Clinical manifestations and antibody prevalence of Lyme borreliosis and tick-borne encephalitis in Sweden: a study in five endemic areas close to Stockholm.

Five populations, including 903 individuals living in 5 different areas close to Stockholm, were studied with regard to clinical manifestations and antibody prevalence of Lyme borreliosis (LB) and tick-borne encephalitis (TBE). The study areas involved 4 groups of islands in the Baltic Sea and 1 island in Lake Mälaren. Serum samples from each individual were tested for antibody activity to Borrelia burgdorferi using a sonicated whole spirochete antigen in an ELISA, and to TBE-virus (TBEV) by ELISA and haemagglutination inhibition. A history of LB was reported by 1-21% and antibodies to Borrelia burgdorferi were found in 7-29% of the participants from the various areas. An increasing seroprevalence with age was seen. In sera from 3 different control groups, including 502 individuals living in non-endemic areas, antibodies to Borrelia burgdorferi were detected in 1-2% and from 1 control group including 150 individuals living in the city of Stockholm, in 9%. A history of TBE was reported by 0-6% of the individuals and in non-immunized individuals seropositivity was seen in 4-22%, depending on the area investigated. No antibody activity to TBEV could be detected in sera from persons in the 3 control groups living in non-endemic areas, whereas 5% of the controls from Stockholm were found to be positive. The prevalence rates of antibodies to TBEV in persons vaccinated against TBE were 40%, 53% and 79% after 1, 2 and 3 injections, respectively.