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Psittacosis, Chlamydophila psittaci

What is psittacosis?

Psittacosis – also known as parrot fever and ornithosis – is spread by a bacterial infection of birds that can cause severe pneumonia and other serious health problems among humans. From 1988 through 1998, 813 cases of psittacosis (infection with Chlamydophila psittaci) were reported to CDC, and most resulted from exposure to infected pet birds, usually cockatiels, parakeets, parrots, and macaws. This is an underrepresentation of the actual number of cases because psittacosis is difficult to diagnose and cases often go unreported. In birds, C. psittaci infection is referred to as avian chlamydiosis (AC). Infected birds shed the bacteria through feces and nasal discharges, and humans become infected from exposure to these materials.

Who can get psittacosis and how is it spread?

Most C. psittaci infections in humans result from exposure to pet psittacine birds. However, transmission has been documented from free-ranging birds, including doves, pigeons, birds of prey, and shore birds. Infection with C. psittaci usually occurs when a person inhales the organism, which has been aerosolized from dried feces or respiratory secretions of infected birds. Other means of exposure include mouth-to-beak contact and the handling of infected birds’ plumage and tissues. Even brief exposures can lead to symptomatic infection; therefore, some patients with psittacosis might not recall or report having any contact with birds. Other persons at risk include pigeon fanciers and persons whose occupation places them at risk for exposure (e.g., employees in poultry slaughtering and processing plants, veterinarians, veterinary technicians, laboratory workers, workers in avian quarantine stations, farmers, wildlife rehabilitators, and zoo workers). Because human infection can result from brief, passing exposure to infected birds or their contaminated droppings, persons with no identified leisure-time or occupational risk can become infected. Mammals occasionally transmit C. psittaci to humans. Certain strains of C. psittaci infect sheep, goats, and cattle, causing chronic infection of the reproductive tract, placental insufficiency, and abortion in these animals. These strains of C. psittaci are transmitted to persons when they are exposed to the birth fluids and placentas of infected animals. Another strain of C. psittaci, feline keratoconjunctivitis agent, typically causes rhinitis and conjunctivitis in cats. Transmission of this strain from cats to humans rarely occurs. Person-to-person transmission has been suggested but not proven. Standard infection-control precautions are sufficient for patients with psittacosis, and specific isolation procedures (e.g., private room, negative pressure air flow, and masks) are not indicated.

What are the clinical signs and symptoms of psittacosis in man?

The onset of illness typically follows an incubation period of 5-14 days, but longer periods have been reported. The severity of this disease ranges from inapparent illness to systemic illness with severe pneumonia. Before antimicrobial agents were available, 15%-20% of persons with C. psittaci infection died. However, <1% of properly treated patients now die as a result of the infection. Persons with symptomatic infection typically have abrupt onset of fever, chills, headache, malaise, and myalgia. They usually develop a nonproductive cough that can be accompanied by breathing difficulty and chest tightness. A pulse-temperature dissociation (fever without elevated pulse), enlarged spleen, and rash are sometimes observed and are suggestive of psittacosis in patients with community-acquired pneumonia. Auscultatory findings can underestimate the extent of pulmonary involvement. Radiographic findings include lobar or interstitial infiltrates. The differential diagnosis of psittacosis-related pneumonia includes infection with Coxiella burnetii, Mycoplasma pneumoniae, Chlamydophila pneumoniae, Legionella species, and respiratory viruses such as influenza. C. psittaci can affect organ systems other than the respiratory tract and result in endocarditis, myocarditis, hepatitis, arthritis, keratoconjunctivitis, and encephalitis. Severe illness with respiratory failure, thrombocytopenia, hepatitis, and fetal death has been reported among pregnant women.

How we can test psittacosis?

Most diagnoses are established by using serologic methods in which paired sera are tested for chlamydial antibodies by complement fixation (CF) test. However, because chlamydial CF antibody is not species-specific, high CF titers also can result from C. pneumoniae and C. trachomatis infections. Acute-phase serum specimens should be obtained as soon as possible after onset of symptoms, and convalescent-phase serum specimens should be obtained 2 weeks after onset of symptoms. Because antibiotic treatment can delay or diminish the antibody response, a third serum sample might help confirm the diagnosis. All sera should be tested simultaneously at the same laboratory. If the patient’s epidemiologic and clinical history indicate a possible diagnosis of psittacosis, microimmunofluorescence (MIF) test, enzyme-linked immunosorbent assay (ELISA), and polymerase chain reaction (PCR) can be used to distinguish C. psittaci infection from infection with other chlamydial species. MIF test is simple, very economical in the use of reagents and became a method of choice for a large number of sera to be screened. However, the data obtained are highly subjective and the results may vary considerably from laboratory to laboratory. Thus, it appears that ELISA is the most reliable serological method in diagnosing psittacosis. The infectious agent also can be isolated from the patient’s sputum, pleural fluid, or clotted blood during acute illness and before treatment with antimicrobial agents; however, culture of C. psittaci is performed by few laboratories because of technical difficulty and safety concerns. A patient is considered to have a confirmed case of psittacosis if clinical illness is compatible with psittacosis and the case is laboratory confirmed by one of three methods: a) C. psittaci is cultured from respiratory secretions; b) antibody against C. psittaci is increased by fourfold or greater (to a reciprocal titer of 32 between paired acute- and convalescent-phase serum specimens collected at least 2 weeks apart) as demonstrated by CF or MIF; or c) immunoglobulin M antibody is detected against C. psittaci by MIF (to a reciprocal titer of 16). A patient is considered to have a probable case of psittacosis if clinical illness is compatible with psittacosis and a) the patient is epidemiologically linked to a confirmed human case of psittacosis or b) a single antibody titer of 32, demonstrated by CF or MIF, is present in at least one serum specimen obtained after onset of symptoms.

What is the treatment for psittacosis?

Tetracyclines are the drugs of choice. Most patients 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 can 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). 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 in patients for whom tetracycline is contraindicated (e.g., children aged <9 years and pregnant women).
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