Occurrence of Borrelia burgdorferi in Ixodes ricinus in The Netherlands

In a 1989 surveillance to study the infection rate of Ixodes ricinus ticks with Borrelia burgdorferi, a total of 1838 nymphal and adult Ixodes ricinus ticks were collected from 20 locations in The Netherlands. By means of a culture method using modified Barbour-Kelly-Stoenner medium nymphs were examined in pools of 4 and adults were examined individually. With 63 out of 75 isolates propagation and serological identification were possible. All of these 63 isolates were identified as Borrelia burgdorferi by means of an indirect immunofluorescence assay. In nymphs the minimal infection rate was 2.4%. The rate of infection for adults was shown to be 14.3%. These results are in agreement with the percentages found by other investigators in West-Europe. In all locations examined Ixodes ricinus were found to be infected with Borrelia burgdorferi, although the infection rate varied. The results indicate that the infection is widespread among ticks in The Netherlands and the potential risk of acquiring Lyme borreliosis after a tick bite is serious.