Q fever, an illness that is listed on bioterrorism watch lists — along with smallpox and anthrax — has been detected at an unusually high rate of incidence this summer in Colorado, according to state health officials. The likely source is diseased livestock such as sheep or goats.
The Colorado State Health Department has confirmed 13 human cases in the state in 2005, including six in Weld County. In 2004, there were three confirmed cases throughout Colorado, said John Pape, a state health department epidemiologist.
According to the U.S. Centers for Disease Control and Prevention, Q fever, or “query” fever is a zoonotic disease caused by Coxiella burnetii, a species of bacterium 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 under-reported, scientists cannot reliably assess how many cases of Q fever have actually occurred worldwide, as 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. _C. burnetii_ does not usually cause clinical disease in these animals, although abortion in goats and sheep has been linked to infection. Organisms are excreted in milk, urine, and feces of infected animals. Most importantly, during birthing the organisms are shed in high numbers in 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 only very few organisms may be required to cause infection. Other modes of transmission to humans, including tick bites and human-to-human transmission, are rare.
Only about one-half of all people infected with C. 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 degrees F), severe headache, general malaise, myalgia, confusion, sore throat, chills, sweats, non-productive cough, nausea, vomiting, diarrhea, abdominal pain, and chest pain. Fever usually lasts for one to two weeks. Weight loss can occur and persist for some time. 30 to 50 percent of patients with a symptomatic infection will develop pneumonia. Additionally, a majority of patients have abnormal results on liver function tests and some will develop hepatitis. In general, most patients will recover to good health within several months without any treatment. Only 1 percent to 2 percent of people with acute Q fever die of the disease.
“Most people, even untreated, get better in 2 to 3 weeks,” said Dr. Daniel Mogyoros, an infectious disease specialist with Kaiser Permanente. “Most doctors go through their training and most of their career without ever seeing this disease.”
Since C. burnetii is a highly infectious agent that is rather resistant to heat and drying, it is considered relevant in bioterrorism. It can become airborne and inhaled by humans. A single C. burnetii organism may cause disease in a susceptible person. This agent could be developed for use in biological warfare and is considered a potential terrorist threat.