Prevalence and Diversity of Borrelia Species in Ticks That Have Bitten Humans in Sweden

Members of the genus Borrelia are among the most common infectious agents causing tick-borne disease in humans worldwide. Here, we developed a Light Upon eXtension (LUX) real-time PCR assay that can detect and quantify Borrelia species in ticks that have fed on humans, and we applied the assay to 399 such ticks. Borrelia PCR-positive ticks were identified to species level by sequencing the products of conventional PCR performed using Borrelia group-specific primers. There was a 19% prevalence of Borrelia spp. in the detached ticks, and the number of spirochetes per Borrelia PCR-positive tick ranged from 2.0 × 10 2 to 4.9 × 10 5 , with a median of 7.8 × 10 3 spirochetes. Adult ticks had a significantly larger number of spirochetes, with a median of 8.4 × 10 4 compared to the median of nymphs of 4.4 × 10 4 . Adult ticks also exhibited a higher prevalence of Borrelia (33%) than nymphs (14%). Among the identified species, Borrelia afzelii was found to predominate (61%) and was followed by B . garinii (23%), B . valaisiana (13%), B . burgdorferi sensu stricto (1%), B . lusitaniae (1%), and B . miyamotoi -like (1%). Also, 3% of the ticks were coinfected with multiple strains of B. afzelii . Notably, this is the first report of B. lusitaniae being detected in ticks in Sweden. Our LUX real-time PCR assay proved to be more sensitive than a corresponding TaqMan assay. In conclusion, the novel LUX real-time PCR method is a rapid and sensitive tool for detection and quantification of Borrelia spp. in ticks.