Project Summary Lyme disease, one of the most commonly reported infectious diseases in North America, is caused by the tick-borne bacterium Borreliella burgdorferi. Although humans and other large mammals can be infected by B. burgdorferi, in order to complete its life-cycle in the wild the bacteria relies on rodent reservoirs, the major one being Peromyscus leucopus, the white-footed deermouse. The role of P. leucopus in Lyme disease and several other tick-borne diseases is analogous to that of bats as reservoirs for SARS coronaviruses and Ebola virus. In this proposal we continue the development of P. leucopus as an emerging genetic model system for the study of infectious and other diseases by maintaining and expanding genomic and biological resources for this species. These resources are the starting point for any gene-focused experiments in the Peromyscus genus. The primary goal of this proposal is to identify segregating genetic factors that impact the competence of P. leucopus as a reservoir of B. burgdorferi. The trait of reservoir competence is measured as the prevalence of infection and corresponding bacterial burdens among a cohort of nymphs that had molted from larvae previously fed on experimentally-infected deermice. Secondary endpoints include rates of growth and decline of the bacteria in the blood and skin of the animals and selected host responses, such as antibodies to the agent and inflammation of tissues, over the time course of the infection. It would normally be extremely difficult to carry-out large-scale genotyping and/or genetic crosses in an emerging rodent model. Here we show that our genome assembly for P. leucopus in concert with low pass short read sequences from a long-term closed colony of deermice can be leveraged to accurately impute SNP and haplotype genotypes on a genome- wide scale. These genotypes are then used to identify genes contributing to the remarkable capacity of P. leucopus to serve as a key reservoir host for B. burgdorferi and other disease agents. Finally, a subset of identified genes will be validated via CRISPR/Cas9 gene knock-outs in P. leucopus spearheaded by the person who pioneered transgenics for this genus. The identification of reservoir competence mediating genes may suggest better interventions to block transmission and provide insights into the management of human infections.