Babesiosis (tick fever)

The disease babesiosis is caused by a single-celled organism that is spread through a tick bite. The Babesia uses both the tick and the host to reproduce. It is not only transmitted to animals, but humans can also become infected. When an infected tick bites its host, the protozoan enters the body. It causes the red blood cells to be broken down and it mainly occurs in people who no longer have a spleen. It can lead to serious complaints.


This disease is an infection caused by the single-celled organism (protozoan) Babesia. This is transmitted to the host by a tick. In most cases this is an animal, but it can also be transmitted to humans. This disease is also called tick fever or piroplasmosis. It is quite rare for a human to be infected. In the past, this condition was limited to the southern warm countries within Europe. Nowadays, a species of tick that spreads this disease is also present in the Netherlands.

The complaints

After a bite from the infected tick, the incubation period will usually be between one week and three weeks. It will take six weeks at most. The complaints manifest themselves in fever, headache and muscle pain. Because the red blood cells are broken down, anemia can develop. In people who have had their spleens removed, the infection can lead to serious illness and even death. The complaints in these people are usually high fever, anemia, jaundice, dark urine and kidney failure.


Since 2004 it has also occurred in the Netherlands. It was first observed in dogs. It can also occur in cattle, deer, sheep and mice. Symptoms of the disease seen in these dogs were: shortness of breath, fever, red urine and sudden death. An animal can become infected through a tick bite if the tick has previously engorged itself with blood from an infected animal. It takes one to two days for the Babesia to become contagious. It is therefore important to remove a tick on both humans and animals as quickly as possible. Use preventive pesticides against ticks for animals. The protozoan Babesia occurs worldwide and is related to the malaria parasite. That is why complaints also resemble malaria. The disease can also be transmitted through a blood transfusion. People who have had their spleen removed are more likely to develop the disease and the disease becomes more severe.

The progenitor

The single-celled organism Babesia is ingested via the tick. The protozoan uses both the tick and its host (animal or human bitten by a tick) to reproduce. In the host, the protozoa has invaded the red blood cells, in which the protozoa have multiplied asexually. The host is bitten by the tick and it sucks the infected red blood cells. Sexual reproduction takes place in the tick, during which protozoa are formed in the salivary gland of the tick. The transfer of the Babesia probably takes place 2 to 5 days after attachment.

Risk factors in humans

People without a spleen are more at risk of becoming infected. In addition, the elderly, people who use corticosteroids or people who are HIV infected are at greater risk. The disease can also be spread through a blood transfusion. Only in this way can the disease be transmitted from person to person. There is no increased risk of a serious course in pregnant women. People who are missing their spleen are advised not to work in an environment where they can contract tick bites, for example in livestock farming or work in nature such as a forester or a hunter.

The spleen

The organ the spleen ensures that the infected red blood cells are purified. It is part of the lymphatic system, but is absorbed into the bloodstream. You could think of it as a lymph node in the blood. The spleen also contains a reservoir of blood. Because it is linked to the bloodstream, it contributes to the removal of waste products from the blood. If the spleen is removed, the immune system provides less protection.


Due to the risks of a serious outcome, it is important for both humans and animals that medical help is sought quickly. Treatment can be done orally or via a transfusion. Sometimes the combination of atovaquone/azithromycin is prescribed, which kills the protozoa. If the patient is treated quickly, he or she can make a complete recovery.

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