Coxiella burnetii, the infectious agent of Q fever, courtesy U.S. Dept. of Health
Q fever is an infectious bacterial disease caused by the bacteria coxiella burnetii. The bacteria is one of the most virulent known and even a single bacteria can lead to symptoms. Although the bacteria is rare in the wild, it can be found anywhere there are domestic animals. Although it can be transmitted by airborne spores, it can also be contracted from the milk, semen, feces or urine of an infected animal. The bacteria is very hardy and can survive for long periods of time in the environment. Although it was first identified as a separate disease in Australia in the early 20th century when there was an outbreak among slaughterhouse workers, the bacteria wasn't identified until 1937. It is now known that the bacteria can be found worldwide except for New Zealand.
Q fever presents with symptoms similar to the flu, and cases often resolve themselves in about two weeks. However, the disease can progress to pneumonia, endocarditis or cause liver inflammation, in which case the mortality rate can be very high.
People who work regularly with animals are at higher risk, including veterinarians, stockyard workers, farmers, shearers, and tannery workers.
Q fever's symptoms are very similar to many other infections and, because of its rarity (about 300 cases a year in the United States), it is very much a zebra diagnosis. A definitive diagnosis can usually only be obtained by testing to see if the patient has antibodies to the disease.
Luckily, Q fever responds very well to most antibiotics. However, it is often difficult to treat pregnant women because the most common antibiotics used to treat the disease are contra-indicated in pregnant women due to risk of birth defects. There is also a vaccine for Q fever which is recommended for individuals in high risk occupations.