Avian chlamydiosis (or avian psittacosis) is a zoonotic disease of birds caused by the bacterium Chlamydophila psittaci. Most birds are able to spread this illness, but the most common birds that can pass this disease include parrot-type birds, especially cockatiels and budgerigars (commonly called parakeets or budgies). This bacteria can also occur in poultry, pigeons, doves, canaries, and finches.
This illness can spread between birds through breathing in infectious dust or airborne particles (such as feathers) or ingestion of material infected with the bacteria. Large quantities of this bacteria can be found in feces and can spread in the air when feces is dry.
Birds can transmit avian chlamydiosis to people causing human psittacosis. The spread of this illness to people occurs when a person breathes in dust or other dried secretions from birds. Illnesses caused by C. psittaci can result in pneumonia and other health problems in people.