Symptoms in humans
The incubation period is 9 to 40 days. About half of the infections are asymptomatic or mild. However, flu-like symptoms can also occur, such as sudden onset of fever, chills, fatigue, headache, aching limbs, cough, chest pain, and rarely gastrointestinal symptoms. The fever, which is usually mild, lasts for about seven to fourteen days.
Occasionally, there are severe acute courses with pneumonia or liver inflammation. Rarely, the disease can become chronic, for example as Q fever endocarditis (inflammation of the heart valves). Pregnant women and people with pre-existing conditions (e.g. immunosuppressed persons and people with artificial heart valves or vascular prostheses) are particularly at risk.
Symptoms in animals
In cattle and sheep, Q fever usually runs its course without clear symptoms. If it does, the infection is manifested by a reluctance to eat, miscarriages, malformations, udder inflammation and infertility.