In medicine (pulmonology), psittacosis -- also known as parrot disease, parrot fever, and ornithosis -- is a zoonotic infectious disease caused by a bacterium called Chlamydophila psittaci (formerly Chlamydia psittaci) and contracted not only from parrots, macaws, cockatiels and parakeets, but also from pigeons, sparrows, ducks, hens, sea gulls etc. The incidence of infection in canaries and finches is believed to be lower than in psittacine birds.

In birds

In birds, Chlamydophila psittaci infection is referred to as avian chlamydiosis (AC). Infected birds shed the bacteria through feces and nasal discharges, which can remain infectious for several months.

In humans

Symptoms

In humans, after incubation period of 5-14 days, the symptoms of the disease range from inapparent illness to systemic illness with severe pneumonia. It presents chiefly as an atypical pneumonia with influenza-like symptoms like fever, chills, headache, muscle aches, and a dry cough. Pneumonia can be often visualized on a chest X-ray.

Complications in the form of endocarditis, hepatitis, myocarditis, arthritis, keratoconjunctivitis, and neurologic complications (encephalitis) may occasionally occur. Severe pneumonia requiring intensive-care support may also occur. Fatal cases have been reported (less than 1% of cases).

Diagnosis

Diagnosis involves microbiological cultures from respiratory secretions of patients or serologically with a fourfold or greater increase in antibody titers against C. psittaci in blood samples combined with the probable course of the disease.

Epidemiology

Since 1996, fewer than 50 confirmed cases were reported in the United States each year. Many more cases may occur that are not correctly diagnosed or reported.

Bird owners, pet shop employees, and veterinarians are at risk of the infection. Some outbreaks of psittacosis in poultry processing plants have been reported.

Treatment

The infection is treated with antibiotics. Tetracyclines are the drugs of choice for treating patients with psittacosis. Most persons respond to oral therapy (100 mg of doxycycline administered twice a day or 500 mg of tetracycline hydrochloride administered four times a day). For initial treatment of severely ill patients, doxycycline hyclate may be administered intravenously at a dosage of 4.4 mg/kg (2 mg/lb) body weight per day divided into two infusions per day (up to 100 mg per dose). In past years, tetracycline hydrochloride has been administered to patients intravenously (10-15 mg/kg body weight per day divided into four doses per day). Remission of symptoms usually is evident within 48-72 hours. However, relapse can occur, and treatment must continue for at least 10-14 days after fever abates. Although its in vivo efficacy has not been determined, erythromycin probably is the best alternative agent for persons for whom tetracycline is contraindicated (e.g., children aged less than 9 years and pregnant women).