Tick community composition and Lyme infection prevalence of Western Black-Legged Ticks (Ixodes pacificus) in coastal and inland southern California

Background/Question/Methods

Ticks are vectors of numerous diseases including Lyme disease, Rocky Mountain spotted fever and Babesiosis which, according to the Centers for Disease Control and Prevention, result in almost 30,000 cases of human disease annually in the US alone. Lyme disease, the most common vector-borne disease in the US, occurs most frequently in the northeast and research efforts have mirrored this pattern. As a result, very little is known about the tick community on the West Coast, which makes it difficult to forecast future disease risk under changing land use and climate. Here we characterize the tick community of both questing and feeding ticks as well as infection prevalence with the causative agent of Lyme disease, Borrelia burgdorferi, of the Western Black-Legged Tick (Ixodes pacificus). Community sampling and infection prevalence estimates are made in both coastal and inland sites in Southern California, which differ in abiotic conditions and host community. Tick communities were sampled using weekly drag sampling to assess questing ticks and by collecting feeding ticks from small and large mammal trapping. PCR was used to quantify Lyme disease infection prevalence. Our data provide some of the most refined records of tick community composition and Lyme prevalence in Southern California.

Results/Conclusions

We find a strong seasonal pattern to both tick abundance and diversity with mid-spring having over four times the abundance and a higher diversity of both questing and feeding ticks compared to mid-summer. Questing ticks were found to clump with conspecifics both at microscales (i.e. locations within a drag sample) and at temporal scales (i.e. sampling date). Additionally, we found consistent differences in the questing tick community between coastal and inland sampling sites with inland sites having a higher abundance of ticks in general and of Black-Legged Ticks specifically, during most of the year. This result may be due to differences in climate or in host community composition. In both sites and throughout the year, the abundance of Black-Legged Ticks was low relative to other species in the tick community. Mammal samples reflected the composition and seasonal patterns of questing ticks.