What is Q fever?
Q fever is a disease caused by the bacterium Coxiella burnetii. C. burnetii occurs worldwide and is generally spread to humans from a range of infected animals, such as goats, sheep, cows, cats, dogs, rodents, and some birds. Small ruminants, however, are the commonest source. It takes its name from the fact that its cause was, for a long time unknown and it became referred to as Query (Q) fever. It was first recognised in abattoir workers in Australia in 1935. In animals, Q fever tends to produce reproductive disorders such as abortion, in particular in goats. Q fever is a notifiable disease in Ireland.
How common is Q fever?
Q fever is found worldwide. Between 12 and 17 cases of Q fever are reported in Ireland each year. Most cases are sporadic; outbreaks do occur but are uncommon and tend to be seen in those who have not had the chance to develop immunity (i.e. city dwellers). Q fever tends to be more common during the lambing season, but it occurs year round. Since 2007, there has been an extensive outbreak in The Netherlands resulting in more than 3000 human cases diagnosed. Cases tend to live close to areas of intensive goat farming.
Who is at risk of developing Q fever?
The disease is commonly acquired through occupational exposure to infected sheep and other small ruminants, e.g. by farmers, veterinarians, and abattoir workers. Risk appears to be greatest at parturition or during abortions and during dry, windy weather conditions.
What are the symptoms of Q fever?
More than half of those who acquire Q fever, have no symptoms. Most symptomatic cases present acutely in one of three ways:
- Flu-like form: an illness resembles influenza with a fever, chills and headache and muscle aches. Onset tends to be quite sudden; this form is the commonest variety.
- Pneumonia: generally mild with cough being prominent.
- Hepatitis: this is generally mild and short lived.
Occasionally, a more chronic form may develop with endocaridits, prolonged refractory hepatitis and neurological complications (most commonly meningoencephalitis).
In most cases, the illness is of short duration, lasting less than two weeks, even without treatment, but in some cases fever can persist for as long as two months. The more chronic form of Q fever generally lasts at least six months. Recovery is almost always the rule for the acute form of the disease; fully recovery from the chronic form is more variable. So serious is it that endocardial involvement carries a fatality rate of as much as 50%.
How is Q fever spread to humans?
People become infected by inhaling contaminated dust, or from contact with urine, faeces, vaginal mucus or semen of infected animals. Contaminated bedding and litter can be infectious. There is no evidence that consumption of milk or milk products results in human disease, but care should be taken to consume only pasteurised milk. Direct contact with infected animals and contaminated materials, such as wool, straw, fertilizer, and laundry has been associated with spread of the disease. The incubation period - time from initial infection to the appearance of symptoms - is from 9 to 40 days (typically 14-20 days).
Who is most at risk from Q fever?
Q fever can cause problems in pregnancy. If a mother becomes infected during pregnancy, this can lead to premature birth, low birth weight, and spontaneous abortion. Immunosupressed patients such as those living with cancer and patients with heart disease and heart or vascular grafts are also at higher risk. Men are more commonly infected than women (this is probably related to the fact that men, on average, spending more time working on the land and with animals). People who own pets and who drink raw milk are also more likely to have been exposed to Q fever.
How is Q fever diagnosed and treated?
Q fever is diagnosed by a simple blood test to measure Q fever antibodies. Treatment is not generally necessary. If symptoms are severe or prolonged, a course of antibiotics may be necessary. The drugs of first choice are doxycycline or tetracycline for 7-14 days. The chronic form requires much longer term antibiotics and relapses are common.
What can be done to prevent Q fever?
It is important that pregnant women and immunosuppressed patients should avoid close contact with sheep and lambs during the lambing season. In addition, exposure to cattle, goats or cats, which are in the process of giving birth or in the post-partum period, should also be avoided. There is no vaccine available against Q fever.
Updated 2nd July 2010