Q fever: Description
Q fever belongs to the so-called zoonoses. These are diseases that can be transmitted from animals to humans. The causative agent of Q fever is a bacterium that likes to reside in dust or hay.
Because Q fever was first diagnosed in 1937 in the Australian state of Queensland among workers in slaughterhouses, the disease was initially called Queensland fever. However, Q fever has spread throughout the world. Epidemics with several hundred cases occur mainly in rural areas or on the outskirts of cities, because animals and humans live closer together here.
Q fever: symptoms
About half of all infected people show no symptoms (asymptomatic infection). In the other cases, mild flu-like symptoms develop, usually one to three weeks after infection (incubation period).
The acute infection
The disease lasts about two weeks and heals on its own. Pregnant women are at risk of miscarriage, especially if they contract the disease in the first trimester of pregnancy. In addition, the pathogen can be transmitted to the child.
The chronic infection
Very rarely, Q fever does not heal on its own, but becomes chronic: the scavenger cells of the immune system take up the pathogen, but cannot kill it. It then often remains inactive in the scavenger cells for a long time, waiting for a favorable opportunity to reactivate. This opportunity presents itself to it when the immune system is weakened by pregnancy or for other reasons. Then the Q fever pathogen can spread again in the body.
In particular, infection with Q fever during pregnancy is often chronic.
Q fever: causes and risk factors
Q fever is caused by the pathogen Coxiella burnetii. The bacterium primarily affects cloven-hoofed animals (cattle, sheep, goats). However, other animals such as cats, dogs, rabbits, deer, and birds can also act as its host. Even in various arthropods, mites, lice, flies and ticks, the Q fever pathogen has been found.
The bacteria are highly resistant to chemical and physical influences. They can therefore survive in dust, hay and other dry materials for up to two years.
How do humans become infected?
Birth products and contaminated newborns are also highly infectious. In addition, people can become infected with Q fever through the processing of meat and other animal products. Indirect transmission is possible via contaminated clothing. The route of infection via food from infected animals (raw milk, raw cheese) plays only a minor role.
It is also possible that the Q fever pathogen is transmitted directly from person to person (e.g., through contact with infected women in childbirth or via blood transfusions). However, this rarely happens. Infected pregnant women can, however, transmit the pathogen to the unborn child (the bacterium can multiply in the placenta).
Infected ticks are important vectors of Q fever between domestic and wild animals. In contrast, they play only a minor role as a source of infection for humans.
Risk groups
Q fever: examinations and diagnosis
Since the symptoms of Q fever can resemble many other diseases, the diagnosis is not easy to make. Important information is provided to the physician by the medical history (anamnesis), which he or she obtains in a conversation with the patient. Possible questions the doctor may ask include:
- Do you have a fever? If so, how long has it been present? What is the temperature?
- Do you have headaches or muscle aches?
- Do you keep pets or have a job involving animals or animal products?
Blood tests can confirm suspected Q fever. For this purpose, antibodies against the Q fever pathogen Coxiella burnetii are searched for in the patient’s blood sample. Based on the type of antibodies over time, one can also conclude on the course of the disease (acute or chronic).
Q fever: Treatment
Acute Q fever is usually treated with the antibiotic doxycycline. It usually must be taken for two to three weeks. During treatment, the liver values in the blood are monitored.
In certain cases, the attending physician prescribes other antibiotics or other medications in addition or as an alternative, as well as a longer duration of therapy – for example, in the case of chronic infection. There are also special considerations for pregnant women: Instead of doxycycline, they should take the better-tolerated antibiotic trimethoprim daily until the end of pregnancy. After birth, women should be examined for chronic Q fever infection.
However, antibiotic therapy is often only partially effective, and the heart valves damaged by inflammation must be replaced by prostheses in an operation.
Q fever: course of the disease and prognosis
Most Q fever infections heal on their own after one to two weeks. Sometimes, however, those affected continue to suffer from general fatigue for weeks (chronic fatigue syndrome). In very rare cases, the immune system is unable to fight the pathogen completely, so that the infection becomes chronic.
Q fever: prevention
The risk of contracting Q fever is increased in people who work with sheep, cattle, goats, or animal products such as meat, milk, or wool. Several measures have been shown to reduce the risk of infection. These include wearing and regularly decontaminating protective clothing, for example in dairy and meat processing, slaughtering and veterinary activities.
Pasteurizing potentially contaminated foods (such as milk) can also prevent infection with Q fever. Any pathogens in meat can also be killed by heating.
When a pregnant woman delivers with Q fever, the assisting personnel must follow strict hygiene measures.
