REVIEW – April 2007

Tick – born encephalitis – a common viral infectious disease involving the nervous system


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Tick – born encephalitis (TBE) is an inflammatory disease which is caused by flaviviruses. TBE is one of the most common viral infections involving the nervous system. The viruses are transmitted through bites of infected ticks or drinking fresh milk of infected cows or goats. In Estonia the incidence of TBE was 12 to 20 cases per 100 000 population in the period 1999 to 2006. This is higher than in Western Europe and Scandinavia and may be associated with the discontinuation of large-scale agriculture after the collapse of the previous political system in 1991. A total of 151 TBE cases were diagnosed and treated in the department of neurology of the University of Tartu in 1999 – 2006 with a mean patient age of 49.3 years (17 – 82 yrs). The criterion for diagnosing TBE is presence of positive IgM antibodies in the cerebrospinal fluid and in the blood serum. The most common clinical form was aseptic meningitis. In 2004 four cases and in 2006 two cases were diagnosed as meningoencephalitis. Encephalomyelitis was diagnosed once per year in 2004, 2005 and 2006. No cases of  polyradiculoneuropathia caused by TBE have been diagnosed in the TU department of neurology. There have been no lethal cases. In 2006 four persons from one family were admitted in the TU department of neurology with similar symptoms of meningitis: high temperature, headache, nausea, vomiting. There had been no contact with ticks or tick bites in the past. All four persons were relatives and had drunk the same fresh unpastorized milk of their goat. They all had positive IgM antibodies of TBE in the serum and in the cerebrospinal fluid. They were diagnosed with aseptic meningitis with lymphocytic pleocytosis and symptomatic treatment was provided. Two persons improved well and two had moderate asthenia. In 2005 and 2006 the Estonian Health Inspectorate registered several cases of TBE where transmission of the virus to humans probably occurred through infected milk. The Inspectorate recommends pasteurizing milk before use. The most effective preventive activity is vaccination.