Q FEVER
Q (or Query) fever is a disease that is caused by the bacterium Coxiella burnetii. The bacterium is passed to humans by contact with infected animals such as sheep, cattle, and goats, which are the main reservoirs of the microorganism. The disease, which was first described in Australia in 1935, can have a short-term (acute) stage and, in some people, a much longer, chronic stage.
The bacterium that causes Q fever is a rickettsia. Other rickettsia are responsible for Rocky Mountain Spotted Fever and trench fever, as examples. Coxiella burnetti and the other rickettsia are Gram-negative organisms, which need to infect host cells in order to grow and divide. Outside of the host the bacteria can survive, but do not replicate. Q fever differs from the other rickettsial diseases in that it is caused by the inhalation of the bacteria, not by the bite of a tick.
Groups most at risk to acquire Q fever are those who are around animals. These include veterinarians, sheep, cattle and dairy farmers, and workers in processing plants.
The bacteria are excreted into the environment in the milk, urine, and feces of the animals. Also, bacteria can be present in the amniotic fluid and the placenta in the birthing process. The latter is particularly relevant, as humans tend to be near the animals during birth, and so the chances of transfer of the bacterium from animal to human are great.
In addition, the microorganisms are hardy and can endure environmental stress. The chances for human infection are also increased because of the persistence of the bacteria in the environment outside of the animal host. Coxiella burnetii are very hardy bacteria, being resistant to antibacterial compounds, and to environmental stresses such as heat and lack of moisture. When present in a dry area, such as in hay or the dust of a barnyard, the organisms can be easily inhaled.
The entry of only a few live bacteria or even one living bacterium is required to cause an infection in humans. The environmental hardiness and low number of microbes required for an infection has made Coxiella burnetii a potential agent of bioterrorism.
Of those who become infected, only about half display symptoms. When symptoms of Q fever appear, they can include the sudden development of a high fever, severe headache, nausea, vomiting, abdominal pain, and an overall feeling of illness. Pneumonia and liver damage can develop in some people. Usually the symptoms pass in several months. However, the establishment of a chronic disease can occur, and is fatal in over 60 per cent of cases. The chronic form may not develop immediately after the transient disease. In fact, cases have been documented where the lapse between the initial disease and the chromic form was several decades. The chronic disease can lead to heart valve damage.
Why some people display symptoms of infection while others do not is still not resolved. Neither are the reasons why the disease is self-limiting within a short time in some people but develops into a lengthy, debilitating, and potentially lethal disease in other people.
Coxiella burnetii has two different forms, which have differing surface chemistries. These are called phase I and phase II. The phase I form is associated more with the chronic Q fever than is phase II.
Diagnosis of Q fever is most reliably obtained by the detection of antibodies to the infecting bacterium. Following diagnosis, treatment consists of antibiotic therapy. The antibiotics that have achieved the most success are fluoroquinolone, rifampin, and trimethoprim-sulfamethoxazole. In the chronic form of Q fever, the antibiotics may need to be administered for several years. If the disease has damaged body parts, such as heart valve, then treatment may also involve the replacement of the damaged tissues.
Vaccination against Q fever is not yet a standard option. A vaccine is available in Australia and parts of Europe, but has not yet been approved in North America.
Prevention of the transmission of the bacterium to humans involves the wearing of masks when around domestic
animals and the prompt disposal of placenta and other tissues resulting from the birth process.
