Q fever is a rickettsia-like bacterial infection caused by Coxiella burnetii bacteria, which live mainly in sheep, cattle, and goats.
People are infected when they inhale airborne droplets containing the bacteria or consume contaminated raw (unpasteurized) milk.
Some people have mild symptoms, but some have flu-like symptoms, such as a fever, a severe headache, chills, a dry cough, extreme weakness, and muscle aches.
A few people develop chronic Q fever, which is a severe form of the infection that can affect the heart.
To diagnose the infection, doctors do blood tests.
People are given the antibiotic doxycycline and sometimes another medication to treat the infection.
Coxiella burnetii bacteria can be passed between people and animals and cause infections. Infections that can be passed between people and animals are called zoonotic diseases, or zoonoses (see Introduction to Diseases Spread Between Animals and People (Zoonoses)). See also Q Fever in Cats.
The bacteria that cause Q fever, like rickettsiae, can live and multiply only inside the cells of a host organism, such as an animal or a person, and cannot survive on their own in the environment.
Q fever occurs worldwide.
The bacteria that cause Q fever live mainly in sheep, cattle, and goats and occasionally in pets (the hosts). These bacteria are found in the milk, urine, feces, and tissues (such as the placenta) of infected animals (which often do not show symptoms). People are infected when they inhale contaminated airborne droplets or dust containing the bacteria or consume contaminated raw (unpasteurized) milk. Airborne droplets containing the bacteria can travel long distances through the wind. Very rarely, the disease is transmitted from person to person.
The bacteria that cause Q fever survives in dust and feces for months. Even a single bacterium can cause infection. Because of these characteristics, Coxiella burnetii bacteria are considered a potential biological warfare agent.
People at risk of developing Q fever include the following:
Veterinarians
Meat processing plant workers
Slaughterhouse and dairy workers
Livestock farmers
Ranchers
Researchers at laboratories where animals are kept
People who live within several miles downwind from a farm with infected animals
Q fever can be acute or chronic.
Chronic Q fever is a severe form of the infection. It occurs in fewer than 5% of infected people. It may develop from a few weeks to many years after the initial infection. People who are at high risk of developing chronic Q fever include the following:
Pregnant people
People whose immune system has been weakened by a disorder or medications
People who have a heart valve defect, a vascular graft (surgery to treat blood vessels that are narrowed or blocked), or an arterial aneurysm (a bulge in the wall of an artery)
People who are male and over 60 years of age
Symptoms of Q Fever
Within 2 to 3 weeks after people are exposed to the bacteria, they may develop symptoms.
Acute Q fever
Some people with acute Q fever do not have any symptoms.
In other people, symptoms of acute Q fever begin suddenly and include fever, a severe headache, chills, extreme fatigue, muscle aches, loss of appetite, and sweating. The lungs are often affected, causing a dry (unproductive) cough, chest pain, and shortness of breath (caused by pneumonia). An inflammation of the lungs may also occur (pneumonitis).
Sometimes, the liver is affected. People then have pain in the upper right part of the abdomen and sometimes yellowing of the skin and whites of the eyes (jaundice).
Acute Q fever does not cause a rash, but it may cause an infection in the brain such as meningitis and/or encephalitis. These brain infections cause high fevers, neck pain or stiffness, headaches, and confusion.
Pregnant people have an increased risk of a miscarriage or delivery before the baby is due.
Up to 20% of people with Q fever have severe fatigue (exhaustion), muscle pains, headache, eye sensitivity to light, changes in mood, and difficulty sleeping long after the acute Q fever infection has gone away. These lingering symptoms are called post-Q fever fatigue syndrome.
Chronic Q fever
Chronic Q fever is a severe form of the infection. It may develop from a few weeks to many years after the initial infection.
Chronic Q fever usually affects the lining of the heart and heart valves (called Q fever endocarditis) and the liver. It sometimes causes infection in the bones and in artificial (prosthetic) joints. In some people with Q fever endocarditis, a scattered, purple rash can occur.
Diagnosis of Q Fever
Blood tests
Biopsy and testing of infected tissue
Sometimes a chest x-ray
Symptoms of Q fever resemble those of other illnesses, such as the flu, and often do not help doctors with the diagnosis. If doctors suspect Q fever, they ask people whether they work with animals or have been around animals or animal products because Coxiella burnetii bacteria live mainly in cattle, sheep, and goats.
To confirm the diagnosis, doctors may take a blood sample and do an immunofluorescence assay to detect antibodies to the bacteria. This test may need to be repeated a few weeks later to detect a rise in antibodies. In addition, doctors use a blood sample or do a biopsy to remove a sample of infected tissue to do the polymerase chain reaction (PCR) technique. With the PCR technique, copies of the bacteria's DNA are made so that the bacteria can be detected more rapidly. See also Tests That Detect Antibodies to or Antigens of Microorganisms.
If people have a cough or other respiratory symptoms, doctors take a chest x-ray.
When doctors suspect a person has Q fever endocarditis, they may do an echocardiogram and blood cultures. An echocardiogram uses high-frequency (ultrasound) waves to produce a moving image of the heart, which allows doctors to examine the heart valves for disorders.
Treatment of Q Fever
An antibiotic and sometimes another medication
People who have acute or chronic Q fever are treated with medications.
Acute Q fever is fatal in very few people, even without treatment. Chronic Q fever endocarditis is always fatal without treatment, but with treatment, the risk of death is significantly lower.
Acute Q fever
For acute Q fever, people are treated with the antibiotic doxycycline taken by mouth (orally). People take the antibiotic until they improve, have not had a fever for about 5 days, and have been taking the antibiotic for about 2 weeks. People who have a severe infection may need to take the antibiotic longer.
Although doxycycline can cause tooth staining in children younger than 8 years old, a short, 5- to 10-day course of doxycycline in children of all ages is recommended by the American Academy of Pediatrics and can be used without causing tooth staining or weakening of tooth enamel.
Chronic Q fever and Q fever endocarditis
For chronic Q fever and Q fever endocarditis, treatment is given for at least 18 months, but some people need to be treated for months to years. People are given doxycycline and the antimalarial medication hydroxychloroquine. Both are taken by mouth. To determine when treatment can be stopped, doctors do periodic examinations and blood tests.
Medications are often only partially effective, and surgery is needed to replace the damaged heart valves (see figure ).
Prevention of Q Fever
Measures to prevent Q fever involve mainly using appropriate sanitation and testing (for the bacteria) in facilities where sheep, cattle, and goats are kept. Consuming only pasteurized milk and milk products can also help.
In Australia, a vaccine is available and has been used to prevent the infection in people who are likely to be exposed to Coxiella burnetii bacteria (such as slaughterhouse and dairy workers, veterinarians, livestock farmers, and laboratory workers). This vaccine is available only in Australia.
Before giving people the vaccine, doctors do blood and skin tests to determine whether people may already have had Q fever and developed immunity (antibodies) to the disease after their recovery. If people already have such immunity, vaccinating them can cause severe allergic reactions near the injection site.
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