The negative relationship between mammal host diversity and Lyme disease incidence strengthens through time

Abstract

Since its discovery in 1975, Lyme disease has spread and increased in much of central and eastern United States. Host diversity is thought to play a role in Lyme disease risk, and it has been suggested that the direction of the relationship between host diversity and disease risk may vary depending on the spatial scale of observation. Here we modelled the effect of mammal host species richness on the incidence of Lyme disease from 1992 to 2011 across all states in the United States with reported or established black-legged tick (Ixodes scapularis) populations. We tested two contrasting hypotheses: A positive vs. a negative relationship between host species richness and Lyme disease incidence. We also tested the hypothesis that the strength of the diversity-disease-risk relationship increased over time, as Lyme disease spread. We observed a strong negative relationship between mammal host species richness and Lyme disease incidence, and this relationship became more negative over time. Lyme disease increased over time more rapidly in host species-poor states than host species-rich states. Our findings support the importance of mammal host richness on Lyme disease risk at large spatial scales, and the importance of spatial and temporal scales on the diversity-disease relationship.