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Q fever is an infectious disease caused by the bacterium Coxiella burnetii. The "Q" derives from "query" fever, its name before the true cause of the disease was discovered in 1937. Worldwide in occurrence, the etiologic agent is prevalent in sheep, cattle, and goats, and it is also found in ticks, rodents, birds, dogs, and rabbits. Infections in animals are usually inapparent, but the disease can cause spontaneous abortions in animals. Humans can be very susceptible and can contract the disease through inhalation of contaminated dust or particles from animal hides, excreta, and birthing materials.

Because C. burnetii proliferates within human white blood cells called monocytes, it is protected from part of the human immune system. A complex molecule called a lipopolysaccharide, found on the surface of the organism, further protects it from host serum defense factors. Human disease will usually present with sudden onset of headache, fever, chills, muscle soreness, and (sometimes) pneumonia. Hepatitis or endocarditis are rarer complications. Without modern detection methods, the disease is difficult to diagnose, and many human infections are probably unrecognized. It is suspected that host and microbial factors combine to determine the severity of human disease.

The antibiotic tetracycline is usually very effective in treating acute Q fever. Chronic inflammatory forms of the disease, such as Q fever endocarditis or hepatitis, require more than one year of antibiotic treatment.

Outbreaks of human Q fever are commonly reported in Asia, Australia, and parts of Europe. The disease was made reportable in the United States in 1999. Transmission from human to human is uncommon. Control of Q fever depends upon its recognition in animal populations and the culling of infected animals to prevent subsequent human exposure. A commercial vaccine, Qvax, is available in Australia.

HERB A. THOMPSON

JENNIFER MCQUISTON

(SEE ALSO: Communicable Disease Control)