Danger on the track? Tick densities near recreation infrastructures in forests

Abstract

The risk of tick-borne disease in humans depends on the exposure to pathogen-infected ticks, which in turn is driven by local tick population densities, pathogen prevalence and human activity. Variation in tick densities and pathogen prevalence between green spaces differing in habitat characteristics, location and geography has been well documented. In contrast, variation within green spaces, although vital for management and prevention of disease risk, remains poorly understood. Studying this variation may lead to a better understanding of the drivers of small-scale tick distribution and reveal priority locations for tick management. We sampled ticks within green spaces at three location types representing different green space infrastructures and levels of human activity: (1) a structural element (e.g. bench); (2) the ecotone 40 m further along the adjacent trail and; (3) the interior of the associated forest stand, 20 m perpendicular to the trail, between (1) and (2). Drag sampling took place in 2018 and 2019 at 36 locations in 10 green spaces located in the Campine region of Flanders, Belgium. The density of questing nymphs (DON) was lowest at structural elements and slightly higher adjacent to trails. The highest tick densities were recorded in the forest interior. DON was higher in deciduous than in coniferous forests as well as in stands with a more developed shrub layer. This was true for all location types, as we observed a strong correlation of DON between location types within forest stands. This enables the prediction of DON within forest stands, thus enabling the prediction of DON near infrastructure based on the associated forest stand characteristics. Prevention and management efforts should be focused on infrastructure in or adjacent to deciduous, structure-rich forest stands, although large variation in DON at all location types indicates overall, factual risk while using green space infrastructure.