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Key Features

Essentials of Diagnosis

  • Fever, chills, and cough; headache common

  • Atypical pneumonia with slightly delayed appearance of signs of pneumonitis

  • Contact with infected psittacine bird 7–15 days previously

  • Isolation of chlamydiae or rising titer of complement-fixing antibodies

General Considerations

  • Etiologic agent is Chlamydia psittaci, a bacterium

  • Infection is acquired by inhaling dried secretions from infected psittacine birds (parrots, parakeets, pigeons, chickens, ducks, and many others), which may or may not appear ill

  • The incubation period is 6–19 days

  • Exposure history may be difficult to obtain if the patient acquired infection from an illegally imported bird

Clinical Findings

Symptoms and Signs

  • The onset is usually rapid, with fever, chills, myalgia, dry cough, and headache

  • Signs include temperature-pulse dissociation, dullness to percussion, and rales

  • Pulmonary findings may be absent early

  • Dyspnea and cyanosis may occur later

  • Culture-negative endocarditis

Differential Diagnosis

  • Other atypical pneumonia (eg, viral pneumonia, Mycoplasma pneumoniae, Chlamydophila pneumoniae)

  • Unusual presentations of typical bacterial pneumonia

  • Hypersensitivity pneumonitis

  • Other cause of culture-negative endocarditis

Diagnosis

Laboratory Tests

  • The diagnosis is usually made serologically by a rise in titer of complement-fixing antibody in convalescent versus acute serum

  • Antibodies appear during the second week

  • Antibody response may be suppressed by early chemotherapy

Imaging Studies

  • The radiographic findings are those of atypical pneumonia, which tends to be interstitial and diffuse in appearance, though consolidation can occur

  • Psittacosis is indistinguishable from other bacterial or viral pneumonias by radiography

Treatment

Medications

  • Tetracycline, 500 mg every 12 hours intravenously or orally, or doxycycline, 100 mg every 12 hours orally, for 14–21 days

  • Erythromycin, 500 mg every 6 hours orally, may also be effective

Outcome

Complications

  • Endocarditis, hepatitis, and neurologic complications may occasionally occur

  • Severe pneumonia requiring intensive care support may also occur

  • Fatal cases have been reported

Prevention

  • Traceback of infected birds to distributors and breeders often is not possible because of limited regulation of the pet bird industry

Prognosis

  • Excellent with early treatment

When to Refer

  • Early referral to an infectious disease specialist for severe disease may aid in management

When to Admit

  • Respiratory compromise

  • Rapidly deteriorating clinical course

  • Suspected or proven endocarditis

Reference

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Lagae  S,  et al. Emerging Chlamydia psittaci infections in chickens and examination of transmission to humans. J Med Microbiol. 2014 Mar;63(Pt 3):399–407.
[PubMed: 24324029]

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