HABITAT ASSOCIATIONS OF A POWASSAN VIRUS FOCUS IN SOUTHERN MAINE

Abstract

Deer Tick virus (DTV) is a recently discovered lineage of Powassan virus and a member of the greater tick-borne encephalitis complex of viruses (TBEC) and causes significant morbidity and mortality to infected humans. DTV is associated with Ixodes scapularis ticks which are endemic to much of the Eastern and Midwestern United States and regularly bite humans. DTV, like other members of the TBEC, is thought to exist in small focal locations where transmission patterns are maintained over time. A field site was established on the Southern coast of Maine where high rates of DTV were found in questing ticks during 2018 and 2019. Host and tick abundance along with vegetation and microclimate conditions were measured in second growth forests across a gradient of infestation by invasive understory shrub species. DTV infection rate, was higher in the forest site highly invaded by Japanese barberry compared to forest sites moderately invaded or with native understory vegetation only. A higher density of I. scapularis was associated with Japanese barberry invasion, as well as a higher white-footed mouse abundance and lower saturation deficit. These findings are consistent with the theory of nidality (focality) of vector-borne infection in which zoonotic agents are maintained through an ideal assemblage of pathogen, hosts and habitat.