Chlamydiosis in Backyard Chickens (<italic>Gallus gallus</italic>) in Italy.

Until recently, <italic>Chlamydia psittaci</italic> was considered to be the only etiological agent of avian chlamydiosis, but two new avian species, <italic>Chlamydia gallinacea</italic> and <italic>Chlamydia avium</italic>, have recently been described in poultry and pigeons or psittacine birds, respectively. The aim of this study was to explore the occurrence of <italic>C. psittaci</italic> and <italic>C. gallinacea</italic> in backyard chickens in Italy. Cloacal swabs were taken from 160 asymptomatic chickens reared in 16 backyard farms. Samples were tested for <italic>C. psittaci</italic> and <italic>C. gallinacea</italic> by specific real-time polymerase chain reaction assays, with 24 (15%) of the 160 chickens resulting positive for <italic>C. gallinacea</italic>. To attempt chlamydial isolation, new samples were obtained from two farms harboring a high prevalence (60% and 70%, respectively) of <italic>C. gallinacea</italic>-positive chickens. In total, eight <italic>C</italic>. <italic>gallinacea</italic> and one <italic>C. psittaci</italic> isolates were successfully recovered from 13 chickens. <italic>C. gallinacea</italic> was confirmed to be the endemic chlamydial species in chickens, with a high <italic>omp</italic>A intraspecies diversity. The presence of viable <italic>C. psittaci</italic> and <italic>C. gallinacea</italic> demonstrated by isolation from chickens in backyard farms poses a potential public health problem. [ABSTRACT FROM AUTHOR]