Genetic Analysis of Powassan virus Genotypes Circulating in North America [University of Findlay]

Abstract

Powassan virus (POWV), a tick-borne flavivirus, is the only member of the tick-borne encephalitis serogroup found in North America. Two distinct lineages, prototype lineage (POWV, lineage I) and deer tick virus (DVT, lineage II) are maintained in enzootic transmission cycles by different tick species based on different geographical regions. In North America, Ixodes scapularis acts as the primary vector throughout the Northeast, and Ixodes cookei throughout the Midwest and much of Canada. Importantly, the incidence of human disease due to POWV has increased by 671% over the last 18 years; with DVT perhapes being the most worrisome genotype due to the wide spread range and prevalence of the vector species. The aim of this study is to assess the evolutionary dynamics of the POWV/DTV complex using the most current full-genome, envelope, and 3’UTR sequences available. Bayesian phylogenetic inferences support the two distinct, monophyletic lineages corresponding to POWV and DTV. Additional analysis were performed in order to quantify the degree to which viral phenotypic characters (such as geographic location, and host species utilization) are correlated with shared ancestry within the two different genotypes. The results of this phylogeny-trait correlation analysis suggest significant clustering of viral sequence by sample location. Such in situ evolution is compatible with the relatively limited distances traveled by most ticks and their prefered host species. Lastly, genetic recombination analysis shows no evidence of between genotype recombination, however further analysis needs to be conducted using within genotype recombination analysis as recombination events may be restricted to only closely genetically related viruses.