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The aim of this study was to determine the occurrence of tick-borne pathogens of medical importance in questing ticks collected from five recreationally used islands along the Norwegian coastline. Furthermore, since coinfection may affect the disease severity, this study aimed to determine the extent of coinfection in individual ticks or co-localization of tick-borne pathogens. In all, 4158 questing Ixodes ricinusticks were analyzed. For detection of tick-borne encephalitis virus (TBEV), nymphs (3690) were analyzed in pools of ten. To detect Borrelia burgdorferisensu lato, B. miyamotoi, Anaplasma phagocytophilumand CandidatusNeoehrlichia mikurensis, 468 nymphs were analyzed individually. A total of five nymph pools was infected with TBEV, giving an overall prevalence of 0.14%. In the individually analyzed ticks, B. burgdorferis. l. (15.6%), CandidatusN. mikurensis (11%), A. phagocytophilum(1.4%) and B. miyamotoi(0.9%) were detected. Coinfection was found in 3.3% of the ticks, and the only dual infection observed was with B. afzeliiand CandidatusN. mikurensis. This association was significantly higher than what would occur by random chance.

Ticks are important vectors of disease for both humans and animals. In Europe, Lyme borreliosis is the most abundant tick-borne human disease, whereas anaplasmosis, or tick-borne fever, is the most widespread tick-borne infection in domestic animals. However, knowledge about the prevalence of the causative disease agents in questing ticks in the northern range of their distribution in Norway is missing. Ixodes ricinusticks were therefore collected by flagging vegetation in Brønnøysund, an area near the Arctic Circle in Norway where ticks have been abundant for decades. Ticks were analysed for infection with Borrelia burgdorferisensu lato and Anaplasma phagocytophilumby real-time PCR amplification of the 16S rRNA gene of B. burgdorferiand the msp2gene of A. phagocytophilum. B. burgdorferis.l. were subsequently genotyped by conducting a melt curve analysis of the PCR-amplified hbbgene or by directly sequencing the PCR-amplified rrs(16S)-rrl(23S) intergenetic spacer. A. phagocytophilumwas genotyped by msp2gene sequencing. B. burgdorferis.l. isolates were detected in 11.3% (15/133) of the nymphal ticks and in 33.3% (29/87) of the adult ticks. Of the 44 Borrelia-infected ticks collected, B. afzeliiwas identified in 42 ticks (95.5%), whereas B. gariniiwas detected in only 2 ticks (4.5%). A. phagocytophilumwas detected in 0.8% of nymphal ticks (1/133) and in 4.6% of adult ticks (4/87). Mixed infections of more than one B. burgdorferigenospecies were not observed. One adult tick was co-infected with B. afzeliiand A. phagocytophilum.