TBEV is transmitted by Ixodes ricinus ticks. TBE is restricted to the archipelago and Lake M laren on the east coast close to Stockholm. Between 30 and 100 cases are diagnosed every year. Inkoo virus , a California encephalitis group virus, has been isolated from mosquitoes in Sweden. The antibody prevalence to Inkoo virus is very high in a normal population in northern Sweden, but no disease has as yet been associated with this virus in Sweden.
Dengue fever is the single most common imported vector borne viral disease in Sweden.
During the same season, one Swedish tourist visiting Cyprus was also diagnosed. In 1986-1989 a total of 37 cases of SF occurred among Swedish patients. One patient was diagnosed with a Naples virus infection, one with Toscana virus and the remaining 35 with Sicilian virus infections. After travelling in sub-Saharan Africa, an area where sporadic cases of Marburg virus infection are known to occur, a young Swedish man presented in 1991 with a classical picture of severe Viral hemorrhagic fever , complicated by disseminated intravascular coagulation and septicaemia. Serum samples examined by electron microscopy revealed particles of a size compatible with filovirions.