[Natural epidemiology of Lyme borreliosis with reference to clustered incidence of illnesses in the suburbs of a North Baden community].

Human infection with Borrelia burgdorferi, the causative agent of Lyme disease, is unusually common in the "Scheelkopf" area of the town Bruchsal in north Baden (Germany), a situation which has led to considerable publicity and public concern. This study was carried out in order to clarify this situation by determining the prevalence of B. burgdorferi in both the free-living tick populations (Ixodes ricinus) and the rodent population from the "Scheelkopf" as well as from surrounding control areas. The polymerase chain reaction (PCR) was used to determine the presence of infection in whole tick preparations and in mouse bladders. The prevalence of B. burgdorferi in freeland ticks ranged from 19% to 44% and in mice from 6% to 29% depending on the area studied. The "Scheelkopf", with prevalences for ticks and mice of 33% and 10% respectively, was not significantly different from the control areas. Our results indicate that there is a high risk of human infection throughout the study area. This is probably related to the intensive use of the area for gardens and the related recreational behaviour of the human population in conjunction with the high rate of infection prevailing in I. ricinus.