_http://www.ajtmh.org/cgi/content/full/79/6/971_
(http://www.ajtmh.org/cgi/content/full/79/6/971)
Stable Prevalence of Powassan Virus in Ixodes scapularis in a Northern
Wisconsin Focus
Abstract
Deer tick virus (DTV), a variant of Powassan virus (POWV), appears to be
maintained in nature in an enzootic cycle between Ixodes scapularis ticks
and small mammals.
Although POWV infection of human beings is rare, a recent report suggests
increasing incidence and the possibility that POWV may be an emerging
tick-borne zoonosis.
Therefore, we assessed the long-term stability of the POWV transmission
cycle in northwestern Wisconsin.
Adult I. scapularis and Dermacentor variabilis were collected from Hayward
and Spooner, Wisconsin, screened for infection by reverse transcriptase
polymerase chain reaction (RT-PCR), and virus was isolated.
Seventeen of 1,335 (1.3%) of I. scapularis and 0 of 222 (0%) of D.
variabilis ticks were infected. All isolated virus belonged to the DTV genotype of
POWV.
These findings suggest stable transmission of POWV in this focus over ten
years and highlight the potential for this agent to emerge as a public
health concern.
These findings suggest that deer tick-borne POWV may present a public
health risk to human residents of and visitors to infested sites.
Paradoxically, despite the apparent increase in the incidence of human
infection, the proportion of ticks infected remained constant between the
1990s and the present.
The increased geographic distribution of deer ticks and concomitant
increases in their populations might produce a greater number of infected ticks
overall, or might facilitate spillover from cryptic enzootic foci, which
might produce additional human POWV infections.
It may be that a proportion of the recent increase in the recognition of
POWV encephalitis in North America is attributable to the emergence of DTV.
Ongoing studies will therefore more completely characterize the
transmission cycle and molecular epidemiology of DTV within this focus.
Importantly, infection by viruses within the TBE serologic complex results
in a wide range of clinical outcomes, ranging from asymptomatic to severe:
DTV may be less pathogenic than prototypical POWV, as has been suggested
previously.
Experimental studies are required to evaluate this hypothesis. In the
absence of this data, clinicians should consider tick-borne flavivirus
infection in patients presenting 1) with neurologic symptoms and 2) residence or
travel to tick-infested sites.
[Non-text portions of this message have been removed]
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