Prevalence of tick-borne encephalitis and Lyme borreliosis in a defined Swedish population.

Sera from 346 individuals living on Lisö, an area south of Stockholm, endemic for tick-borne encephalitis (TBE) and Lyme borreliosis, were tested for antibody activity to TBE-virus (TBEV) and Borrelia burgdorferi, using a sonicate antigen, by haemagglutination-inhibition and ELISA, respectively. 10/346 (3%) individuals had a history of previous serologically confirmed TBE with encephalitic symptoms, and 33/346 (10%) had a history of previous erythema chronicum migrans (ECM). Four individuals (1%) had been treated for neuroborreliosis and another 4 (1%) for acrodermatitis chronica atrophicans (ACA). Antibodies to TBEV and B. burgdorferi were detected in 40/346 (12%) and 89/346 (26%) individuals, respectively. The seroprevalence of Lyme borreliosis increased with age, time spent on Lisö, and number of reported tick-bites. For TBE there was a correlation between seropositivity and time spent on Lisö only. In sera from 50 healthy blood-donors, living in a non-endemic area, no antibody activity to TBEV could be detected and only 1/50 (2%) had antibodies to borrelia. In sera from 150 age and sex matched control individuals, living in the city of Stockholm, antibody activity to TBEV and borrelia was found in 8/150 (5%) and 13/150 (9%), respectively.