Associate Professor San Francisco State University San Francisco, California, United States
Abstract: The relationship between host diversity and disease risk is contentious but the dilution effect posits that species diversity has a protective effect against disease transmission. Often traditional ecological measures of diversity, such as species richness, are used to determine the presence of the dilution effect. However, these metrics of species diversity fail to consider species relatedness which has important implications for disease transmission. Phylogenetic diversity may be a better metric to evaluate the relationship between host diversity and disease transmission given that closely related species may have more similar pathogen competencies than distantly related ones. Few studies have examined the relationship between phylogenetic diversity and disease transmission, particularly in vector-borne transmission systems This study seeks to quantify phylogenetic diversity in the Lyme disease system in the western United States caused by Borrelia burgdorferi, where it is vectored by the western black-legged tick, Ixodes pacificus. We empirically measured mammalian diversity data and tick data from 14 long term field sites located across the San Francisco Bay Area from 2016-2022. Using live trapping and camera trap data, we determined several metrics of host diversity including traditional measures as well as phylogenetic diversity. Questing ticks were collected and tested for infection with Borrelia burgdorferi to determine disease risk. We used generalized linear model analyses to evaluate the ability of different diversity metrics to predict disease risk. Our results show that host diversity has important impacts on tick-borne disease risk. Rodent and wildlife diversity were important predictors of nymphal infection prevalence. In conclusion, this study suggests that biodiversity on the West coast may play an important role in reducing Lyme disease in wildlife communities.
