POPULATION GENETIC-STRUCTURE OF IXODES-RICINUS IN SWITZERLAND FROM ALLOZYMIC DATA - NO EVIDENCE OF DIVERGENCE BETWEEN NEARBY SITES

Ixodes ricinus is a vector and reservoir of numerous infectious agents , especially Borrelia burgdorferi, the agent of Lyme disease. In Switz erland, its ecology and physiology have been well studied. Moreover, t he foci of some infectious agents transmitted by this tick are identif ied. They can display relatively to extremely small geographical size depending on the diseases considered. In order to understand how the g ene flows occur and to characterise the genetic structure of Ixodes ri cinus populations, we used an indirect method based on genetic markers : allozymes. The sampling was carried out in 5 localities. Eighteen lo ci were analysed and 2 appeared polymorphic. This shows the low allozy mic variability displayed by Ixodes ricinus. Based on these 2 loci, th e populations appeared panmictic in Switzerland. This may be explained by the wide range of vertebrate species this tick can infest, especia lly birds. However, the result is surprising if we consider the extrem e localisation of the foci of some infectious agents. We conclude that more powerful genetic markers could be used in order to better unders tand the epidemiology of tick-borne diseases in Switzerland. (C) 1997 Australian Society for Parasitology. Published by Elsevier Science Ltd .