Human psittacosis (ornithosis) is a zoonotic pneumonia contracted through inhalation of respiratory secretions or dust from droppings of infected birds. It was initially described in psittacines, such as parrots and parakeets, but was subsequently shown to occur in a wide range of avian species, including turkeys. Human infections have also been linked to livestock and cat reservoirs. The disease is usually latent in its natural host but may be-come active, particularly with the stress of recent captivity or transport; C. psittaci is then excreted in large amounts.
Psittacosis in humans is seen mainly as an occupational hazard of poultry workers and bird fanciers, particularly owners of psittacine birds. Reported cases of human psittacosis in the United States decreased during the 1950s, in association with the use of antimicro-bials in poultry feeds and quarantine regulations for imported psittacine birds. Currently 100 to 200 cases are reported each year. Some strains of C. psittaci are highly contagious and pose a hazard for laboratory workers processing specimens for C. psittaci isolation.
Psittacosis in humans is an acute infection of the lower respiratory tract, usually present-ing with acute onset of fever, headache, malaise, muscle aches, dry hacking cough, and bilateral interstitial pneumonia. Occasionally, systemic complications such as myocardi-tis, encephalitis, endocarditis, and hepatitis may develop. The liver and spleen are often enlarged. The diagnosis of psittacosis should be suspected in any patient with acute onset of febrile lower respiratory illness who gives a history of close exposure to birds. Indeed, a history of bird exposure should be especially sought in patients who appear to have a bi-lateral pneumonia not proven to be caused by other agents. It must be remembered that spread can occur from both symptomatic and asymptomatic infections of birds. The spe-cific diagnosis is usually made by demonstrating seroconversion, or a fourfold rise in the titer of complement-fixing or indirect fluorescent antibody to chlamydial group antigen. Although C. psittaci can be isolated from blood or sputum early in the disease, these methods are attempted only in specialized laboratories because of the risk of laboratory infection. Treatment with tetracycline or erythromycin is effective if given early in the course of illness.