Heterogeneity of Tick Abundance and Infection with Zoonotic Pathogenic Bacteria in a Belgian Peri-Urban Forest

Abstract

Background Forests are the primary habitats for Ixodes ricinus and harbor high tick populations, vectors of various pathogens. As such, they are often considered as a homogenous land cover harboring abundant tick populations. However, little is known about the heterogeneity in tick density within a peri-urban forest, where human exposure is high. The study aims to assess the micro-environmental factors that favor tick abundance and their infection with three pathogens, in a peri-urban forest. Methods Ticks were sampled 17 times in 2016 in seven locations of a peri-urban forest during the period of tick activity. Three zoonotic pathogens were screened, Borrelia burgdorferi s.l., Coxiella burnetii, and Francisella tularensis. The influences of micro-environmental factors on tick abundance and infected tick abundance were tested with multiple negative binomial generalized linear models. Results 787 nymphs and 81 adult ticks were collected., resulting in densities of 6.61 nymphs and 0.68 adults per 10 km². These densities were variable between the sites, ranging from 2.12 to 14.59 nymphs per 10m² and 0.24 to 1.29 adults per 10m². The prevalence of B. burgdorferi s.l. was estimated at 3.37%. Coxiella burnetii was detected three times (1.36%) and F. tularensis was not detected. Tick abundances were highest in deciduous forests, located in sandy and loamy-sand soils covered by dense vegetation not easily accessible to forest visitors. The temperature during the sampling also positively affected tick abundance. No variables were significant for the models for infected ticks. Conclusions Tick abundance was in the upper range of other estimated tick densities in Belgian forests. Borrelia infection prevalence was lower but the genospecies composition was similar to previous studies in Belgium. The assumption that forests are a homogenously suitable tick habitat is questioned and we underline the necessity to account for micro-environmental conditions and human exposure.