What is Q Fever?

Q fever is a disease caused by the bacterium Coxiella burnetii which mainly afflicts sheep and cattle but can be transmitted to humans who come into contact with infected animals.
Symptoms resemble those of influenza and include fever,
headache and lung inflammation.

Statistics

Q fever is present throughout the United States, and is a notifiable disease in this country. Despite this, its precise incidence is unknown. Q fever exists worldwide. Studies of European countries have shown incidence of the disease of 5-30%, with lower figures seen in urban areas and higher figures in rural areas.
The mortality rate with acute infection is reportedly as high as 2.4% but generally is less than 1%. Males are affected more than females.

Risk Factors

Cattle, sheep, and goats are the primary reservoirs of C. burnetii. 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. The organisms are excreted in milk, urine, and faeces of infected animals.
Most importantly, during the birth process the organisms are shed in high numbers within the amniotic fluids and the placenta. The organisms are resistant to heat, drying, and many common disinfectants, and these features allow the bacteria to survive for long periods in the environment.
Infection of humans usually occurs by inhalation of these organisms from air that contains airborne barnyard dust contaminated by dried placental material, birth fluids, and excreta of infected herd animals. Humans are often very susceptible to the disease, and very few organisms may be required to cause infection.
Ingestion of contaminated milk, followed by regurgitation and inspiration of the contaminated food, is a less common mode of transmission. Other modes of transmission to humans, including tick bites and human to human transmission, are rare.1

Progression

The incubation period for Q fever varies depending on the number of organisms that initially infect the patient. Infection with greater numbers of organisms will result in shorter incubation periods. Most patients become ill within 2-3 weeks after exposure. Most patients with acute disease will recover without treatment, however few may develop chronic disease, which is usually fatal if untreated. Those who recover fully from infection may possess lifelong immunity against re-infection.

How is it Diagnosed

Tests that will aid the physician in making the diagnosis of Q fever include:

  • blood tests to ascertain levels of cells in the blood.
  • liver function tests to determine if the liver is inflamed.
  • a chest x-ray to detect pneumonia .

 

Prognosis

The prognosis with acute Q fever is excellent, with a low mortality rate (about 1%) in hospitalized patients. Children usually are more mildly affected than adults.

Treatment

Doxycycline is the treatment of choice for acute Q fever, and is most effective when initiated within the first 3 days of illness. A dose of 100 mg of doxycycline taken orally twice daily for 15-21 days is a commonly prescribed regime. Quinolone antibiotics may also be considered by the physician. 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. Two different treatment protocols have been evaluated:
1) doxycycline in combination with quinolones for at least 4 years and,
2) doxycycline in combination with hydroxychloroquine for 1.5 to 3 years.
The second therapy leads to fewer relapses, but requires routine eye exams to detect accumulation of chloroquine. Surgery to remove damaged valves may be required for some cases of endocarditis.

References

[1] Centres for Disease Control and Prevention. Q Fever [online]. 13 February 2003, Available from http://www.cdc.gov/ncidod/dvrd/qfever/
[2] Edlow, JA. Tick-borne diseases, Q Fever [online]. eMedicine Article, 25 April 2005, Available from http://www.emedicine.com/EMERG/topic589.htm
[3] Kumar, P & Clark, M. Clinical Medicine, Fourth Edition. WB Saunders, London, 1998.