Q fever is a disease of humans and some animals that is caused by a bacterium called Coxiella burnetii. The infection is a zoonosis—it is passed to humans by contact with infected animals that are not usually harmed by the organism. The animals typically affected are sheep, cattle, and goats. Q fever can occur and clear quickly (this type is called an acute infection), or can persist for a much longer time (this is called a chronic infection).
WORDS TO KNOW
ACUTE: An acute infection is one of rapid onset and of short duration, which either resolves or becomes chronic.
GRAM-NEGATIVE BACTERIA: All types of bacteria identified and classified as a group that does not retain crystal-violet dye during Gram's method of staining.
ZOONOSES: Zoonoses are diseases of microbiological origin that can be transmitted from animals to people. The causes of the diseases can be bacteria, viruses, parasites, and fungi.
Q fever was first described in Australia in 1935 by the physician Edward H. Derrick (1898–1976) in people working in an Australian slaughterhouse. At the time, the cause for the illnesses was unknown; hence the term Q, which was short for Query. In 1937, C. burnetii was isolated and identified. The following year, the same organism was isolated from ticks in Montana, leading researchers to suspect a tick-mediated animal-human connection. The U.S. researchers also showed that the microbe was a type of bacterium called a rickettsia. Rickettsia are important from the standpoint of infectious diseases. As an example, other rickettsia are responsible for the potentially serious diseases called Rocky Mountain spotted fever and trench fever.
C. burnetti is a gram-negative organism, meaning it has two membranes surrounding the inner contents of the cell. In addition, the bacterium requires a host cell in order to grow and divide. This is similar to viruses. However, unlike viruses, which are not considered to be alive, C. burnetii is living and can survive, but cannot grow and divide, when not in a host cell.
The bacteria can survive for a long time in the natural environment, as they are not easily killed by heat, dryness, and even chemical compounds that readily kill other bacteria. This makes it more likely that the bacteria will be spread to those who come into contact with them.
Q fever results from inhalation of the bacteria. Infections have been traced to the inhalation of bacteria dislodged into the air from dry hay or a dusty barnyard. Only a few living organisms need be inhaled to establish an infection. This route of infection is different from other rickettsial diseases, where the bacteria are transferred from animal to human by tick bites. People who are most a trisk of acquiring Q fever are those who are around animals like goats, sheep, and cattle, since these animals can naturally harbor the bacterium. The bacteria can be present in the milk, urine, amnioticfluid, and feces of the animals. Also, bacteria canbe present in amniotic fluid and the placenta, and so can be spread to people who help in the birth of animals. Veterinarians, processing plant workers, and livestock farmers are more susceptible to Q fever than the general population.
For reasons that are not clear, only about 50% of those people who inhale the bacteria display symptoms. The symptoms include a sudden and high fever, a flulike sickness, severe headache, nausea with vomiting, abdominal pain, and a general feeling of being unwell. People can lose weight during their illness, which can take some time to regain following their recovery. Only 1–2% of those with the milder form of Q fever die of the illness.
A serious lung infection (pneumonia) can develop in 30–50% of people with Q fever. Liver damage including hepatitis can also occur. These symptoms usually ease in several months. However, a more persistent form of Q fever can develop, resulting in debilitating damage to heart valves due to the longer-lasting infection that kills up to 60% of those who acquire the chronic infection.
There are two different forms of C. burnetii that differ in the types of molecules present on the outer surfaces of their cells. The two forms have been designated phase I and phase II. The phase I form is associated with the chronic form of Q fever.
The short-term form of Q fever does not always immediately lead to the longer form; indeed, the chronic form of Q fever can develop in the absence of the milder form of the disease. The time lag between the short-term and chronic forms of Q fever can be as long as several decades.
The bacterium responsible for Q fever occurs worldwide. Countries such as Australia and the United States with a heavier emphasis on livestock agriculture, or which have a greater prevalence of animals that naturally harbor the bacterium, have a higher occurrence of the disease.
Diagnosis of Q fever most typically involves the detection of antibodies to C. burnetii or genetic material from the bacterium. Growing the organism is difficult, so detection of the bacterium itself is not typically accomplished. Following diagnosis, treatment consists of antibiotic therapy. Typically, this is effective, although the therapy will be necessary for years when the infection is chronic. Heart valve damage can require replacement of the defective tissue.
A vaccine for Q fever exists. As of 2007, it is available in Australia and parts of Europe, but is not yet widely available in North America. Beginning in 2001, people at risk in Australia could be vaccinated. North Americans identified at higher risk of Q fever can also now be vaccinated. Similarly, a vaccine for animals exists, but is not yet in widespread use in North America.
Prevention of the transmission of the bacterium to humans involves wearing masks when around domestic livestock and the prompt disposal of the placenta and other tissues resulting from the birth process.
IN CONTEXT: SOCIAL AND PERSONAL RESPONSIBILITY
The Division of Viral and Rickettsial Diseases at the Centers for Disease Control and Prevention (CDC) states that the following measures should be used in the prevention and control of Q fever:
- Educate the public on sources of infection.
- Appropriately dispose of placenta, birth products, fetal membranes, and aborted fetuses at facilities housing sheep and goats.
- Restrict access to barns and laboratories used in housing potentially infected animals.
- Use only pasteurized milk and milk products.
- Use appropriate procedures for bagging, autoclaving, and washing of laboratory clothing.
- Vaccinate (where possible) individuals engaged in research with pregnant sheep or live C. burnetii.
- Quarantine imported animals.
- Ensure that holding facilities for sheep should be located away from populated areas. Animals should be routinely tested for antibodies to C. burnetii, and measures should be implemented to prevent airflow to other occupied areas.
- Counsel persons at highest risk for developing chronic Q fever, especially persons with pre-existing cardiac valvular disease or individuals with vascular grafts.
Q fever can be a potentially serious disease because it can be spread from animals to people. In the United States, cases of the illness have been required to be reported to the Centers for Disease Control and Prevention since 1999. Imported livestock are also monitored for the presence of the bacterium, since transfer to other domestic animals could occur unknowingly in the absence of development of any symptoms in these hosts.
Why only about 50% of infected people display symptoms of infection is still unclear, but is important to learn if vaccines are to be fully protective. Research is underway to try and distinguish factors associated with people, the bacterium, or both that help some people ward off the consequences of infection. Additionally, it is not clear why Q fever does not persist for a long time in some people, but becomes a chronic, destructive, and potentially life-threatening condition in others.
Tierno, Philip M. The Secret Life of Germs: What They Are, Why We Need Them, and How We Can Protect Ourselves Against Them. New York: Atria, 2004.
Anderson, Alicia D. “Q Fever and the U.S. Military.” Emerging Infectious Diseases. 11:1320–1323 (2005).
Centers for Disease Control and Prevention. “Q Fever.” <http://www.cdc.gov/ncidod/dvrd/qfever/index.htm> (accessed May 1, 2007).
Q fever is an illness caused by a type of bacteria, Coxiella burnetii, resulting in a fever and rash.
C. burnetii lives in many different kinds of animals, including cattle, sheep, goats, ticks, cats, rabbits, birds, and dogs. In sheep and cattle, for example, the bacteria tends to accumulate in large numbers in the female's uterus (the organ where lambs and calves develop) and udder. Other animals have similar patterns of bacterial accumulation within the females. As a result, C. burnetii can cause infection through contaminated milk, or when humans come into contact with the fluids or tissues produced when a cow or sheep gives birth. Also, the bacteria can survive in dry dust for months; therefore, if the female's fluids contaminate the ground, humans may become infected when they come in contact with the contaminated dust.
Persons most at risk for Q fever include anybody who works with cattle or sheep, or products produced from them. These include farm workers, slaughterhouse workers, workers in meat-packing plants, veterinarians, and wool workers. Since September 2001, however, Q fever has become an additional concern because of its potential as an agent of bioterrorism.
Causes and symptoms
C. burnetii causes infection when a human breathes in tiny droplets, or drinks milk, containing the bacteria. After three to 30 days, symptoms of the illness appear.
The usual symptoms of Q fever include fever, chills, heavy sweating, headache, nausea and vomiting, diarrhea, fatigue, and cough. Also, a number of other problems may present themselves, including inflammation of the liver (hepatitis); inflammation of the sac containing the heart (pericarditis ); inflammation of the heart muscle itself (myocarditis ); inflammation of the coverings of the brain and spinal cord, or of the brain itself (meningoencephalitis); and pneumonia.
Chronic Q fever occurs most frequently in patients with other medical problems, including diseased heart valves, weakened immune systems, or kidney disease. Such patients usually have about a year's worth of vague symptoms, including a low fever, enlargement of the spleen and/or liver, and fatigue. Testing almost always reveals that these patients have inflammation of the lining of the heart (endocarditis ).
Q fever is diagnosed by demonstrating that the patient's immune system is making increasing numbers of antibodies (special immune cells) against markers (antigens) that are found on C. burnetii.
Doxycycline and quinolone antibiotics are effective for treatment of Q fever. Treatment usually lasts for two weeks. Rifampin and doxycycline together are given for chronic Q fever. Chronic Q fever requires treatment for at least three years.
Minocycline has been found to be useful in treating post-Q fever fatigue. The dosage is 100 mg per day for three months.
Death is rare from Q fever. Most people recover completely, although some patients with endocarditis will require surgery to replace their damaged heart valves.
Q fever can be prevented by the appropriate handling of potentially infective substances. For example, milk should always be pasteurized, and people who work with animals giving birth should carefully dispose of the tissues and fluids associated with birth. Industries which process animal materials (meat, wool) should take care to prevent the contamination of dust within the plant.
Vaccines are available for workers at risk for Q fever.
Beers, Mark H., MD, and Robert Berkow, MD, editors. "Biological Warfare and Terrorism." In The Merck Manual of Diagnosis and Therapy. Whitehouse Station, NJ: Merck Research Laboratories, 2004.
Beers, Mark H., MD, and Robert Berkow, MD, editors. "Q Fever." In The Merck Manual of Diagnosis and Therapy. Whitehouse Station, NJ: Merck Research Laboratories, 2004.
Arashima, Y., K. Kato, T. Komiya, et al. "Improvement of Chronic Nonspecific Symptoms by Long-Term Minocycline Treatment in Japanese Patients with Coxiella burnetii Infection Considered to Have Post-Q Fever Fatigue Syndrome." Internal Medicine 43 (January 2004): 1-2.
Gami, A. S., V. S. Antonios, R. L. Thompson, et al. "Q Fever Endocarditis in the United States." Mayo Clinic Proceedings 79 (February 2004): 253-257.
Madariaga, M. G., J. Pulvirenti, M. Sekosan, et al. "Q Fever Endocarditis in HIV-Infected Patient." Emerging Infectious Diseases 10 (March 2004): 501-504.
Wortmann, G. "Pulmonary Manifestations of Other Agents: Brucella, Q Fever, Tularemia and Smallpox." Respiratory Care Clinics of North America 10 (March 2004): 99-109.
Antibodies— Specialized cells of the immune system that can recognize organisms that invade the body (such as bacteria, viruses, and fungi). The antibodies are then able to set off a complex chain of events designed to kill these foreign invaders.
Antigens— Markers on the outside of bacteria or viruses which can be recognized by antibodies.
Bioterrorism— The use of disease microorganisms to intimidate or terrorize a civilian population.
Immune system— The system of specialized organs, lymph nodes, and blood cells throughout the body which work together to prevent foreign invaders (bacteria, viruses, fungi, etc.) from taking hold and growing.
Inflammation— The body's response to tissue damage. Includes increased heat, swelling, redness, and pain in the affected part.
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.
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.
See also Bacteria and bacterial diseases; Zoonoses
Q fever is an infectious disease caused by the bacterium Coxiella burnetii. The "Q" derives from "query" fever, its name before the true cause of the disease was discovered in 1937. Worldwide in occurrence, the etiologic agent is prevalent in sheep, cattle, and goats, and it is also found in ticks, rodents, birds, dogs, and rabbits. Infections in animals are usually inapparent, but the disease can cause spontaneous abortions in animals. Humans can be very susceptible and can contract the disease through inhalation of contaminated dust or particles from animal hides, excreta, and birthing materials.
Because C. burnetii proliferates within human white blood cells called monocytes, it is protected from part of the human immune system. A complex molecule called a lipopolysaccharide, found on the surface of the organism, further protects it from host serum defense factors. Human disease will usually present with sudden onset of headache, fever, chills, muscle soreness, and (sometimes) pneumonia. Hepatitis or endocarditis are rarer complications. Without modern detection methods, the disease is difficult to diagnose, and many human infections are probably unrecognized. It is suspected that host and microbial factors combine to determine the severity of human disease.
The antibiotic tetracycline is usually very effective in treating acute Q fever. Chronic inflammatory forms of the disease, such as Q fever endocarditis or hepatitis, require more than one year of antibiotic treatment.
Outbreaks of human Q fever are commonly reported in Asia, Australia, and parts of Europe. The disease was made reportable in the United States in 1999. Transmission from human to human is uncommon. Control of Q fever depends upon its recognition in animal populations and the culling of infected animals to prevent subsequent human exposure. A commercial vaccine, Qvax, is available in Australia.
Herb A. Thompson
(see also: Communicable Disease Control )
Maurin, M., and Raoult, D. (1999). "Q Fever." Clinical Microbiology Reviews 12(4):518–553.