Chlamydia psittaci in ducks: a hidden health risk for poultry workers.

Chlamydia psittaci is a zoonotic pathogen associated primarily with avian chlamydiosis also referred as psittacosis. Human psittacosis can lead to severe cases of respiratory disease. The mule duck is one of the main bird hybrids associated with human cases of psittacosis in France. In order to better understand the epidemiology of avian chlamydiosis, monitoring studies were performed in both breeder flocks and mule duck flocks. Surveys conducted in one professional duck bredding organization revealed little shedding in breeder flocks, whereas heavy but asymptomatic C. psittaci shedding was observed in most of the mule duck flocks, mostly when birds were reared in open range conditions on farms. Human cases of psittacosis linked to duck breeder flocks and their progeny led to detection of heavy shedders in all the suspected flocks despite no birds showing clinical signs. Offspring of one of the infected female flocks was analyzed and also proved to be infected by C. psittaci. Field studies suggest that C. psittaci infections in duck farms involve horizontal and probably vertical transmission but that the environment also plays an important role in maintaining infection on farms. In the light of the widespread occurrence of C. psittaci on duck farms, it has become urgent to clearly identify sources of contamination in order to take appropriate field management measures to minimize worker exposure.