Lyme disease is a severe infectious illness caused by the bacterium Borrelia burgdorferi and transmitted by tick vectors (Ixodes scapularis). Both the range of ticks and Lyme disease have been rapidly expanding in Canada, which has led to the establishment of a national medical surveillance program and prompted investigations in Lyme disease as research priority. Furthermore, ticks are responsible for the transmission of other pathogens of relevance to health, including fungi, protozoan and bacterial species. Whereas climate change is a known determinant for the expansion of this disease, little is known about the genetic and molecular mechanisms acting on the vector that underlie the increased risk of disease. We will examine the extent of vector genomic variation in two endemic areas, namely Vermont and Québec Eastern Townships and how this relates to the rate of Borrelia infection. We will define the full spectrum of pathogenic and symbiotic microbial communities (the microbiome) colonizing the vector, and investigate the impact of vector genomic variation on the composition of these communities. In turn, we will address whether the vector microbiome influences the risk of vector infection and pathogen transmission.