Q fever is related to rickettsial diseases and is caused by Coxiella burnetii, which live mainly in sheep, cattle, and goats.
- Some people have mild symptoms, but most 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, a severe disease that can affect the heart.
- If people may have been exposed to sheep, cattle, or goats and doctors suspect Q fever, they may do blood tests and examine a sample of infected tissue to confirm the infection.
- People with Q fever are treated with an antibiotic, usually for a few weeks, but if chronic Q fever develops, treatment is needed for months or years.
The bacteria that cause Q fever, like rickettsiae, can live only inside the cells of other organisms.
Q fever occurs worldwide. The bacteria that cause Q fever live
mainly in sheep, cattle, and goats.
Infected animals shed the bacteria in their milk, urine, and stool (feces). People are infected when they inhale airborne droplets containing the bacteria or consume contaminated raw (unpasteurized) milk. Very rarely, the disease is transmitted from person to person.
Infected animals shed the bacteria in their milk, urine, and stool (feces). People are infected when they inhale airborne droplets containing the bacteria or consume contaminated raw (unpasteurized) milk. Very rarely, the disease is transmitted from person to person.
People at risk of developing Q fever include the following:
- Veterinarians
- Meat processing plant workers
- Slaughterhouse and dairy workers
- Livestock farmers
- Researchers at laboratories where sheep are kept
- People who live within several miles downwind from a farm with infected animals
The bacteria that cause Q fever survives in dust and stool for months. Even a single bacterium can cause infection. Because of these characteristics, these bacteria are considered a potential biological warfare agent.
Symptoms
About 9 to 28 days after bacteria enter the body, symptoms begin
suddenly. Some people have mild or no symptoms. Other people have
flu-like symptoms.
Symptoms of Q fever include fever, a severe headache, chills,
extreme weakness, muscle aches, loss of appetite, and sweating, but no
rash. The lungs are often affected, causing a dry (unproductive) cough,
chest pain, and shortness of breath (caused by pneumonia). Symptoms may be severe in older people and in people who have been weakened (debilitated) by a disorder.
Occasionally, the liver is involved. People then have pain in the upper right part of the abdomen and sometimes jaundice.
Women who are infected during pregnancy have an increased risk of a miscarriage or delivery before the baby is due.
Chronic Q fever is a severe disease that occurs in fewer than 5% of infected people. The risk is greatest for the following:
- Pregnant women
- People whose immune system has been weakened by a disorder or drugs
- People who have a heart valve disorder
Chronic Q fever often involves the lining of the heart and heart valves (called Q fever endocarditis). It sometimes involves the bones, artificial (prosthetic) joints, and the liver.
Without treatment, only 1% of people with Q fever die, but death is more likely if the heart is affected.
Diagnosis
- Biopsy and testing of infected tissue
- Blood tests
- Sometimes a chest x-ray
Symptoms of Q fever resemble those of other disorders and thus do not help doctors with the diagnosis. If doctors suspect Q fever, they ask whether people were at or near a farm because the bacteria that cause Q fever live mainly in cattle, sheep, and goats.
To confirm the diagnosis, doctors may do an immunofluorescence assay
to check for antibodies in blood samples. However, doing the test once
is not enough. The test must be repeated 3 to 6 weeks later to check for
an increase in the antibody level. In addition, doctors use the polymerase chain reaction (PCR) technique
to enable them to detect the bacteria more rapidly. Thus, the antibody
tests do not usually help diagnose the infection immediately after
someone becomes ill but can help confirm the diagnosis later.
Doctors may do biopsies of infected tissue if there is an obvious site of infection.
If people have a cough or other respiratory symptoms, doctors take a chest x-ray.
Prevention
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 likely to be exposed (such as slaughterhouse
and dairy workers, livestock farmers, and laboratory workers). This
vaccine is not available in the United States.
Before giving people the vaccine, doctors do blood and skin tests
to determine whether people already have immunity to Q fever. If people
already have immunity, vaccinating them can cause severe reactions near
the injection site.
Treatment
-
Antibiotics
The initial infection is treated with the antibiotic doxycycline,
taken by mouth. People take the antibiotic until they improve and have
had no fever for about 5 days, but they must take it for at least 7
days. Typically, 2 to 3 weeks of treatment is required.
Q fever endocarditis
If the heart is affected, treatment is given for months to years.
Typically, treatment is given for at least 18 months, but some people
need to be treated their entire life. People are usually given doxycycline plus hydroxychloroquine.
Both are taken by mouth. To determine when treatment can be stopped,
doctors periodically examine the person and do blood tests.
However antibiotic treatment is often only partially effective,
and surgery is often needed to replace the damaged heart valves (see
figure Replacing a Heart Valve).
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