Coxiella burnetii is a bacterium that infects the feces, urine, and milk of animals such as sheep, cattle, and goats. The amniotic fluid and placenta of pregnant animals contain high levels of the bacteria. Coxiella burnetii causes acute or chronic Q fever. The Q stands for "query" because, when researchers named the illness, the cause was unknown; they initially believed C. burnetii only infected animals. In 1940, experts identified the cause and effect relationship of the bacteria and subsequent fever.
Humans contract Coxiella burnetii primarily from breathing in dust contaminated with feces and urine of infected animals. Less common sources of infection are direct contact with animals and consuming unpasteurized milk or dairy products from infected livestock. C. burnetii can also transfer through blood transfusions and from mother to child during childbirth, but these routes are rare.
Veterinarians, people who work in meat processing or dairy industries, livestock farmers, and animal researchers are at increased risk of contracting C. burnetii, though it is more common in older people. Men have higher rates of infection because on average more men have jobs in high-risk fields than women. People with a history of heart valve defects and other heart conditions are more likely to develop chronic infections and complications. Those with weakened immune systems, and pregnant women, are also at higher risk of chronic infection.
Almost half of C. burnetii infections are asymptomatic. For the other percentage, symptoms of acute Q fever appear two or three weeks after exposure to the bacterium. Nausea, vomiting, stomach pain, and diarrhea are common. Other symptoms include high fever, fatigue, severe headache, lethargy, chills, chest or muscle pain, and a non-productive cough. Acute Q fever usually doesn't require treatment.
Approximately five percent of people infected with C. burnetii develop a chronic Q fever. Symptoms include fevers and chills, fatigue, shortness of breath, weight loss, and swelling in the arms or legs. Chronic Q fever can occur within weeks of exposure, or it can develop years later. Pregnant women may experience complications (discussed next) of chronic infection related to pregnancy without displaying any other symptoms.
Q fever, especially a chronic infection, can cause serious complications that may be fatal without hospitalization. Complications include infection of heart tissue, endocarditis, inflammation of the brain and nervous system or encephalitis, pneumonia, hepatitis, and an enlarged spleen. Pregnant women are at risk of miscarriage, stillbirth, premature delivery, and low infant birth weight.
Most C. burnetii infections in the U.S. occur in western and plains states, due to the prevalence there of livestock and ranching. Over a third of all U.S. infections are in California, Texas, Colorado, and Illinois; occasionally, people report infections after traveling outside the country. Worldwide, C. burnetii worldwide is common anywhere humans raise livestock; infection rates in developing nations can be higher, as well.
Spore-forming bacteria are almost always hard to treat and C. burnetii presents additional challenges. Routine administration of antibiotics in livestock is common in the U.S. and many other nations. Livestock infected with C. burnetii do not display symptoms and usually carry the bacteria throughout their lives. Unfortunately, these factors result in continuous exposure to multiple antibiotics, so C. burnetii is now resistant to several antibiotic classes.
Q fever shares so many initial symptoms with other common illnesses that medical history and circumstances are essential for a correct diagnosis. Contact with livestock or work in a high-risk profession should raise a doctor's suspicion of C. burnetii exposure. Medical professionals test patients' blood to look for antibodies. This sign is not detectable in the first seven to fifteen days of the illness, however, so doctors frequently start antibiotic therapy immediately instead of waiting for laboratory results to confirm the diagnosis.
The CDC recommends chronic Q fever be supervised by experienced physicians. People with this infection require months of antibiotic therapy. A normal course of treatment includes two or three types of antibiotic, due to the bacteria's multi-drug resistance. The dosage and type of antibiotic the doctor will prescribe vary with each case. The dosage necessary to cure the infection frequently reaches the point of toxicity, making it even more important medical professionals consistently monitor patients with blood draws and labwork.
C. burnetii can travel long distances by wind and survives for long periods in the environment. It is spore-forming bacteria and resistant to heat, dryness, and most common disinfectants. C. burnetti is also very contagious in specific circumstances. The infectious nature of the bacterium, its ability to survive adverse conditions, and the difficulty in treating chronic infections led to its development as a weapon of bioterrorism, the intentional use of an infectious agent to cause harm to humans, livestock, or crops. The CDC made C. burnetii a nationally notifiable disease in 1999 and tracks every reported case of Q fever in the United States.
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