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Avian Chlamydiosis

Other Names: Chlamydiosis, Parrot Fever, Psittacosis, Chlamydia, Ornithosis

Avian chlamydiosis (AC) is a zoonotic disease (meaning humans can become infected as well) caused by the bacterium Chlamydia psittaci. The disease is often associated with exposure to wild or pet psittacine birds (parrots, parakeets, macaws, and cockatiels), since they are historically known to be frequent carriers. Avian chlamydiosis can develop in acute, subacute, or chronic form, depending on the virulence of the strain, infectious dose, stress factors, age, and extent of treatment or prophylaxis.

Clinical signs of avian chlamydiosis in chickens are often nonspecific and include lethargy, reduced appetite, and ruffled feathers. Other signs include serous or mucopurulent discharge from the eyes or nares, conjunctivitis, diarrhea, and excretion of green to yellow-green urates in feces. When birds are severely affected, they may produce sparse, dark green droppings, followed by emaciation and dehydration, leading to death.

How Avian Chlamydiosis is Transmitted to Chickens

C. psittaci is transmitted by inhalation of desiccated droppings and secretions, both ocular and nasal, from infected birds, or through ingestion of contaminated feces. Exotic and wild birds are frequent carriers and act as reservoirs. Both diseased and sub-clinically infected birds can shed C. psittaci.

The incubation period of C. psittaci ranges from 3 days to several weeks.

How Avian chlamydiosis is Diagnosed

Avian chlamydiosis can be confirmed using a variety of available tests offered at veterinary diagnostic laboratories. Bloodwork typically shows an elevated WBC with a heterophilia/lymphopenia with toxic changes. The total protein is elevated with increases in the beta- and gamma-globulins. Post-mortem lesions seen include splenic and hepatic enlargement, with pulmonary congestion. Necrotizing splenitis, hepatitis, interstitial pneumonia and nephritis may be seen histologically. The organism can be confirmed using a C. psittaci PCR (DNA) probe and tissues, or by culture.

Treatment for Avian Chlamydiosis in Chickens

Doxycycline is the drug of choice. However, Oxytetracycline can also be used if Doxycycline is not available.

Clinical Signs

Green to yellow-green urates in feces
Ruffled feathers
Poor appetite


  • History
  • Clinical signs
  • PCR
  • Radiographs
  • Endoscopy
  • Cytology
  • Sinus flush and culture


Supportive careIsolate the bird from the flock and place in a safe, comfortable, warm location (your own chicken "intensive care unit") with easy access to water and food. Limit stress. Call your veterinarian.
DoxycyclineDrug of first choice.
OxytetracyclineIf doxycycline is not unavailable.



  • Don't let exotic pet birds (parrots) live in the same environment as chickens.
  • Prevent exposure to wild birds.

Scientific References

Good Overviews

Risk Factors

  • Exposure to psittacines and columbiformes (pet parrots, pigeons and doves).
  • Exposure to wild birds.