Dermacentor tick exposure risk assessment and host variability on four types of recreational trails

Dermacentor variabilis and D. andersoni are known vectors of Rickettsia rickettsia and Francisella tularensis, the agents for Rocky Mountain spotted fever and tularemia, respectively. Although much research has focused on understanding disease host reservoirs, and transmission cycles, the public health response has mostly come in the form of public education on personal tick-bite prevention measures. Thus, citizens must be properly informed of the risks when visiting recreation areas, such as our study location, Turnbull National Wildlife Refuge (TNWR), where Dermacentor ticks are native. To determine exposure risk at TNWR four trail types were chosen with three sites on each trail and three transects of 100m on each site. The four trail types were: gravel roadway, gravel walking trail, dirt hiking trail, and wildlife trail with little human access. Host variation was determined from captured ticks using PCR of the remnant blood-meals. Past studies have mostly considered tick densities in the narrow area along the trail edge. In order to determine the magnitude of expected exposure at a range of distances from the trail, questing tick abundance was quantified at the edge, 1 m from the trail, and 7 m from the trail. We found significantly more ticks along the trail edge relative to at a distance, and at gravel walking trail relative to the wildlife trail, dirt hiking trail, and gravel roadway. Our results allow visitors and managers to make informed decisions about the relative risk of tick exposure, and provide information on host variation, associated with different trail types.