IXODES-RICINUS IMMATURES ON BIRDS IN A FOCUS OF LYME BORRELIOSIS

The infestation of birds by immature Ixodes ricinus was studied during 6 months in a Swiss woodland, where Lyme borreliosis is endemic. Thir teen passerine species were found to be parasitized by I. ricinus suba dults and specially Turdus merula, T. philomelos and Erithacus rebecul a. Overall, 300 larvae and 162 nymphs were collected on 95 avian hosts . Prevalence of infestation of nymphs on birds was higher in spring; l arvae peaked in summer. The infection of birds by Borrelia burgdorferi was also studied using blood cultivation and examinations of ticks. M otionless spirochetes were isolated from two E. rubecula. Infected tic ks were removed from five species of passerines, and mainly three spec ies of Turdidae (T. merula, T. philomelos and E. rubecula). Infection rate of larvae and nymphs by spirochetes averaged 16.3% and 21.7%, res pectively. These percentages, compared to the infection rate of questi ng ticks collected through dragging, suggest that some Turdidae may pl ay a role as amplifying hosts for spirochetes in the focus.