Abstract
BackgroundPowassan virus (POWV; genus Flavivirus) is the sole North American member of the tick-borne encephalitis sero-complex and an increasing public health threat in the USA. Maintained in nature by Ixodes spp. ticks, POWV has also been isolated from species of other hard tick genera, yet it is unclear if these species can serve as vectors. Dermacentor variabilis and Amblyomma americanum share geographic and ecologic overlap with Ixodes spp. ticks and POWV transmission foci, raising the possibility that POWV could become established in these tick species and leading to range expansion and increased human risk. Therefore, we assessed the competency of Ixodes scapularis, D. variabilis and A. americanum for POWV lineage II (POWV II).MethodsLarvae from all three species were co-infested on POWV-infected Balb/c mice. The engorged larvae were allowed to molt to nymphs and screened for the presence of POWV II RNA by reverse transcription-qPCR. Eight infected nymphs from each species were allowed to individually feed on a naïve mouse. Mice were screened for the presence of POWV II RNA to determine infection status.ResultsThe results demonstrated that larvae from all three tick species were able to efficiently acquire POWV II via feeding on viremic mice, maintain infection through molting and successively transmit POWV to naïve mice at the nymphal stage at comparable rates across all three species.ConclusionsOur findings reveal that non-Ixodes tick species can serve as competent vectors for POWV and highlight the potential role of these species in the ecology and epidemiology of POWV. Future studies examining the possible implications of these findings on POWV epidemiology and the adaptability of POWV in these new vectors are warranted.Graphical abstract
Highlights
Powassan virus (POWV; genus Flavivirus) is the sole North American member of the tick-borne encephalitis sero-complex and an increasing public health threat in the USA
POWV consists of two genetic lineages (POWV I and POWV lineage II (POWV II) [deer tick virus]) that are maintained in distinct transmission cycles [7, 8]
Species composition of emerged nymphs and POWV‐II transmission To examine the competency of I. scapularis, D. variabilis and A. americanum to serve as vectors for POWV II, Balb/c mice were intraperitoneally injected with POWV II and co-infested with each of the three tick species
Summary
Powassan virus (POWV; genus Flavivirus) is the sole North American member of the tick-borne encephalitis sero-complex and an increasing public health threat in the USA. There are no vaccines or therapeutics, and very little is known about POWV evolution, epidemiology, transmission and pathogenesis. Answering these basic questions will be critical to countering this threat and eventually reducing POWV disease risk. POWV I is maintained in a transmission cycle between Ixodes marxi and Ixodes cookei ticks and small to medium-size rodents [9, 10]. These tick vectors are generally highly host specific and rarely encountered by humans. The recent identification of a hybrid of I. scapularis and I. cookei suggest that POWV I and II may have experienced analogous evolutionary paths [15]
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