Lyme disease incidence is currently on the rise in northern New England, meaning that it is increasingly important to understand the disease and its ecological determinants. The changes in biotic and abiotic factors that occur with increasing elevation are similar to changes due to geographical climatic variation. Therefore, patterns observed along an elevational gradient may provide insights into the influence of climate on disease dynamics. Recent studies have shown that Borrelia burgdorferi infection rates and genotype distribution are influenced by climate and vector seasonality in the United States, and a number of studies in Europe have established a negative correlation between elevation and Borrelia infection. In this study we investigated elevation’s effect on (a) the density and infection of Ixodes scapularis ticks, and (b) the proportion of two common mouse hosts, the cryptic species Peromyscus leucopus and Peromyscus maniculatus, and their infection rate. Small mammal trapping and tick collection were carried out at 13 deciduous forest sites in Addison County, Vermont ranging from 113 m to 569 m in elevation. Mice were identified using a multiplex polymerase chain reaction (PCR) assay. Tick and mouse infection rates were determined using PCR amplification of a conserved region of the Borrelia ospC gene.
Adult and nymphal I. scapularis densities were negatively correlated with elevation. A threshold relationship fit better than a linear one, with a cutoff for nymphal densities at 300m above sea level. A greater proportion of P. maniculatus were infected than P. leucopus. In addition, a significantly higher fraction of trapped mice were P. maniculatus at higher elevations. Ultimately, this study demonstrates that the ecology of Lyme disease changes along an elevational gradient; future research will improve understanding of the environmental determinants of Lyme disease risk in northern New England and inform disease management and prevention efforts.