Q fever

Q fever, acute self-limited systemic disease caused by the rickettsia Coxiella burnetii. Q fever spreads rapidly in cows, sheep, and goats, and in humans it tends to occur in localized outbreaks. The clinical symptoms are those of fever, chills, severe headache, and pneumonia. The disease is usually mild, and complications are rare. Treatment with tetracycline or chloramphenicol shortens the duration of illness.

History

Q fever was first recognized in 1935 in Queensland, Australia, by Edward Holbrook Derrick. According to Derrick, Q stands for query, an appellation applied because of the many unanswered questions posed by the new disease at the time of its first description. The disease was originally encountered among abattoir workers, cattle ranchers, and dairy farmers in Australia and later among sheep ranchers, and it was at first thought to be restricted to that continent. However, several outbreaks of what was ultimately shown to be Q fever occurred among Axis and Allied troops in the eastern Mediterranean theatre of World War II during the winter of 1944–45. These were the first naturally occurring outbreaks of Q fever recognized outside Australia, and the disease thereafter was reported from various parts of the world.

Transmission

Q fever is transmitted primarily through the inhalation of dust contaminated with particles of urine, feces, and placenta and birth fluids from animals that are infected with C. burnetii. Contamination of the environment leads to airborne dissemination of the rickettsiae and thus to infection of persons in close contact with livestock, contaminated clothing, and other infected sources. Because the infectious organism also is found in the milk of infected animals such as cows and goats, the ingestion of contaminated dairy products can result in infection of humans and livestock. Less commonly, the organism may be transmitted via blood transfusion, in humans, or by the bite of an infected tick, in humans and livestock.

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Symptoms and treatment

The incubation period of the disease is two to four weeks, averaging about 18 to 21 days. The onset may be gradual but generally is sudden, and the disease is ushered in by fever, chills or chilly sensations, headache, muscle aches, loss of appetite, disorientation, and profuse sweating. Symptoms in the upper respiratory tract may be present but generally are infrequent and minimal; pneumonia, even when relatively extensive, may be detectable only by X-ray examination. Although Q fever is, on the whole, a mild disease, it can sometimes result in severe and protracted illness. The outlook for recovery is excellent; the mortality rate is believed to be less than 1 percent. The disease is amenable to therapy with wide-spectrum antibiotics, particularly doxycycline, which is highly effective.

Q fever seems to be in large part an infection associated with particular occupations; for example, individuals who work with animals, such as veterinarians, and those who work in slaughterhouses are at increased risk of infection. In some places, such as Australia, a vaccine prepared from killed C. burnetii is available and can be used to protect persons whose work makes them likely to be exposed to infection. The disease can also be prevented by avoiding the consumption of raw milk and by avoiding contact with animals that may be infected.