Tick-borne encephalitis

Tick-borne encephalitis is an inflammation of the brain or meninges that is caused by the tick-borne encephalitis virus (TBE virus). Infected ticks transmit the TBE virus to other animals, and sometimes to human beings.

What is tick-borne encephalitis?

Tick-borne encephalitis is an inflammation of the brain or meninges that is caused by the tick-borne encephalitis virus (TBE virus). Until recently, the virus only occurred abroad, but in the spring of 2016, there were signs that in the Netherlands deer had been infected by the virus and the virus was found in ticks in the Netherlands. There is one known case of a person having been infected by the virus in the Netherlands. The virus is transmitted by tick bites. 

Symptoms

There are several types of TBE virus. In general, all  types cause infections with a similar disease progression. The TBE virus which occurs in Far-Eastern Russia often causes more serious disease. The risk of an infection after a tick bite is very small, because only very few ticks are infected with the TBE virus. People who have been infected after a tick bite usually do not present any clinical manifestations. Otherwise the disease often comes in 2 phases. The incubation period of 7-14 days is followed by a phase  in which a patient suffers from fever, fatigue, general malaise and headache. This usually lasts 2-7 days and is followed by an asymptomatic period of approximately 1 week, In the second phase of the disease the patient has symptoms such as severe headache and encephalitis, meningitis or meningoencephalitis. In this stage the patient needs to be admitted to a hospital. Some patients will develop unresolved neurological aspects. Approximately 1-2% do not survive. There is no specific medication to treat tick-borne encephalitis. 

Infection and prevention

The TBE virus is transmitted by infected ticks to humans . There is a vaccine that gives 95% protection. People who stay for a long period in areas where tick-borne encephalitis occurs, can have themselves vaccinated; this is recommended for example in parts of Central and Eastern Europe. For information about countries where vaccination is recommend,  we refer to the website of the National Coordination of Advice for Travellers (Landelijke Coördinatie Reizigersadvisering). For the time being, there is no reason to vaccinate people in the Netherlands.

Removing  ticks as soon as possible reduces the infection risks of viruses they may carry, such as the virus that causes Lyme disease. TBE virus, however, is transmitted shortly after the bite. So, quickly removing the tick will not always prevent infection. Tick bites can be prevented by wearing protective clothing and by  using  repellents that contain DEET on exposed skin. Repellants do not protect 100%, so tick bite checks remain a necessity after being outdoor/in nature. TBE virus is rarely found in farm animals, such as sheep, goats and cows. The virus is than excreted in milk. As a result people could be infected by drinking unpasteurized infected milk or eating cheese made from infected milk.

Where does the tick-borne encephalitis virus occur?

Tick-borne encephalitis virus occurs in parts of Europe, Russia and Central Asia. In  Europe there are approximately 2000 patients with TBE per year and in Russia  approximately 10,000. In the Netherlands, the TBE virus has been found in ticks in the national parks Sallandse Heuvelrug and Utrechtse Heuvelrug. RIVM investigates, in collaboration with other organisations, the spread of the TBE virus in the Netherlands and the risk of infection. 

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