Prevalence and genotypes of Borrelia burgdorferi sensu lato infection in Ixodes ricinus ticks in southern Norway

Abstract

From April to October 2007, host-seeking Ixodes ricinus ticks were collected from 4 locations in southern Norway: Farsund, Mandal, Søgne and Tromøy. Two hundred and ten larvae, 1130 nymphs and 449 adults were investigated for infection with Borrelia burgdorferi sensu lato (s.l.) by real-time polymerase chain reaction (PCR) amplification of the 16S rRNA gene. The total percentage of B. burgdorferi s.l. in nymphal and adult ticks was determined to be 31.3% in Farsund, 25.2% in Mandal, 22.3% in Søgne and 22.1% in Tromøy. Larvae were pooled in groups of 10 before analysis, and Borrelia infection was detected in 1 of the 21 larvae pools. B. burgdorferi s.l. were genotyped by melting curve analysis after real-time PCR amplification of the hbb gene, or by direct sequencing of the PCR amplicon generated from the rrs (16S)–rrl (23S) intergenetic spacer. The most prevalent B. burgdorferi genospecies identified were B. afzelii (61.6%), followed by B. garinii (23.4%) and B. burgdorferi sensu stricto (10.6%). B. valaisiana (4.5%) was identified in Norwegian ticks for the first time. Mixed infections were observed in 0.3% of the infected ticks. A higher prevalence of B. burgdorferi s.l. was found in the present study than what has been reported in previous Nordic studies.

Acknowledgements

This work was supported by The Competence Development Fund of Southern Norway and The Norwegian Ministry of Education and Research. We are grateful to Sven Bergström and his group at the Department of Molecular Biology, Umeå University, and Eva Ruzic-Sabljic and her group at the Institute of Microbiology and Immunology, Faculty of Medicine, University of Ljubljana, for their great hospitality, and for providing Borrelia strains. We also acknowledge the advice of Reidar Mehl at the Norwegian Institute of Public Health in the selection of collection sites and the method of collection. Finally, we thank the 2 anonymous reviewers for valuable comments.

Declaration of interest: No conflicts of interest exist.