed in this study demonstrated low levels of genetic variation (96–100% homology among the isolates and in relation to reference strains). Chlamydia psittaci could be expected to spread across pigeon populations due to the high probability of mutual infections between birds and the increasing number of PiCV infections.