Tick bite risk resulting from spatially heterogeneous hazard, exposure and coping capacity

Abstract

Tick-borne diseases have long been mainly associated with forests, the primary habitat for Ixodes ricinus, where they are mostly found. However, increasing evidence shows that humans also often get bitten in gardens, parks and other habitats generally associated with lower vegetation and tick density. Therefore, to understand the risk of infection from a tick bite and thus of potential subsequent infection, it is necessary to separate the factors of risk: hazard and vulnerability, here detailed as exposure and coping capacity, and to examine their spatial heterogeneity. This paper proposes a spatially explicit model for human movement through the entire landscape and forest visits to investigate the three components of risk. The population and its movements are set spatially in three study case landscapes extracted from Wallonia, south Belgium. Parameters that are challenging to estimate, such as the probability of a person getting bitten in various environments and the probability of inspecting one’s body to remove ticks, are analyzed in a wide range of combinations. Results show that, while bites are densest in the forest, they happen across the landscape at levels comparable when summed. When coping capacity is modified, as it could be through raising awareness and improving uptake of protective measures, the most at-risk group can change, and the riskier landscape can become the periurban or the rural landscape. This model offers a platform to investigate the respective contributions of hazard, exposure, and people’s capacity to cope with the hazard. It would benefit from empirical input parameters measured more specifically for its purpose.