SEASONAL PREVALENCE OF BORRELIA-BURGDORFERI IN IXODES-RICINUS IN DIFFERENT VEGETATION TYPES IN SWEDEN

The aim of this investigation was to estimate the seasonal risk of con tracting human Lyme disease in different vegetation types in southern Sweden. Host-seeking Ixodes ricinus ticks (Acari: Ixodidae) were colle cted with standardized methods during May-September 1988 and March-Oct ober 1989 at 10 different sampling sites. Tick abundance was greatest during May-June and August-September. Prevalence of Borrelia burgdorfe ri infection of the ticks was assessed by phase-contrast microscopy co mplemented by immunology. Spirochetal infection of tick larvae was not detected. The prevalence of infection among nymphal ticks differed si gnificantly between years and between sampling sites. Infection preval ence was greater in adult females than in nymphs, but was similar in f emale and male ticks. Among all vegetation types studied, the greatest Lyme disease risk was deemed to be from I. ricinus nymphs during May and September in mixed forest vegetation.