Density of deer in relation to the prevalence of Borrelia burgdorferi sl in Ixodes ricinus nymphs in Rambouillet forest, France

The Rambouillet Forest, a Lyme disease-endemic area near Paris, France, was surveyed from September 1994 to October 1995 to determine the risk periods and zones for humans. Firstly, during the period of Ixodes ricinus activit y, abundance of nymphs is greater in spring than in autumn. Secondly, we ob served significant variation in nymphal abundance between zones according t o the density of cervids. The polymerase chain reaction (PCR) was used to d etect DNA of Borrelia burgdorferi sensu late in 461 unfed nymphs. DNA was d etected in 38 nymphs (8.2%). By genospecific PCR based on the OspA gene, we detected the three pathogenic spirochetes with occurrences of 10.3, 31.1 a nd 58.6 for B. burgdorferi s.s., Borrelia garinii and Borrelia afzelii, res pectively, indicating that B. afzelii is probably the main Borrelia species in the Rambouillet Forest. Finally, 11.5% of positive nymphs exhibited a d ouble infection. Infection rates of I. ricinus nymphs by B. borgdorferi s.l . were not significantly different throughout the year for a given area, in dicating that the risk periods of acquiring Lyme disease are mainly linked to nymph activity and correspond to spring and autumn. Likewise infection r ates of nymphs were not significantly different between zones with a high d ensity of deer (more than 100 animals per 100 ha) and zones with lower deer density (less than 20 animals per 100 ha). In addition to the role of deer as an amplifier of tick populations, these data indicate that zones with a high density of cervids should be considered as higher risk areas. Expl Ap pl Acarol 23:267-275 (C) 1999 Kluwer Academic Publishers.