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Avian chlamydiosis (AC) is an infectious disease caused by infection with the bacterium Chlamydia psittaci. There are several strains of C. psittaci that cause varying degrees of disease severity in different avian species. The disease was originally called psittacosis because humans contracted it from psittacine birds (parrots, parakeets, macaws, and cockatiels).
The incubation period of C. psittaci ranges from 3 days to several weeks. Spread between birds (and to people) occurs mainly through breathing in dust containing dried saliva, feathers, mucous and droppings from infected birds. Direct contact with feathers, bird droppings and litter, saliva and mucous, and contaminated food or water can also result in disease. The organism is resistant to drying and can remain infectious for several months if protected by organic debris (e.g. litter or feces).
The disease can develop in acute, subacute, or chronic form. Clinical signs of chlamydiosis vary depending on the species of bird and the strain of C. psittaci involved. Birds may be infected without looking sick and can carry the disease for long periods. In cases where chickens develop signs, they are often nonspecific and include loss of appetite, ruffled feathers and lethargy. Other signs include mucous or pus from the nostrils and eyes, conjunctivitis, diarrhea, and excretion of green to yellow-green urates in feces.
Chickens become infected with Chlamydia spp. by inhaling aerosolized respiratory or nasal secretions or contaminated dust, soil, and bedding particles, or through ingestion of contaminated feeders, waterers, or pasture forage.
Avian chlamydiosis is treated with antibiotics, usually tetracyclines (chlortetracycline or doxycycline).