Relationship between <i>Borrelia burgdorferi</i> sensu lato species, red squirrels (<i>Sciurus vulgaris</i>) and <i>Ixodes ricinus</i> in enzootic areas in Switzerland

The infection and reservoir status of red squirrels (<i>Sciurus vulgaris</i>) for <i>Borrelia burgdorferi</i> sensu lato were studied in Switzerland. <i>B. burgdorferi</i> sensu lato was isolated from 15 skin samples from 4/6 dead red squirrels, victims of road traffic. Isolates were identified using restriction fragment length polymorphism (RFLP): <i>B. burgdorferi</i> sensu stricto was present in 14 culture tubes containing skin samples and <i>B. afzelii</i> in two other tubes. A mixed infection was revealed in one case. A total of 227 ticks attached to squirrels were cultivated in BSKII medium and 90 isolates were obtained. Genotypic identification by RFLP showed that <i>B. afzelii</i> (59%) and <i>B. burgdorferi</i> sensu stricto (46%) dominated in ticks feeding on red squirrels. Data collected from one particular animal, highly infested with <i>Ixodes ricinus</i> and harbouring numerous <i>Borrelia</i>-infected <i>Ixodes ricinus</i> ticks, showed that transmission of <i>B. burgdorferi</i> sensu lato occurred from <i>S. vulgaris</i> to feeding ticks. More precisely, <i>B. burgdorferi</i> sensu stricto and <i>B. afzelii</i> were mainly transmitted from <i>S. vulgaris</i> to ticks. The present data emphasized the results obtained previously from small rodents and birds in Japan and in Switzerland, showing the occurrence of specific associations between host species and <i>Borrelia</i> genospecies.