15-year Borreliaprevalence and species distribution monitoring in Ixodes ricinus/inopinatuspopulations in the city of Hanover, Germany

Lyme borreliosis, caused by Borrelia burgdorferisensu lato (s.l.) spirochaetes, is the most common tick-borne disease (TBD) in the Northern Hemisphere. Rising incidences indicate that its epidemiology may be affected by global changes. Therefore, the current study aimed to assess changes in tick infection rates with Borreliaspp. over a 15-year monitoring period in the city of Hanover, Germany, as a follow-up to previous prevalence studies (years 2005, 2010 and 2015). To assess the epidemiological risk, ticks of the Ixodes ricinus/inopinatus-complex were sampled from April to October 2020 by the flagging method at 10 frequently visited recreation areas in Hanover. Analysis by quantitative real-time PCR of 2100 individual ticks revealed an overall Borreliaprevalence of 25.5% (535/2100). Regarding different tick developmental stages, nymphs showed a significantly lower Borreliaprevalence (18.4% [193/1050]) than adult ticks (32.6% [342/1050]). Comparison with previous years revealed a stable total Borreliaprevalence along with consistent infection rates in the different developmental stages over the 15-year monitoring period. Borreliaspecies differentiation by Reverse Line Blot was successful in 67.3% of positive ticks collected in 2020, with B. afzeliibeing the dominating species (59.2% of the differentiated infections), besides B. burgdorferisensu stricto (s.s.), B. garinii, B. valaisiana, B. spielmanii, B. bavariensisand B. bissettiaeand the relapsing fever spirochaete B. miyamotoi. Additionally, the proportion of infections attributed to B. afzeliishowed a significant increase in 2020 compared to 2005 and 2015 (59.2% vs.37.6% and 32.0% of successfully differentiated infections, respectively). Coinfections with Anaplasma phagocytophilumand Rickettsiaspp. stayed stable comparing 2020 with previous years. Therefore, although changes in the Borreliaprevalence in questing ticks were not observed throughout the 15-year monitoring period, shifts in Borreliaspecies distribution may alter the epidemiological risk.