What is Q fever?
Q fever is an uncommon febrile, pneumonia-like illness that is most often contracted by people whose occupations bring them in contact with infected farm animals. First described as a disease among workers in a meat packing plant, the letter Q in the name of the disease derives from the word “query,” meaning “unknown origin,” although the Q probably also refers to Queensland, the Australian province in which the packing plant was located.
The tiny gram-negative bacterium Coxiella burnetii is the causative agent of Q fever. Usually classified with other obligate intracellular parasites known as Rickettsia, Coxiella is the only member of this group that does not need an arthropod vector for transmission. Ticks transmit the bacteria between animals, but most human transmission results from inhalation of dust containing bacteria from dried animal feces or urine or from the consumption of unpasteurized milk.
Workers in slaughterhouses and meat processing facilities have the highest risk, although veterinarians, textile workers handling raw wool, and others whose occupations put them in direct contact with cattle, sheep, and goats are also at risk. Transplant recipients, persons with cancer, and persons with chronic kidney disease have an increased risk of developing the more serious chronic form of the disease.
The acute form of the illness is most often characterized by the sudden onset of severe headache, high fever, chills, sweats, confusion, nausea, muscle pain, or general malaise. Pneumonia or hepatitis may develop in serious cases, and in a small percentage of infected persons, the infection will persist for many months as chronic Q fever. The majority of persons with the chronic form of the disease will develop endocarditis, a serious complication in which the bacteria establish additional sites of infection in the aortic heart valves.
Diagnosis of infection with C. burnetii requires an immunological or serological laboratory test designed to measure host antibodies to the pathogen. The indirect immunofluorescence assay (IFA) is widely used and considered the most dependable, but immunohistochemical staining of infected tissue and deoxyribonucleic acid (DNA) isolation and identification by the polymerase chain reaction (PCR) are also utilized.
Starting the patient on an immediate antibiotic regimen of doxycycline is the preferred treatment. It is typically prescribed as a dosage of 100 milligrams, twice per day, for two to three weeks. Tetracycline and hydroxychloroquine have also proven useful. Treatment of chronic Q fever with endocarditis requires a combination of doxycycline and quinolone antibiotics, and the course of therapy may take three to four years.
An effective vaccine against Q fever has been developed, and it is recommended for use by those with occupational risks for infection. The vaccine is not commercially available in the United States, but it can be obtained through government agencies such as the U.S. Army Medical Research Institute of Infectious Diseases. Pasteurization of milk usually kills the bacteria, but Coxiella can survive at 60° Fahrenheit (pasteurization temperature normally is set at 62.9° Fahrenheit, leaving a relatively small margin of error).
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