Occurrence of different genospecies of Borrelia burgdorferi sensu lato in ixodid ticks of Valais, Switzerland.

A total of 825 adult ticks (727 Ixodes ricinus, 72 Dermacentor marginatus and 26 Haemaphysalis punctata) was collected from vegetation in Valais (Switzerland) in 1987 to 1992. They were examined for the presence of Borrelia burgdorferi sensu lato, the etiologic agent of Lyme borreliosis. B. burgdorferi sensu lato was detected by indirect immunofluorescence assay, dark field microscopy and/or culture in 221 out of 727 I. ricinus (30.4%) and none in the other two species. From these 221 infected ticks we obtained 50 isolates. Indirect immunofluorescence assay and culture were used for all ticks but dark field examination has also been performed and compared to the two above mentioned methods for 231 I. ricinus. Indirect immunofluorescence assay and culture were used for all ticks but dark field examination has also been performed and compared to the two above mentioned methods for 231 I. ricinus. Indirect immunofluorescence was found the most efficient method for the detection of Borrelia in ticks with 54 positive out of 231, followed by dark field examination with 35 positive and culture with 12 isolates. We found no site free of Borrelia where I. ricinus is present. The rate of infection varied from 9.7 to 47.5%, as detected by the addition of the three methods. Typing of the 50 isolates revealed also a nonhomogeneous distribution of the Borrelia species. Based on the electrophoretic mobility of the OspA and B and immunostaining with species specific monoclonal antibodies (H3TS for B. burgdorferi sensu stricto, D6 for B. garinii and J8.3 for B. afzelii) 4 groups could be observed. Half of the isolates (n = 26) were typed as B. burgdorferi sensu stricto, 19 as B. garinii, 3 as B. afzelii and 2 as group VS116. This forth group formed of two isolates from one location is genetically distinct from the 3 former species described in Europe so far. The Borreliae of this group are unreactive with any of the three monoclonal antibodies used.