Only about one-half of all people infected with Coxiella Burnetii show signs of clinical illness.  Most acute cases of Q fever begin with sudden onset of one or more of the following: high fevers (up to 104-105° F), severe headache, general malaise, myalgia, confusion, sore throat, chills, sweats, non-productive cough, nausea, vomiting, diarrhea, abdominal pain, and chest pain.  A serious complication of chronic Q fever is endocarditis, generally involving the aortic heart valves, less commonly the mitral valve.                                          Q fever is a zoonotic disease caused by Coxiella burnetii, a species of bacteria that is distributed globally.  In 1999, Q fever became a notifiable disease in the United States but reporting is not required in many other countries. Because the disease is underreported, scientists cannot reliably assess how many cases of Q fever have actually occurred worldwide.  Many human infections are inapparent.                                                                      Cattle, sheep, and goats are the primary reservoirs of C. burnetii.  Infection has been noted in a wide variety of other animals, including other species of livestock and in domesticated pets.  Coxiella burnetii does not usually cause clinical disease in these animals, although abortion in goats and sheep has been linked to C. burnetii infection.  Organisms are excreted in milk, urine, and feces of infected animals. Most importantly, during birthing the organisms are shed in high numbers within the amniotic fluids and the placenta.  The organisms are resistant to heat, drying, and many common disinfectants.  These features enable the bacteria to survive for long periods in the environment.  Infection of humans usually occurs by inhalation of these organisms from air that contains airborne barnyard dust contaminated by dried placental material, birth fluids, and excreta of infected herd animals.  Humans are often very susceptible to the disease, and very few organisms may be required to cause infection.                                                                       Ingestion of contaminated milk, followed by regurgitation and inspiration of the contaminated food, is a less common mode of transmission.  Other modes of transmission to humans, including tick bites and human to human transmission, are rare. [ Back ]