Avian Chlamydiosis

Key Points

  • Avian chlamydiosis is caused by Chlamydophila psittaci, an obligate intracellular bacterium.
  • Chlamydophila psittaci may be excreted in feces or oculonasal discharge.
  • Clinical signs may include lethargy, anorexia, ruffled feathers, oculonasal discharge, diarrhea, yellow-green urates or biliverdinuria, anorexia, emaciation, dehydration, and death.
  • Latent infections may occur in which birds may shed the organism intermittently for months to years.
  • Definitive diagnosis relies on culture, identification of antigen by immunofluorescence, a ≥ 4-fold rise in titer, or identification of the organism using stained smears.
  • More commonly, clinicians identify probable cases of psittacosis, which are defined as compatible clinical signs and a single high serologic titer or detection of Chlamydiaceae antigen using ELISA, PCR, or immunofluorescence.
  • Isolate and treat all birds with confirmed or probable psittacosis for 45 days. The drug of choice for avian chlamydiosis is doxycycline.
  • Most human cases of psittacosis result from exposure to infected psittacines, and all new bird owners should be advised on the risks of Chlamydophila infection.


Psittacosis or ornithosis is caused by Chlamydophila psittaci, an obligate intracellular bacterial infection of birds. Chlamydophila psittaci may be excreted in feces and oculonasal discharge. Chlamydophila is environmentally labile but remains infectious for months in organic debris. Latently infected birds appear healthy but shed the organism intermittently for months to years. Stressors such as breeding, shipping, crowding, or climatic extremes may activate shedding.

Clinical disease

Incubation ranges from 3 days to several weeks, however, a latently infected bird can present with active disease after no identifiable exposure. Whether the bird has acute or chronic illness depends on the species and age of the bird, virulence of the strain, infectious dose, stress factors, and extent of treatment. Clinical signs include lethargy, anorexia, ruffled feathers, oculonasal discharge, diarrhea, yellow-green urates or biliverdinuria, emaciation, dehydration, and death.


Confirmation of disease relies on at least one of four laboratory results including: isolation of C. psittaci, identification of antigen by immunofluorescence of tissues, a ≥ 4-fold change in serologic titer in 2 samples at least 2 weeks apart, or identification of Chlamydiaceae within macrophages in Gimenez or Macchiavello stained smears.

A probable case of psittacosis is defined as compatible illness and at least one of two positive results, including a single high serologic titer obtained after the onset of signs or detection of Chlamydiaceae antigen (identified by ELISA, PCR, or fluorescent antibody) in feces, respiratory or ocular exudates, or a cloacal swab.

Care of infected birds

All birds with confirmed or probable avian chlamydophilosis should be isolated and treated. Treatment of avian chlamydiosis can be challenging. The drug of choice for avian chlamydiosis is doxycycline. As treated birds can be re-infected, they should not be exposed to untreated birds or other potential sources of infection. To prevent re-infection, contaminated aviaries should be thoroughly cleaned and disinfected several days before treatment ends.

While birds are under treatment, outpatient care should include:

  • Minimize stress by improving husbandry and nutrition. House birds in clean, un-crowded cages. Wash dishes daily, and provide fresh water and appropriate vitamins daily.
  • Weigh birds regularly (every 3 to 7 days). If the birds are not maintaining weight, they should be re-evaluated by a veterinarian.
  • Avoid high dietary concentrations of calcium and other divalent cations because they inhibit the absorption of tetracyclines. Remove oyster shell, grit, mineral blocks, and cuttlebone.
  • Continue medication for the full treatment period (45 days) to avoid relapses. Birds can improve clinically and have reduced chlamydial shedding after 1 week.

Controlling infection in humans and birds

To prevent transmission of C. psittaci to humans and birds, specific control measures are recommended:

  • Educate persons at risk. Individuals working and living with birds should be made aware of the high natural incidence of psittacosis, especially in birds of low economic value that may not be tested such as parakeets and cockatiels.
  • Instruct at-risk personnel to wear protective clothing, gloves, a disposable surgical cap, and an appropriately fitted respirator with N95 or higher rating when cleaning cages or handling infected birds. Surgical masks may not be effective in preventing transmission of C. psittaci.
  • When necropsies are performed on potentially infected birds, wet carcasses with detergent and water to prevent aerosolization of infectious particles. Perform the procedure within a biological safety cabinet or equivalent.
  • Pet stores should maintain detailed records of all bird-related transactions for at least 1 year to aid in identifying sources of infected birds and potentially exposed persons.
  • Avoid purchasing or selling birds that appear ill.
  • Quarantine newly acquired, ill, or exposed birds. Isolate birds that have left and returned to the site, or who are new to the site (including those who have been to the vet office, shows, exhibitions, fairs, and other events) for at least 30 days. Isolation should include housing in a separate air space from other birds.
  • Test or prophylactically treat quarantined birds before adding them to a group. Veterinarians should also test birds of unknown health status (i.e. not previously tested, or exposed since last test), in particular prior to hospitalization, in view of the risk of zoonotic or cross infection to other patients. Owners should be advised not to mix tested birds with birds of unknown health status.
  • Isolate birds requiring treatment. Rooms and cages where infected birds were housed should be cleaned immediately and disinfected thoroughly.
  • Practice preventive husbandry. Position cages to prevent the transfer of feces, feathers, food, and other materials from one cage to another. Wherever possible keep untested or unhealthy birds isolated in separate air space, so that cross contamination cannot occur.
  • Remove organic debris thoroughly before disinfection. Chlamyodphila psittaci is susceptible to most disinfectants and detergents as well as heat. Remember many disinfectants are respiratory irritants and should be used in a well-ventilated area.

Zoonotic potential

Human infection with Chlamydophila psittaci or psittacosis results from exposure to infected psittacines, and all new bird owners should be advised about the risks of Chlamydophila infection. Human infection is called ornithosis when caused by non-psittacines. Apart from exposure to infected pet birds, individuals at risk include pigeon fanciers, employees in poultry slaughtering and processing plants, veterinarians and technicians, zoo, laboratory and avian quarantine employees, farmers, gamekeepers, and wildlife rehabilitators. Humans can be infected during transient exposure to infected birds and contact may be so brief the patient may forget. Person-to-person transmission has been suggested but not proven.

An average 250 human cases of Chlamydophila psittaci are reported annually in the United States. Clinical signs typically follows a 5 to 14 day incubation period. Disease ranges from sub-clinical to systemic illness with severe pneumonia. Most people demonstrate sudden onset fever, headache, malaise, and myalgia with a non-productive cough that can be accompanied by breathing difficulty and chest tightness. Splenomegaly and a non-specific rash are also sometimes observed. Chlamydophila can also cause endocarditis, myocarditis, hepatitis, arthritis, keratoconjunctivitis, and encephalitis. Respiratory failure, thrombocytopenia, hepatitis, and fetal death have been reported in pregnant women. Disease is fatal in less than 1% of properly treated humans, however fatality can reach 15 to 20% where antimicrobials are not provided.

In the event a bird tests positive, provide a client education handout detailing clinical signs in birds and humans and actions to be taken by concerned humans. First and foremost, humans exposed to birds with chlamydophilosis should seek medical attention if they develop flu-like symptoms or respiratory problems. Physicians should consider psittacosis in all ill patients exposed to birds, and early, specific treatment for psittacosis should be initiated. Most states require physicians to report psittacosis cases to public health authorities. Timely diagnosis and reporting can help identify the source of infection and control the spread of disease.

Animal and public health authorities may issue quarantine for all birds on premises where C. psittaci infection has been identified. With the approval of state or local authorities, bird owners may choose to:

  1. Treat birds in a separate quarantine area
  2. Sell birds that have completed at least 7 days of treatment, provided the new owner agrees in writing to continue quarantine and treatment and is informed of the disease hazards, or
  3. Euthanize infected birds

After completion of treatment or removal of birds, quarantine can be lifted after infected premises are thoroughly cleaned and disinfected. The area can then be restocked with birds.

For more information, see the Compendium of Measures to Control Chlamydophila psittaci (formerly Chlamydia psittaci) Infection Among Humans (Psittacosis) and Pet Birds, 2005.



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To cite this page:

Forbes N. Avian chlamydiosis. January 29, 2008. LafeberVet Web site. Available at https://lafeber.com/vet/avian-chlamydiosis/