Q fever is a highly contagious zoonotic disease caused by the intracellular pathogen Coxiella burnetii. Although this infection was first described in the 1930s, it is still poorly understood. Many domesticated and wild animals including mammals, birds, reptiles and arthropods can carry C. burnetii. In most cases, the infection is asymptomatic, but abortions or stillbirths can occur in ruminants. In sheep, 5-50% of the flock may be affected. Both symptomatic and asymptomatic animals shed C. burnetii in large quantities at parturition. Shedding can also occur in feces, milk and urine. These organisms persist in the environment for long periods and can be spread long distances by the wind.

Human outbreaks can result from the inhalation of aerosolized organisms. More often, sporadic cases occur in people who are occupationally exposed. These cases tend to result from exposure to parturient ruminants; however, cats, dogs, rabbits and other species have also been implicated. Although Q fever is usually asymptomatic or mild in humans, a few people develop serious disease. Pneumonia or hepatitis may occur in acute cases, and chronic infections can result in endocarditis or a wide variety of other diseases.