(Coxiella burnetii infection)
Q fever is a worldwide zoonotic disease caused by the bacteria Coxiella burnetii. Although a variety of animals may be infected, cattle, sheep, and goats are the primary reservoirs for C. burnetii. Infected animals can shed the organism in birthing fluids, placenta, milk, urine, and feces. Coxiella is extremely hardy and resistant to heat, drying, and many common disinfectants, which enables it to survive for long periods in a contaminated environment (maternity pen, stall, barnyard). Infection of humans usually occurs by inhalation of C burnetii from air that contains barnyard dust contaminated by dried placental material, birth fluids, and excreta of infected animals. Other less common modes of transmission include ingestion of unpasteurized milk and dairy products, and tick bites.
The majority of infected humans exhibit mild flu-like symptoms or are asymptomatic. Acute and chronic clinical disease forms can occur in patients. Acute illness symptoms range from fever, headache, myalgia, non-productive cough, and gastrointestinal upset to more serious illness such as pneumonia, hepatitis, miscarriage, or myocarditis. Chronic Q fever is a severe illness occurring in less than 5% of infected patients. Endocarditis is the most common manifestation of the chronic form. Diagnosis of Q fever can be challenging, but the disease is often successfully treated when identified early.