Incidence of tick-bite in man in Aland Islands: reference to the spread of Lyme borreliosis.

The common tick Ixodes ricinus is a vector both for the virus of tick-borne viral encephalitis (Kumlinge disease, KD) and of Borrelia burgdorferi (Lyme borreliosis, LB). Bites of the tick are believed to be common in Aland, an island province of Finland in the Baltic Sea. KD has been seen there for many years, and cases of LB have been diagnosed lately. The purpose of this study was to find the incidence of tick-bite among the population with possible implications for the spread of LB. A questionnaire was sent to 561 persons greater than 8 years of age out of a total of 21,281 in order to record tick-bites and erythema chronicum migrans (ECM). The number of answers was 519 (92.5%). 441 persons (85%) had been bitten by ticks, 146 greater than 10 times. 14 probands had had ECM, 73 other rashes around the tick-bite. It is concluded that tick-bites are very common among the population, and thus conditions are favourable for the spread of any tick-borne infection such as LB. The number of patients with secondary or tertiary LB diagnosed in the area is presently 17. It is likely that there are many undetected cases in the area.