GENETIC-HETEROGENEITY OF BORRELIA-BURGDORFERI SENSU LATE IN IXODES-RICINUS TICKS COLLECTED IN BELGIUM

Borrelia burgdorferi sensu late (s.l,), the etiological agent of Lyme disease, is transmitted by the bite of Ixodes ricinus, Four hundred ei ghty-nine ticks, collected in four locations of a region of southern B elgium where Lyme disease is endemic, were examined for the presence o f the spirochete. In a PCR test with primers that recognize a chromoso mal gene of all strains, 23% of the ticks were found to be infected. T he species B, burgdorferi s,l. comprises at least three pathogenic gen omospecies, B, burgdorferi sensu stricto (s,s.), Borrelia garinii, and Borrelia afzelii, which could be distinguished in PCR tests with spec ies-specific primers that correspond to distinct plasmid sequences. B. garinii was most prevalent (53% of infected ticks), followed by B, bu rgdorferi s.s, (38%) and B. afzelii (9%). Of the infected ticks, 40% w ere infected,vith a single species, 40% were infected with two species , and 5% were infected with all three species. For 15% of the ticks, t he infecting species could not be identified. No difference in rates o f prevalence was observed among the four locations, which had similar ground covers, even though they belonged to distinct biogeographic reg ions, A greater heterogeneity of spirochetal DNA in ticks than in cult ured reference DNA was suggested by a comparison of the results of PCR s with two different sets of species-specific primer sequences.