Phylodynamics of deer tick virus in North America.

The burden of ticks and the pathogens they carry is increasing worldwide. Powassan virus (POWV; Flaviviridae: Flavivirus), the only known North American tick-borne flavivirus, is of particular concern due to rising cases and the severe morbidity of POWV encephalitis. Here, we use a multifaceted approach to evaluate the emergence of the II POWV lineage, known as deer tick virus (DTV), in parts of North America where human cases occur. We detected DTV-positive ticks from eight of twenty locations in the Northeast USA with an average infection rate of 1.4 per cent. High-depth, whole-genome sequencing of eighty-four POWV and DTV samples allowed us to assess geographic and temporal phylodynamics. We observed both stable infection in the Northeast USA and patterns of geographic dispersal within and between regions. A Bayesian skyline analysis demonstrated DTV population expansion over the last 50 years. This is concordant with the documented expansion of Ixodes scapularis tick populations and suggests an increasing risk of human exposure as the vector spreads. Finally, we isolated sixteen novel viruses in cell culture and demonstrated limited genetic change after passage, a valuable resource for future studies investigating this emerging virus.

Jamestown Canyon Virus in Collected Mosquitoes, Maine, United States, 2017-2019.

Jamestown Canyon virus (JCV) is a mosquito-borne arbovirus that circulates in North America. We detected JCV in 4 pools of mosquitoes collected from midcoastal Maine, USA, during 2017-2019. Phylogenetic analysis of a JCV sequence obtained from Aedes cantator mosquitoes clustered within clade A, which also circulates in Connecticut, USA.

Prevalence and Genetic Characterization of Deer Tick Virus (Powassan Virus, Lineage II) in Ixodes scapularis Ticks Collected in Maine.

Deer tick virus (DTV) is a genetic variant of Powassan virus (POWV) that circulates in North America in an enzootic cycle involving the blacklegged or "deer tick," Ixodes scapularis, and small rodents such as the white-footed mouse. The number of reported human cases with neuroinvasive disease has increased substantially over the past few years, indicating that POWV may be of increasing public health importance. To this end, we sought to estimate POWV infection rates in questing I. scapularis collected from four health districts in Maine (York, Cumberland, Midcoast, and Central Maine). Infection rates were 1.6%, 1.7%, 0.7%, and 0%, respectively, for adults collected from April to November in 2016. Adults collected in October and November in 2017 from York and Cumberland counties had slightly higher rates of 2.3% and 3.5%, respectively. There was no difference in the number of males verses the number of females infected. All positive samples were of the DTV (lineage II) variant. Phylogenetic analysis was performed on 8 of the 15 DTV sequences obtained in 2016. Deer tick virus from the coastal regions were genetically similar and clustered with virus strains isolated from I. scapularis from New York State and Bridgeport, CT. The two inland viruses were genetically nearly identical and grouped with viruses from Massachusetts, Connecticut, and New York. These results are the first reported infection rates and sequences for POWV in questing ticks collected in Maine and will provide a reference point for future POWV studies.