Avian chlamydiosis.

Avian chlamydiosis (AC) can be economically devastating to producers and a serious public health problem. Most infections in humans are due to exposure to psittacine birds and pigeons; however, outbreaks resulting in severe disease and even death do occur in abattoir workers following processing of infected flocks. The disease occurs primarily in turkeys and ducks, but can affect all types of poultry. In poultry, the disease varies from one producing high morbidity and mortality to one that is asymptomatic. Farm workers and abattoir workers are at risk following exposure to either extreme. Although outbreaks of AC have declined since the 1970s, some parts of the world are now experiencing a rise in incidence. Whether the initial decrease was due to changes in production methods or to the increased use of antibiotics is not known. The mechanism for introduction of the disease into a flock or area is poorly understood. Wild birds are often infected by the same strains as domestic flocks and are therefore thought to play a major role in introduction. Data also indicate that vertical transmission may occur. Persistently infected carrier birds are known to be a source of chlamydiosis in the pet bird industry, but have not been confirmed as a source of infection in poultry flocks.