Prevalence of Borrelia burgdorferi sensu stricto, Borrelia afzelii, Borrelia garinii, and Borrelia valaisiana in Ixodes ricinus ticks from the northwest of Norway

Abstract

Objectives: Over a 3-y period, Ixodes ricinus ticks were randomly collected to study the prevalence of 4 Borrelia species: B. burgdorferi sensu stricto, B. afzelii, B. garinii and B. valaisiana. While B. burgdorferi s. s., B. afzelii, and B. garinii have been associated with human borreliosis in Norway for several years, B. valaisiana was reported in a Norwegian tick for the first time in 2010.

Methods: A real-time polymerase chain reaction (qPCR) was developed as an easy-to-use method, with high sensitivity and specificity, to detect and genospecies-type B. burgdorferi s. s., B. afzelii, B. garinii, and B. valaisiana in I. ricinus ticks. A combination of species-specific primers and TaqMan MGB probes labelled with fluorescents with different emission spectra, ensured a highly specific method with the potential to detect more than 1 genospecies in 1 run. Sequencing of the housekeeping gene recG from 48 Borrelia-positive samples was used to confirm specificity. Denaturing gradient gel electrophoresis profiling of tick-borne bacteria was used to help optimize the assay sensitivity.

Results: The qPCR assay was applied to analyze 1808 I. ricinus ticks collected in the field, which resulted in an overall infection rate of 14.8%, 18.7%, and 14.3% in 2010, 2011, and 2012, respectively. The majority of the Borrelia-infected ticks were infected with B. afzelii.

Conclusions: The overall infection rate is somewhat lower than that reported in the most recent study of the infection rate in southern Norway in 2010, and this study indicates that the infection rate varies from one year to another.