Phylogeographic reconstruction of the emergence and spread of Powassan virus in the northeastern United States

Abstract

Powassan virus is an emerging tick-borne virus of concern for public health, but very little is known about its transmission patterns and ecology. Here, we expanded the genomic dataset by sequencing 279 Powassan viruses isolated from Ixodes scapularis ticks from the northeastern United States. Our phylogenetic and phylogeographic reconstructions revealed that Powassan virus lineage II was likely introduced or emerged from a relict population in the Northeast between 1940-1975. Sequences strongly clustered by sampling location, suggesting a highly focal geographical distribution. Our analyses further indicated that Powassan virus lineage II emerged in the northeastern U.S. mostly following a south to north pattern, with a weighted lineage dispersal velocity of ~3 km/year. Since the emergence in the Northeast, we found an overall increase in the effective population size of Powassan virus lineage II, but with growth stagnating during recent years. The cascading effect of population expansion of white-tailed deer and I. scapularis populations likely facilitated the emergence of Powassan virus in the northeastern U.S.

Comparative pathogenesis of two lineages of Powassan virus reveals distinct clinical outcome, neuropathology, and inflammation

“…For example, disease severity, fatality rate, and long-term sequelae associated with TBEV infection has been shown to vary depending on the subtype despite the high sequence similarity between these viruses (23,24). Similarly, DTV and POWV share approximately 94% amino acid identity and 84% nucleotide sequence similarity and are serologically indistinguishable (6)(7)(8).…”

“…Lineage II Powassan virus is also known as Deer tick virus (DTV) and was initially isolated in 1995 and is vectored primarily by Ixodes scapularis ticks (3,4). Powassan virus and DTV share approximately 84% nucleotide sequence identity and 94% amino acid identity but are serologically indistinguishable (5)(6)(7)(8). The number of cases and geographic range for both POWV and DTV have increased, coinciding with the expansion of Ixodes tick and increased surveillance.…”

Emerging tickborne viruses vectored by Amblyomma americanum (Ixodida: Ixodidae): Heartland and Bourbon viruses

“…High homology of HRTV and BRBV RdRps with influenza A and B, THOV, and DHOV PB1 and PA suggest similar endonuclease and RNA synthesis activity that contribute to this diversification (Staunton et al 1989, Leahy et al 1997, Weber et al 1998, Walter et al 2011). While the tick-borne Powassan virus (POWV, Flaviviridae ) and Tick-borne encephalitis virus (TBEV, Flaviviridae ) demonstrate relative evolutionary stasis, long-term diversification with consequences for virus ecology and transmission has occurred (Bondaryuk et al 2023, Vogels et al 2023). In addition, the unique capacity for reassortment of the segmented HRTV and BRBV genomes can be a source of rapid genetic change with the potential to significantly influence transmission and disease, as demonstrated with DBV and THOV reassortment in vertebrate and tick vectors (Davies et al 1987, Jones et al 1987, Lam et al 2013, Liu et al 2016).…”

“…populations. It is hypothesized that transovarial transmission and cofeeding on vertebrate hosts may be primarily responsible for POWV maintenance, and similarly could play a role in HRTV and BRBV circulation (Vogels et al 2023). The vector competence studies discussed above support both cofeeding and transovarial transmission as possible mechanisms for HRTV and BRBV in A. americanum (Godsey et al 2016, 2021).…”