Q fever
Q fever, also known as Coxiella burnetii fever, is an uncommon illness characterized by fever and pneumonia-like symptoms, primarily affecting individuals who work closely with infected farm animals. The disease is caused by the bacterium Coxiella burnetii, which is transmitted to humans mainly through inhalation of contaminated dust from animal waste or consumption of unpasteurized milk. Those at higher risk include workers in slaughterhouses, veterinarians, and individuals exposed to livestock, particularly cattle, sheep, and goats. Symptoms of acute Q fever can include severe headaches, high fever, chills, and respiratory issues, while chronic Q fever may lead to more severe complications like endocarditis. Diagnosis typically requires laboratory tests to detect antibodies against the bacterium. Treatment usually involves antibiotics like doxycycline, with chronic cases potentially requiring extended therapy. Vaccination is recommended for those at occupational risk, although it is not widely available in the United States. Preventative measures, such as pasteurizing milk, are also critical in reducing the risk of infection.
Q fever
- ANATOMY OR SYSTEM AFFECTED: All
- ALSO KNOWN AS: Coxiella burnetii fever, Q fever pneumonia, query fever
Definition
Q fever is an uncommon febrile, pneumonia-like illness most often contracted by people whose occupations involve 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.” However, the Q probably also refers to Queensland, the Australian province where 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 are at 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, people with cancer, and people with chronic kidney disease are at an increased risk of developing the more serious chronic form of the disease. Living near livestock or dairy farms, consuming unpasteurized dairy products, traveling to places where Q fever is known to exist, having a compromised immune system, and being pregnant are additional risk factors for Q fever.
Symptoms
The sudden onset of severe headache, high fever, chills, sweats, confusion, nausea, muscle pain, or general malaise most often characterizes the acute form of the illness. Other symptoms of the acute form of Q fever include respiratory issues, gastrointestinal upset, neurological symptoms, and skin rash. 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. Symptoms of the chronic form of Q fever include fatigue, weight loss, night sweats, shortness of breath, and swollen extremities. 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. It is also important to note that many individuals with Q fever will be asymptomatic.
Screening and Diagnosis
Diagnosing infection with C. burnetii requires an immunological or serological laboratory test to measure host antibodies to the pathogen. The indirect immunofluorescence assay (IFA) is widely used and most dependable. Still, immunohistochemical staining of infected tissue and deoxyribonucleic acid (DNA) isolation and identification by the polymerase chain reaction (PCR) are also utilized.
Treatment and Therapy
The preferred treatment is to start the patient on an immediate antibiotic regimen of doxycycline. It is typically prescribed as 100 milligrams, twice daily, for two to three weeks. Hydroxychloroquine has also proven useful. Treatment of chronic Q fever with endocarditis requires a combination of doxycycline and hydroxychloroquine antibiotics, and the course of therapy may take three to four years or longer.
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 can be obtained through government agencies such as the US Army Medical Research Institute of Infectious Diseases or requested from the Centers for Disease Control by a healthcare provider. Pasteurization of milk usually kills the bacteria, but Coxiella can survive at 60° Fahrenheit (pasteurization temperature is typically set at 62.9° Fahrenheit, leaving a relatively small margin of error).
Bibliography
"About Q Fever." CDC, 15 May 2024, www.cdc.gov/q-fever/about/index.html. Accessed 28 Sept. 2024.
Clark, Nicholas J., and Ricardo J. Soares Magalhães. "Airborne Geographical Dispersal of Q Fever from Livestock Holdings to Human Communities: A Systematic Review and Critical Appraisal of Evidence." BMC Infectious Diseases, vol. 18, no. 218, 2018, doi.org/10.1186/s12879-018-3135-4.
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)." 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, vol. 367, 25 Feb. 2006, pp. 679-688.
Patil, Sachin. "Q Fever - StatPearls." NCBI, 18 Nov. 2022, www.ncbi.nlm.nih.gov/books/NBK556095. Accessed 28 Sept. 2024.
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.