Seasonal patterns and spatial variation of Borrelia burgdorferi (sensu lato) infections in Ixodes ricinus in the Netherlands

Abstract

Background The incidence of Lyme borreliosis varies over time and space through as yet incompletely understood mechanisms. In Europe, Lyme borreliosis is caused by infection with a Borrelia burgdorferi (s.l.) genospecies, which is primarily transmitted by a bite of Ixodes ricinus nymphs. The aim of this study was to investigate the spatial and temporal variation in nymphal infection prevalence of B. burgdorferi (s.l.) (NIP), density of questing nymphs (DON) and the resulting density of infected nymphs (DIN). Methods We investigated the infection rates in I. ricinus nymphs that were collected monthly between 2009 and 2016 in 12 locations in the Netherlands. Using generalized linear mixed models, we explored how the NIP, DON and DIN varied during the seasons, between years and between locations. We also determined the genospecies of the Borrelia infections and investigated whether the genospecies composition differed between locations. Results The overall NIP was 14.7%. A seasonal pattern in infection prevalence was observed, with higher estimated prevalences in the summer than in the spring and autumn. This, combined with higher nymphal densities in summer, resulted in a pronounced summer peak in the estimated DIN. Over the 7.5-year study period, a significant decrease in infection prevalence was found, as well as a significant increase in nymphal density. These two effects appear to cancel each other out; the density of infected nymphs, which is the product of NIP × DON, showed no significant trend over years. Mean infection prevalence (NIP, averaged over all years and all months) varied considerably between locations, ranging from 5 to 26%. Borrelia genospecies composition differed between locations: in some locations almost all infections consisted of B. afzelii, whereas other locations had more diverse genospecies compositions. Conclusion In the Netherlands, the summer peak in DIN is a result of peaks in both NIP and DON. No significant trend in DIN was observed over the years of the study, and variations in DIN between locations were mostly a result of the variation in DON. There were considerable differences in acarological risk between areas in terms of infection prevalence and densities of ticks as well as in Borrelia genospecies composition.

Bacterial Agents Detected in 418 Ticks Removed from Humans during 2014–2021, France

“…Ixodes spp. tick bites can occur throughout the year but have a higher prevalence in summer when tick populations, especially biting nymphs, are at their peak, which is also associated with the highest occurrence of Lyme disease (23). We observed that I. ricinus ticks were frequently infected by Borrelia sp.…”

Monitoring of ticks and their pathogens from companion animals obtained by the “tekenscanner” application in The Netherlands

“…Infection with B. burgdorferi in dogs and cats leads to seroconversion, but direct relation with the disease development is still contentious (Littman et al 2018). Humans are mostly bitten by I. ricinus nymphs (Hartemink et al 2021), therefore the infection of B. burgdorferi s.l. in nymphs (4.1%) is of medical importance.…”

Anti‐tick and pathogen transmission blocking vaccines

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