Q Fever

How Q fever is spread from animals

Q fever is caused by bacteria known as coxiella burnetii (or c. burnetii). The bacteria are usually spread to animals by infected ticks. Samples of c. burnetii have been found in almost all types of animals, including reptiles and fish.

The most commonly affected animals, and those that pose the biggest risk to humans, are:

• sheep,
• cows,
• goats, and
• domesticated pets, such as dogs, cats and guinea pigs.

Most animals with Q fever do not experience any symptoms, so it can be difficult to tell if an animal is infected. However, the bacteria can cause an increase in miscarriages among an infected herd of cows or flock of sheep.

The bacteria can be released by an infected animal through its:

• urine,
• milk,
• faeces, and
• birth by-products, such as the placenta (the organ that connects a foetus to its mother’s womb), which is sometimes known as the afterbirth.

Birth by-products pose the greatest risk because they contain a high number of c. burnetii bacteria. For example, it is estimated that one gram of infected placenta contains enough bacteria to infect 100 million guinea pigs with Q fever.

How Q fever is spread to humans

Q fever can be spread to humans by both direct and indirect exposure to infected animals.

Direct exposure

The most common type of direct exposure occurs when a person breathes in small particles released by infected animals, particularly when animals are being slaughtered or giving birth.

Indirect exposure

The c. burnetii bacteria are tough and can survive in the outside environment for up to 10 months. Many cases of indirect exposure are caused when contaminated soil, dust, hay or other substances are spread by the wind over a wide area.

In 2003, there was a large outbreak of Q fever in an Italian prison. It is thought to have been caused by exposure to contaminated dust created by infected sheep that were grazing in a nearby field.

Drinking unpasteurised milk from an infected animal may also expose you to Q fever. Unpasteurised milk is milk that has not been treated with heat to kill off bacteria.

Human to human transmission

It is thought that you cannot catch Q fever by close bodily contact with an infected person or through an infected person coughing or sneezing.

Most experts believe that Q fever can only be transmitted from one human to another through:

• sexual intercourse, or
• by a pregnant woman passing on the infection to her unborn child.

Chronic Q fever

It is unclear why some people go on to develop the chronic form of Q fever. Most cases of chronic Q fever develop in people with a pre-existing health condition, which makes them more vulnerable to infections. These health conditions include:

• heart disease, particularly disease that affects the valves of the heart, such as stenosis (narrowing of the valve),
• kidney disease, and
• cancers that affect the blood, such as lymphoma and leukaemia.

Vulnerability to infection is higher in people with a weakened immune system, either due to a health condition, such as HIV or AIDS, or as a side effect of certain medical treatments, such as chemotherapy or long-term steroid use.