The efficacy of the mitochondrially encoded cytochrome b gene as a molecular marker for the discrimination of the reservoir host species of the Lyme borreliosis spirochete, Borrelia burgdorferi sensu lato (s.l.), in its European vector Ixodes ricinus (Acari: Ixodidae) was determined. Degenerate PCR primers were designed which amplified orthologous regions of the cytochrome b gene in several animal species which act as B. burgdorferi s.l. reservoirs and hosts for I. ricinus. PCR products were amplified and characterized by hybridization and restriction fragment length polymorphism analysis. Restriction fragment length polymorphism analysis of a 638-bp PCR product with HaeIII and DdeI revealed unique restriction fragment profiles, which allowed the taxonomic identification of animals to the genus level. A system was devised for the detection of the larval host blood meal from the remnants in unfed nymphal I. ricinus ticks by nested PCR amplification. An inverse correlation was demonstrated between amplicon size and successful PCR amplification of host DNA from the nymphal stage of the tick. The stability of the cytochrome b product as a marker for the identification of the larval host species in the nymphal instar was demonstrated up to 200 days after larval ingestion (approximately 165 days after molting) by reverse line blotting with a host-specific probe. This assay has the potential for the determination of the reservoir hosts of B. burgdorferi s.l. by using extracts from the same individual ticks for both the identification of the host species and the detection of the Lyme borreliosis spirochete.
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