The prevalence of Borrelia burgdorferi sensu lato in questing Ixodes ricinus ticks in Norway

Abstract

Norway represents the northern limit in the geographical distribution of Ixodes ricinus ticks in Europe. During the last decade an expansion of the range of this tick further north and at higher altitudes has been detected. This could affect the spread of Borre­lia burgdorferi sensu lato pathogens in new territories and increase the risk of human infection in the country. The aim of the present study was to determine the prevalence of B. burgdorferi s.l. in I. ricinus ticks in different localities of Norway. Ticks were collected in 24 locations from northwest to southeast Norway during spring– summer 2004 and 2006–2008. We used fla gene as a target for amplification of spirochete DNA. Multiplex PCR based on ospA gene of B. burgdorferi s.l. was used for species identification. The heterogeneity of B. garinii strains was investigated using ospA-based sequencing analysis. B. burgdorferi s.l. was detected in 171 (7.2%) out of 2360 I. ricinus ticks analyzed. The infection rate varied from zero to 32% in the investigated locations. Infection rate in adults (11.9%) was significantly higher than in nymphs (4.7%). The overall infection rate in ticks from western Norway (4.0%) was significantly lower than in those from southern Norway (10%). Four B. burgdorferi  s.l. genospecies were identified, and the most common was B. afzelii (71.9.0%), followed by B. garinii (12.9%), B. burgdorferi s.s. (7%) and B. valaisiana (1.2%). A total of eight (4.8%) of the infected ticks harboured mixed infections. Phylogenetic relationship between B. garinii strains and their cor­respondence to OspA serotype types was compared with the sequences registered in GenBank database. Five genotypes of B. garinii derived from ticks were identified. The most frequent was OspA type 6.