Local tick populations and human disease risk along popular hiking trails in northern California after multiple weather extremes.

Abstract

This field study describes the abundance of ticks and the prevalence of tick-borne pathogens in two hiking areas, Stebbins Cold Canyon (SCC) and Skyline Wilderness Park (SKY), in northern California. These areas have experienced extreme weather events, including wildfire, drought, and heavy rainfall, which have changed the environment. Questing ticks were collected over nine months, identified to species, and screened for tick-borne pathogens using qPCR. Four hundred and fifty-nine ticks were collected, including 54 adults from SCC and 405 from SKY, consisting of 279 (68.9%) larvae, 2 (0.5%) nymphs, and 124 (30.6%) adults. At SCC, Ixodes pacificus and Dermacentor occidentalis accounted for 92.6% (50/54) and 7.4% (4/54), respectively. At SKY, I. pacificus (16.8%, 68/405), D. occidentalis (12.3%, 50/405), D. similis (0.7%, 3/405), and D. albipictus (70.4%, 285/405) were collected. Overall, the prevalence of tick-borne pathogens was low in the collected ticks. Borrelia burgdorferi sl (0.8%, 1/121) and Rickettsia rhipicephali (1.7%, 2/121) were found at SKY. Rickettsia tillamookensis was identified at SCC and SKY with a prevalence of 3.7% (2/54) and 1.7% (2/121), respectively. Babesia duncani was identified in 3.7% (2/54) and 1.2% (5/405) of ticks at SCC and SKY, respectively. These findings suggest that multiple tick species can withstand extreme weather events, providing further data regarding the effects of weather extremes and climate change on tick populations and pathogen prevalence. This study is one of the first to report B. duncani in I. pacificus ticks in California, particularly in Solano County.