PREVALENCE OF BORRELIA-BURGDORFERI IN SELECTED TICK POPULATIONS IN FINLAND

The purpose of the studies was to determine the prevalence of Borrelia burgdorferi sensu late in selected populations of Ixodes ricinus in F inland and to secure strains of the spirochete for further characteriz ation. 1,210 Ixodes ricinus ticks (399 females, 419 males and 392 nymp hs) were collected during June to August 1992 by Ragging from 8 sites in 3 regions. The frequency of B. burgdorferi infection was determined by isolation in BSK II medium. The species identity of most of the is olates was confirmed with the immunofluorescence method. 67 B. burgdor feri strains were isolated from 8 sites; the prevalence ranged from 2. 8% to 7.9%. The overall isolation percentage for adult male ticks was 6.4% (7.5% for females, 5.3% for males); for nymphs, 3.8%. No statisti cally significant association of the prevalence was observed with eith er pasture or off-pasture habitats nor with specific geographic region /regions. Prevalence figures were roughly of the same magnitude in are as and parts of the country known to differ in their incidence of huma n borreliosis. An additional 294 ticks, mainly engorged females, were collected from places outside the main study sites. Of the 7 positive ticks 3 were engorged females, originating from a cow, a dog and a cat , respectively. The results in general demonstrate that tick populatio ns in various parts of Finland quite commonly harbour B. burgdorferi.