Chlamydia psittaci is a Gram-negative bacterium responsible for avian chlamydiosis, a respiratory disease in birds. Signs of infection may include elevated body temperature, conjunctivitis, and respiratory distress. The disease is also known to reduce egg production.

C. psittaci comprises both highly infectious strains and variants with lower transmission rates. Notably, birds infected with highly virulent strains can shed large quantities of the bacteria even without showing clinical signs.

Transmission occurs primarily through droppings and nasal discharges, though blood-sucking parasites—such as lice, mites, and flies—may also facilitate spread. Faecal shedding can be intermittent and is often triggered by stress or nutritional deficiencies.

Testing for Chlamydia psittaci is done by a cloacal swab or a combined ocular/choanal/cloacal swab. Additionally, avian polyomavirus and C. psittaci can be tested from the same cloacal swab.