Host preference and zoonotic potential of Chlamydia psittaci and C. gallinacea in poultry

Chlamydia psittaci and C. gallinacea are obligate intracellular bacteria infecting poultry. We conducted a survey in two poultry slaughterhouses that were processing either exclusively ducks (A) or various poultry species except ducks (B). Cloacal swabs were collected from all incoming poultry flocks in the course of a week, and blood samples and pharyngeal swabs were taken from workers. Swabs were examined using PCR and sera were analyzed with two immunoassays. PCR testing revealed the presence of C. psittaci in 9/38 duck flocks and the complete absence of C. gallinacea in these flocks (slaughterhouse A), whereas 16/33 Chlamydiaceae-positive poultry flocks handled in slaughterhouse B harbored C. gallinacea only. In an episode of psittacosis in slaughterhouse A, where one PCR-positive worker presented clinical signs, seroconversions were detected in 10 workers. In contrast, serological responses of slaughterhouse B workers to C. psittaci were generally low. This is in line with the almost complete absence of C. psittaci in handled flocks, where in additional sampling campaigns the agent was detected only once in the course of a year. Our study indicates that C. psittaci has a certain preference for ducks, whereas C. gallinacea was the predominant chlamydial agent in chickens and guinea fowl flocks.