What is Q fever?

Definition

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.

Causes

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.

Risk Factors

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.

Symptoms

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.

Screening and Diagnosis

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.

Treatment and Therapy

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.

Prevention and Outcomes

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).

Bibliography

Lacasse, Alexandre, et al. “Q Fever.” eMedicine. Available at http://emedicine.medscape.com/article/ 227156-overview.

Madigan, Michael T., and John M. Martinko. Brock Biology of Microorganisms. 12th ed. Upper Saddle River, N.J.: Pearson/Prentice Hall, 2010.

Marrie, T. J., and D. Raoult. “ Coxiella burnetii (Q Fever).” In Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases, edited by Gerald L. Mandell, John F. Bennett, and Raphael Dolin. 7th ed. New York: Churchill Livingstone/Elsevier, 2010.

Parker, N. R., J. H. Barralet, and A. M. Bell. “Q Fever.” The Lancet 367 (February 25, 2006): 679-688.

Shakespeare, Martin. Zoonoses. 2d ed. London: Pharmaceutical Press, 2009.

Willey, Joanne M., Linda M. Sherwood, and Christopher J. Woolverton. Prescott, Harley, and Klein’s Microbiology. 7th ed. New York: McGraw-Hill, 2008.