Despite Lyme disease being the most prevalent vector-borne disease in the US, critical gaps remain in our understanding of the vector and host interactions shaping disease dynamics. Small mammals such as deer mice (Peromyscus spp.) and dusky-footed woodrats (Neotoma fuscipes) are key hosts for Borrelia burgdorferi and can vary greatly in abundance between habitats depending on community composition. Yet, aggregation of tick vector species such as Ixodes pacificus, the western blacklegged tick, on small mammal hosts is often assumed to vary independently of host abundance. The assumption about tick aggregation is that they do not change depending on ecological factors; but rather twenty percent of the host population is burdened with eighty percent of the parasites. Tick burdens on small mammals is an important parameter in estimating and predicting Lyme disease risk as this tick-host interaction can be amplified with larger tick aggregation. This study is the first to empirically measure, I. pacificus larval burdens on high and medium reservoir competent hosts as a function of host species diversity, predator diversity and habitat patch size. We hypothesized that different factors will impact burdens on species differently. Overall, we hypothesize that as small mammal diversity and habitat patch size increases, average tick burdens would also increase. Small mammals were live trapped at oak woodland field sites that ranged in size from 11 to 2775 hectares. Attached ticks were removed then identified to species, and average burdens per trapping site were quantified.
Results/Conclusions
A total of 205 small mammals were captured, predominately N. fuscipes and Peromyscus spp. and 325 I. pacificus larval ticks were collected off these hosts. Generalized Linear Models separating N. fuscipes and Peromyscus spp. as two separate response variables resulted with different relationships impacting burdens. The average larval I. pacificus burdens on Neotoma fuscipes increase when patch size, small mammal diversity and questing I. pacificus increase; but decrease as predator diversity increases. As for Peromyscus spp., there was an increase of I. pacificus larval burdens as small mammal diversity increased; but the other factors did not significantly impact the burdens of Peromyscus spp. Further, our data demonstrates an increasing trend of tick species richness with habitat patch size. This study illustrates how habitat patch size can mediate host dynamics resulting in the impact of the distribution of pathogen vectors. These results have important implications for predicting Lyme disease prevalence, Lyme disease dynamics and ultimately human health.