Q fever

What is Q fever?

Q fever is a widespread disease caused by the bacteria Coxiella burnetii, which is able to infect mammals, birds, reptiles and arthropods. It causes a mild disease in ruminants, but can cause abortions and still births in cattle, sheep and goats.

It is also a zoonosis, a disease of animals that can infect humans.

Q fever is listed in the WOAH Terrestrial Animal Health Code and Member Countries and Territories are obligated to report occurrences of the disease to the WOAH according to the WOAH Terrestrial Animal Health Code.

Transmission and spread

C. burnetii is shed in milk, urine and feces. But most importantly, during parturition, huge concentrations of bacteria, up to a billion per cubic centimetre, are found in the amniotic fluids and the placenta.

Outside the animal the bacteria becomes a small, dense, long lasting spore-like form which is able to resist heat and drying. It can then contaminate dust and be spread by wind for long distances. It so highly infectious that a single inhaled organism can cause clinical illness in an animal or person.

Outbreaks typically occur following a birth or abortion where the environment becomes contaminated with birthing fluids.

Q fever can also be spread by ticks which pass the bacteria from an infected to a susceptible animal, and whose faeces contain the bacteria thus also contaminating the environment. Since it is also shed in the milk of an infected animal, it can be contracted by drinking non pasteurised infected milk.

Public health risk

Because it is highly infectious for humans, Q fever is an important zoonosis, with veterinarians, laboratory workers, farmers and abattoir workers at risk. Surveys have shown that significant numbers of livestock handlers have antibodies indicating exposure to the organism.

Less than half of people infected become ill, and most infections are mild. But affected persons can develop a high fever with headache, muscle pains, sore throat nausea and vomiting, chest and stomach pains. The fever can last for one or two weeks, and lead to pneumonia or affect the liver. Treatment involves long term antibiotic therapy.

In a small percentage of cases, a chronic severe debilitating disease occurs. People with suppressed immune systems and those with pre-existing heart valve problems are at risk of this complication, which is often fatal. There is also a post Q  fever syndrome of chronic fatigue.

Q fever is the second most commonly reported laboratory infection with several recorded outbreaks involving 15 or more persons.

Clinical signs

Typically a mild disease of animals, mostly affecting cattle, sheep and goats, the most serious consequence is that it causes abortions late in the pregnancy.

Diagnostic

In samples from aborted or affected animals the diagnosis is confirmed by identifying the bacteria or more commonly using serological test to identify antibodies according to the standards found in the WOAH .

Prevention and control

Animal vaccination has been used in areas where the infections are common. More generally, sanitary measures to remove afterbirth and birth fluids, and to clean and disinfect areas where animals have given birth can prevent the disease from spreading. In the laboratory, strict controls are needed and C.  burnetii is to be handled under biosafety level 3  standards, as outlined in the WOAH Manual of Diagnostic Tests and Vaccines for Terrestrial Animals.

Geographical distribution

First identified in Australia in 1935, Q fever has since been found throughout the world with the exception of New Zealand.

Cattle, sheep, and goats are the primary reservoirs of C. burnetii. Infection has been noted in a wide variety of other domestic animals including dogs, cats, rabbits, horses, pigs, camels, buffalo, rodents, and some birds, that can transmit the infection to humans without showing signs of illness.

References

The Center for Food Security and Public Health, Iowa State University

Merck Veterinary Manual