Psittacosis (also called chlamydiosis, ornithosis, or parrot fever) is a bacterial infection caused by Chlamydia psittaci (formerly Chlamydophila psittaci). It is one of the most important diseases in avian medicine because it is common, easily missed, can be fatal if untreated, and is zoonotic — meaning it can be transmitted to humans, where it causes atypical pneumonia. Psittacosis is most frequently diagnosed in psittacine birds (parrots, cockatiels, budgies, macaws, cockatoos) but can affect virtually any bird species. Treatment requires a uniquely long antibiotic course — a minimum of 45 days of doxycycline for psittacine birds — because the organism’s intracellular life cycle makes it difficult to eradicate with shorter courses.
Overview
C. psittaci is an obligate intracellular bacterium with a unique life cycle involving two forms: the elementary body (the infectious, environmentally resistant form) and the reticulate body (the replicating form inside host cells). The organism infects respiratory epithelial cells, liver, spleen, and other organs.
Transmission occurs through:
- Inhalation of aerosolized dried feces, feather dust, or respiratory secretions from infected birds
- Direct contact with infected birds
- Ingestion of contaminated food or water
Carrier birds may shed the organism intermittently without showing clinical signs, especially during periods of stress (shipping, rehoming, overcrowding, concurrent illness). This makes psittacosis a frequent concern in pet stores, bird fairs, breeding facilities, and rescue organizations.
Symptoms
Clinical signs range from subclinical (no visible illness) to rapidly fatal, depending on the virulence of the strain, the bird’s species, age, and immune status:
- Lethargy and fluffed feathers
- Decreased appetite and weight loss
- Yellow-green or lime-green droppings (indicating liver involvement — biliverdinuria)
- Nasal discharge and sneezing
- Conjunctivitis (red, swollen eyes with discharge)
- Respiratory distress (tail bobbing, open-mouth breathing)
- Diarrhea
- Sinusitis (swelling around the eyes)
In cockatiels and budgies, psittacosis may present predominantly as conjunctivitis. In larger parrots, liver involvement with characteristic bright green droppings is more common. Young birds and stressed birds are most severely affected, and acute death can occur without preceding signs.
Diagnosis
- PCR testing — The most sensitive diagnostic method. Performed on combined choanal and cloacal swabs, or on feces. PCR detects C. psittaci DNA. A negative PCR does not completely rule out infection because shedding can be intermittent.
- Serology (antibody testing) — A rising antibody titer in paired samples (acute and convalescent, 2 to 4 weeks apart) supports active infection. A single positive titer indicates exposure but not necessarily active disease.
- Blood work — Elevated white blood cell count with heterophilia, elevated liver enzymes (AST, bile acids), and elevated total protein may be seen.
- Cytology and histopathology — Impression smears from liver or spleen (post-mortem) stained with Giemsa or modified Ziehl-Neelsen may reveal intracytoplasmic inclusions.
- Antigen detection — Point-of-care antigen tests are available but less sensitive than PCR.
Because shedding is intermittent, a single negative test does not rule out psittacosis. Testing should be repeated if clinical suspicion remains high.
Treatment & Medications
| Medication | Route | Key Notes |
|---|---|---|
| Doxycycline | Oral, injectable, or medicated water/food | First-line treatment. A minimum 45-day continuous treatment course is required for psittacine birds. Shorter courses result in treatment failure and continued shedding. Doxycycline binds to calcium — dietary calcium must be restricted during treatment (remove cuttlebone, mineral blocks, and high-calcium supplements). |
| Enrofloxacin | Oral or injectable | Second-line option when doxycycline is not tolerated. May be used in combination with doxycycline for severe cases. |
| Azithromycin | Oral | Alternative in some species. Less established in avian medicine than doxycycline. |
Treatment Considerations
- Dietary calcium restriction — Calcium chelates (binds) doxycycline and reduces absorption. Remove cuttlebone, mineral blocks, and calcium-fortified foods during the treatment period.
- Administration routes — Oral doxycycline (via syringe or medicated food) is preferred for accurate dosing. Medicated water is less reliable because water intake varies. Injectable (IM) doxycycline injections every 5 to 7 days may be used for birds that cannot be medicated orally, though injection site reactions can occur.
- Supportive care — Heat support, fluid therapy, and nutritional support for debilitated birds. Hospitalization may be needed for severely ill patients.
- Treat all exposed birds — All birds in contact with a diagnosed psittacosis case should be treated even if asymptomatic.
Zoonotic Risk
Psittacosis is a reportable disease in many jurisdictions because of its zoonotic potential:
- Human symptoms — Flu-like illness progressing to atypical pneumonia with headache, high fever, dry cough, and myalgia. Can be severe, particularly in immunocompromised, elderly, or pregnant individuals.
- Transmission to humans — Primarily through inhalation of aerosolized dried feces or respiratory secretions. Direct handling of infected birds is also a risk.
- Prevention for handlers — Wear a mask and gloves when cleaning cages of infected birds. Wet-clean surfaces rather than dry-sweeping to avoid aerosolizing material. Practice thorough hand hygiene. Inform your physician if you develop flu-like symptoms after bird contact.
Prevention
- Quarantine all new birds for a minimum of 30 days with veterinary examination and testing before introducing them to existing flocks.
- Maintain clean caging and air quality.
- Avoid overcrowding and minimize stress.
- Purchase birds from reputable sources.
- Regular veterinary wellness exams including screening for psittacosis.
Prognosis
- Treated birds — Good prognosis with a complete 45-day doxycycline course. Most birds recover fully.
- Untreated birds — Variable; mortality can be high (up to 50% or more in naïve, stressed, or young birds).
- Chronic carriers — Birds that are not fully treated may become intermittent shedders, posing a risk to other birds and humans.
Frequently Asked Questions
Why is the treatment course so long? C. psittaci has an intracellular life cycle, and the elementary bodies (the dormant, infectious form) are resistant to antibiotics. The 45-day course ensures that the organism is exposed to the antibiotic through multiple replication cycles, maximizing the chance of complete eradication.
Can my bird infect me? Yes. Psittacosis is zoonotic. Practice good hygiene: wear a mask and gloves when cleaning cages of infected birds, avoid kissing or mouth-to-beak contact, and see your physician if you develop respiratory symptoms.
My bird tested negative but I’m still suspicious. Should I retest? Yes. Because shedding is intermittent, a single negative test does not rule out psittacosis. Retest after 2 to 4 weeks, ideally during a period of stress (which may increase shedding), or treat empirically if clinical suspicion is high.
Can I stop treatment early if my bird looks better? No. Incomplete treatment is a primary cause of treatment failure and chronic carrier status. The full 45-day course must be completed even if the bird appears clinically recovered within days.
Is psittacosis a reportable disease? In many countries and US states, psittacosis is a reportable disease because of its zoonotic potential. Your veterinarian can advise on local reporting requirements.