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Tick-borne encephalitis is a viral infection of the central nervous system transmitted by tick bites, usually after travel to rural or forested areas. The disease may also be acquired by ingesting unpasteurized dairy products. Two subtypes have been identified, sometimes known as Russian spring/summer encephalitis and Central European encephalitis, but there is little difference between them. The disease is reported from Scandinavia, Western Europe, Central Europe, the former Soviet Union, and East Asia. The peak incidence is from April through August. The incubation period is usually from one to two weeks, but may vary. The disease typically begins as a flu-like illness, including fever, headache, and vomiting, followed by the development of neurologic symptoms, including neck stiffness, dizziness, tremors, drowsiness, delirium, and coma. Neurologic damage may be permanent, causing chronic headaches, difficulty concentrating, muscle weakness or loss of balance. A small percentage of cases are fatal. The disease is rarely severe in children less than four years old.
Three vaccines have been developed for tick-borne encephalitis. The first, called FSME Immun (Baxter AG), consists of inactivated, purified whole virus. The vaccine is manufactured in Austria and approved for use in a number of European countries, but is not available in the United States. In Canada, the vaccine can be obtained through the Emergency Drug Release Program at (613) 941-2108 or at the Bureau of Biologics at (613) 941-2114. A full series consists of three doses over a one-year period (at times 0, 1, and 12 months), so complete immunization is not practical for most travelers. Because a previous version of this vaccine caused high fevers in infants and young children (probably due to the absence of albumin, which has been included in the current product), FSME Immun is recommended only for those over 16 years old. Serious reactions have not been documented in older children and adults. The vaccine has been suspected of causing an exacerbation of autoimmune diseases, but a cause-and-effect relationship has not been confirmed.
Another vaccine is Encepur (Chiron Behring), which is manufactured in Germany and available in several European countries, but not North America. Like FSME Immun, the usual schedule consists of three doses over a one-year period. However, limited data indicate that an accelerated schedule, consisting of two doses separated by one week, may confer immunity in most people. A third dose should be given three-to-four weeks later, followed by a fourth dose in one year's time.
A third vaccine for tick-borne encephalitis, called Encevir, is produced in Russia. The vaccine was temporarily withdrawn in May 2010 after a number of people receiving the vaccine experienced side-effects.
There are no proven treatments for tick-borne encephalitis. Gamma globulin is sometimes used, but the effectiveness is unproven and there is evidence that it might actually lead to a more severe infection.
Tick precautions, as described elsewhere, are strongly advised for travel to rural or forested areas, especially in the spring or summer, in countries where tick-borne encephalitis is known to occur.
From the Centers for Disease Control (CDC)
A survey on cases of tick-borne encephalitis in European countries
The changing incidence of tickborne encephalitis in Europe
From the International Scientific Working Group on TBE
Map of endemic areas
Number of reported cases of TBE from various European countries and Russia
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