To the Editor:
Karl Nelson (Feb. 2, Letter to the Editor, “A new tick-borne threat”) obtained some incomplete information, or misconstrued what he was told.
There are two types of Powassan virus, prototype Powassan and deer tick virus. The UMass lab runs an assay that uses POW1 and POW2 primers in a polymerase chain reaction. The two reagents are needed together to detect either kind of virus. I am sure that UMass did not say that the tick was infected with both kinds of virus.
It is no secret or surprise that deer tick virus (which is almost certainly what the UMass lab found) is in Martha’s Vineyard ticks. There was a severe case of what was then simply called Powassan virus in an M.V. resident in 1994. I have found this virus all over M.V., and pretty much any time I look. It has been there at least since 1994. The mystery is that people don’t seem to frequently get infected … note that the letter writer himself states that he remains without symptoms, and we know he had a virus-infected tick on him. I have concluded that deer tick virus is not terribly infectious, even though there are increasing numbers of cases being reported in the past few years, probably because of better detection by physicians (the virus is a relative of West Nile virus, and some of those tests will pick up evidence of deer tick virus), and also because of the changing American demographic (more elderly and immunocompromised people around).
The life cycle of this virus is pretty much the same as that for the agent of Lyme disease. Deer ticks pick it up from mice and transmit it back to mice. Deer ticks may also inherit the virus. The prototype Powassan virus is indeed maintained in woodchuck ticks, but these ticks may infest skunks and raccoons; they do on M.V. I have looked very hard, over 10 years, for evidence of the prototype Powassan on M.V. in skunks and raccoons, with the help of people like Walter Wlodyka, T.J. Hegarty,and Luanne Johnson, and have never found it — only deer tick virus in deer ticks and mice.
There is no reason to consider deer tick virus as Tickmageddon. We know about this virus. I discovered the deer tick virus in 1997. There is information on the MVTBDI website about it. Yes, it can be transmitted much more rapidly than the other deer tick–transmitted infections, but despite that, with 0.5 percent to 2 percent of all the deer ticks containing virus in many sites, including on Martha’s Vineyard, we have not seen an epidemic of severe neurologic disease. As an epidemiologist, I call that empiric evidence that the theoretical risk for some reason is not becoming a realized risk.
As with all tick-borne infections, personal protection is critical. Wear repellent. Treat your clothes with permethrin. Take a shower, and do a tick check. Be aware of any unexplained fever, and see a healthcare provider. There is, however, no need to get hysterical over a tick bite. The vast majority of bites do not result in infection.
Sam Telford, Sc.D.
Professor of Infectious Disease and Global Health