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Avian Chlamydiosis

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

Avian chlamydiosis (AC) is a zoonotic disease caused by the bacterium Chlamydia, which occurs commonly in domestic and wild birds worldwide. The disease can develop in acute, subacute, or chronic form, depending on the virulence of the strain, infectious dose, immune status, and age of the bird.

Clinical Signs

Clinical signs of avian chlamydiosis in chickens are generally nonspecific and vary greatly in severity, depending on the age of the bird, immune status, and strain of the bacteria. Some birds may be infected and show no signs of disease. The most common clinical signs observed in chickens include reduced appetite, 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.


Chlamydia is transmitted between birds primarily through inhalation of contaminated fecal or feather dust. Exotic and wild birds are frequent carriers and act as reservoirs. Both diseased and subclinically infected birds can shed Chlamydia in their feces.

Incubation period

The incubation period of Chlamydia infection ranges from 3 days to several weeks.


Avian chlamydiosis can be confirmed via Chlamydia PCR tests offered at several veterinary diagnostic laboratories. Usual specimens required include one of the following: nasopharyngeal swab, conjunctival swab, cloacal swab, feces, or if post mortem, lung, liver or spleen.

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.

Gross lesions usually include splenic and hepatic enlargement, with pulmonary congestion. Necrotizing splenitis, hepatitis, interstitial pneumonia and nephritis may be seen histologically.


Avian chlamydiosis is treated with antibiotics. Doxycycline is the drug of choice, and usually requires long-term treatment to be effective. Calcium should not be added to the diet during treatment, since it interferes with the effectiveness of the drug.

Clinical Signs

Greenish diarrhea
Ruffled feathers
Nasal/ocular discharge
Poor appetite
Weight loss


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

Reported Cases

  • Case 1: Chlamydiosis in a Finch In May 2018, avian chlamydiosis was diagnosed in a 1-year-old male Gouldian finch at the Turlock Branch of the California Animal Health and Food Safety Laboratory System. The bird belonged to an outdoor aviary with mixed avian species, including Gouldian finches, doves, and psittacines. Severe respiratory distress and mortality were noted among the finches. Gross and histopathologic lesions were concentrated in the liver and spleen, with a mild involvement of the upper respiratory tract. Chlamydia spp. were detected in the spleen and kidney by real-time PCR and were further confirmed by immunohistochemistry. Subsequently, Chlamydia psittaci was isolated from the liver and spleen and characterized as a CP3-like strain (genotype B). In addition, viral particles compatible with circovirus were identified in the liver by direct electron microscopy. Ref

  • Case 2: Avian chlamydiosis in a Parrot A two-year-old Congo African grey parrot was examined since the bird had shown clinical signs of anorexia, depression, diarrhea, and mild dyspnea and based on biochemical and hemathological analysis the bird was diagnosed as having anemia, leukocytosis, heterophilia, lymphopenia and monocytosis. With regards to clinical and paraclinical findings, the case was diagnosed to be carrying Chlamydiophila spp. In addition, choanal cleft and cloaca swabs were positive for Chlamydiophila spp. in a diagnostic polymerase chain reaction (PCR) (600 bp amplicon). Polymerase chain reaction products were typed by ompA gene-based PCR, using CTU/CTL primers (1050 bp amplicon). The PCR product sequence was compared with the sequences obtained from GenBank. The phylogenetic tree has revealed 100% identity with genotype B obtained from previous studies. The bird was hospitalized and treated with doxycycline regimen for 45 days, with a weekly sampling process to trace the presence of C. psittaci DNA in faecal and choanal swabs, this process continued to the point where the specimens turned negative after two weeks. Laboratory and radiology results were within normal limits after the treatment. Genotype B is predominantly isolated from Columbidae and there have not been any reports regarding the clinically affected African gray parrot with this genotype. Ref

  • Case 3: Avian chlamydiosis in a Turkeys Chlamydiosis affecting only the nasal glands was observed in less than 1% of 24-week old turkey hens in a flock of 5,000 birds. The disease was clinically manifested by mild to moderate swelling above the eyes and was diagnosed based on FAT, PCR and immunohistochemistry. They killed the birds to prevent it from spreading. Ref

  • Case 4: Avian chlamydiosis in a Turkeys Ornithosis caused swelling over the eyes in 13-week-old, female turkeys. Ten percent of 36,000 birds were affected. Histologically, there was nasal gland inflammation and chlamydia was detected only in the nasal gland by immunohistochemistry and fluorescent antibody (FA) testing. The birds were otherwise healthy. Testing of wild pigeons on a neighboring farm confirmed the presence of chlamydia by FA. Ref

  • Case 5: Avian chlamydiosis in a Penguin An outbreak of Chlamydophila psittaci occurred in an outdoor colony of 63 Magellanic penguins at the San Francisco Zoo. Affected penguins presented with inappetence, lethargy, and light green urates. Hematologic and serum biochemical findings were consistent with chronic inflammation. Penguins did not respond to initial supportive and antimicrobial therapy, and 3 died. Necropsy results of the 3 birds revealed hepatomegaly and splenomegaly, and histologic lesions included necrotizing hepatitis, splenitis, and vasculitis. Chlamydophila psittaci infection was confirmed by results of Gimenez staining, immunohistochemistry, and tissue polymerase chain reaction assay. As additional birds continued to present with similar clinical signs, the entire colony of penguins was prophylactically treated with a 30-day minimum course of doxycycline, administered orally or intramuscularly or as a combination of both. Despite treatment, 9 additional penguins died during a 3-month period. Pathologic results from these birds revealed renal and visceral gout (n = 4), cardiac insufficiency (n = 2), sepsis from a suspected esophageal perforation (n = 2), and no gross lesions (n = 1). During the outbreak, 4 birds presented with seizures, 5 developed dermatitis, and nearly 90% of birds in the colony showed severe keratoconjunctivitis, believed to be related to drug therapy with doxycycline. We report the clinical and pathologic features of Chlamydophila psittaci infection in an outdoor colony of penguins and the associated challenges of treatment. Ref

  • Case 6: Conjunctivitis and rhinitis in a Duck Chlamydia psittaci was isolated from the eyes of domestic ducks with conjunctivitis and rhinitis. Ref


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.
DoxycyclineVibramycin 25 mg/kg PO q12h for 45 days or Vibravenos 50-100 mg/kg IM q7d for 6 injections.
OxytetracyclineLA-200 50 mg/kg IM q24h x 5-7 days (if doxycycline is unavailable).
Flurbiprofen ophthalmic dropsTo help reduce pain and inflammation, if eyes are affected.
Artificial tearsTo help maintain moisture of the eyes.



  • Don't let exotic pet birds (parrots) live in the same environment as chickens.
  • Prevent exposure to wild birds.
  • Isolate and quarantine newly acquired birds for a minimum of 6 weeks.
  • Minimize stress

Scientific References

Good Overviews

Risk Factors

  • Exposure to psittacines and columbiformes (pet parrots, pigeons and doves).
  • Exposure to wild birds.
  • Close contact with infected birds that are shedding the organism.
  • Stressed birds, since they have a greater tendency to shed the organism during times of stress.