Prevalence and Genetic Diversity of Deer Tick Virus (Powassan Virus, Lineage II) in Ixodes scapularis Ticks in Five Habitats at a Nature Reserve in Southern Maine, United States

Deer tick virus (DTV), also known as Powassan virus lineage II, is a rising health concern due to increased recognition as a cause of human encephalitis. Since European tick-borne encephalitis virus persists in nature in enzootic foci (i.e., higher prevalence rates in small pockets in nature), we sought to determine whether DTV is also focally maintained in relation to habitat type, to better understand factors leading to human risk of exposure. From 2018 to 2021, questing Ixodes scapularis ticks were collected from five habitats at the Wells National Estuarine Research Reserve (WNERR) in Wells, ME: forest with invasive vegetation in the understory, edge, shrub, forest with native vegetation in the understory, and open field. Deer tick virus prevalence was greater in adult ticks (2.0%) than in nymphs (0.5%). Deer tick virus prevalence in adult ticks collected from forest with invasive vegetation was 3.2% compared to 0 to 1.7% in other habitat types. A hot spot analysis revealed a higher number of infected adults collected per hour on one of the transects located in forest with invasive vegetation. Phylogenetic analysis of 37 full-length DTV genomes sequenced in this study revealed four major clades from the WNERR, and there was high genetic diversity within each transect, suggesting frequent, short-range dispersal between habitats. Analysis of DTV sequences from other New England counties and states also indicated long-distance dispersal to and/or from the WNERR. This study provides preliminary evidence that DTV is focal and that the risk of encountering DTV-infected ticks in forest with invasive vegetation may be greater than in other habitat types.