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Q fever
Overview
Q fever is a zoonotic disease caused by Coxiella burnetii, a species of bacteria that is distributed globally. Many cases of Q fever in humans are not obvious or diagnosed, so the disease is thought to be widely underreported. Cattle, sheep, and goats are the primary reservoirs of C. burnetii, but infection has been noted in a wide variety of other animals, including other species of livestock and in domesticated pets. Coxiella burnetii does not usually cause clinical disease in these animals, although abortion in goats and sheep has been linked to C. burnetii infection. Infection can be excreted in milk, urine, and feces of infected animals, and especially in amniotic fluids and the placenta during animal birthing. The bacteria are resistant to heat, drying, and many common disinfectants, enabling them to survive for long periods in the environment.
How is it spread to humans?
Infection of humans usually occurs by inhalation of barnyard dust that is contaminated by dried placental material, birth fluids, and excreta of infected herd animals. Humans are often very susceptible to the disease. Ingestion of contaminated milk, followed by regurgitation and inspiration of the contaminated food, are less common modes of transmission. Other modes of transmission to humans, including tick bites and human to human transmission, are rare.
Signs and Symptoms
Only about one-half of all people infected with C. burnetii show signs of illness. Most patients become ill within 2-3 weeks of exposure, and symptoms of acute exposure are sudden onset of one or more of the following:
- high fevers (up to 104-105° F)
- severe headache
- general malaise
- myalgia
confusion
- sore throat
- chills
- sweats
- non-productive cough
- nausea
- vomiting
- diarrhea
- abdominal pain
- chest pain.
Fever usually lasts for 1 to 2 weeks. Weight loss can occur and persist for some time. 30-50%percent of patients with a symptomatic infection will develop pneumonia. Additionally, a majority of patients have abnormal results on liver function tests and some will develop hepatitis. In general, most patients will recover to good health within several months without any treatment. Only 1%-2% of people with acute Q fever die of the disease.Chronic Q fever, characterized by infection that persists for more than 6 months is uncommon but is a much more serious disease. Patients who have had acute Q fever may develop the chronic form as soon as 1 year or as long as 20 years after initial infection.
A serious complication of chronic Q fever is damaged heart valves. Those with pre-existing valvular heart disease, history of vascular graft, transplant recipients, patients with cancer, and those with chronic kidney disease are at increased risk of developing chronic Q fever. As many as 65% of persons with chronic Q fever may die of the disease.
Diagnosis
Because the signs and symptoms of Q fever are not specific to this disease, it is difficult to make an accurate diagnosis without appropriate laboratory testing. A platelet count can help indicate Q fever, and either serologic testing (indirect immunofluorescence assay) or tissue examination (immunohistochemical staining, DNA detection) are required to make a definitive diagnosis.
Treatment
Doxycycline or Quinolone are the treatments of choice for acute Q fever. Antibiotic treatment is most effective when initiated within the first 3 days of illness. Therapy should be started again if the disease relapses.
Chronic Q fever endocarditis is much more difficult to treat effectively and often requires the use of multiple drugs.
Prevention
In the United States, Q fever outbreaks have resulted mainly from occupational exposure involving veterinarians, meat processing plant workers, sheep and dairy workers, livestock farmers, and researchers at facilities housing sheep. Prevention and control efforts should be directed primarily toward these groups and environments.The following measures should be used in the prevention and control of Q fever:
- Educate at-risk populations 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.
Significance for Bioterrorism
Coxiella burnetii is a highly infectious agent that is rather resistant to heat and drying. It can become airborne and inhaled by humans. A single C. burnetii organism may cause disease in a susceptible person. This agent could be developed for use in biological warfare and is considered a potential terrorist threat.
Source: CDC
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