Tick-borne Powassan virus on the rise

It’s helpful first to read my post from last May about Powassan.  This is a followup report about what we know now that we didn’t know then:

Powassan is on the rise in Maine – Maine CDC

More than half of moose and deer in Maine have been exposed to Powassan – Maine Medical Research Center Institute

It is expected that existing tick-borne encephalitis vaccines would have some benefit against Powassan – Dr. Amesh Adalja

Let’s back up one year…

It’s been almost a year since I wrote about Lyn Snow’s death in December, 2013, from the tick-borne Powassan virus, the last person in Maine to contract the encephalitis-like disease. The post attempted to tell a little of her personal story, of the dangers of this very rare but exceptionally hazardous pathogen, of different things people can do to protect themselves from ticks. But that story was far from complete. My wife and I had become good friends with Lyn and her husband Jack in the previous months (their house is just a few doors up the road from us) and I felt it appropriate to omit a number of details about the progress of her disease and how the medical community responded to it. There’s no need to fill in those blanks now, but those who read “between the lines” in my post got the message: it took doctors and hospitals a very long time to suspect, and then identify – Powassan as the bug that got her. The virus is so rare it wasn’t really on their screen. (That’s now changed, because of the wide publicity surrounding her death.)


No matter, though. From the time the tick bit her on the shoulder, Lyn had virtually no chance. Though she was physically fit and energetic and full of enthusiasm and laughter and everything else that radiates good health, her entire physical makeup – her personal biology – was somehow ideally suited to host this virus, which rapidly multiplied and overwhelmed her in a matter of just a few days. This is not the case with most other Powassan victims. About half of them make a full, or nearly full, recovery. And it is also known that there are many, many people who have gotten the virus from a tick bite and have shown no symptoms whatsoever.

We also know that had Lyn gotten enough of the right “supportive care” earlier on, she would not have wanted to continue living with such severe neurological disability. She’d made this very clear to Jack and other family members, so that aggressive medical intervention in her case would have been essentially moot.


Powassan, an encephalitis-like pathogen, is neuroinvasive. It attacks the central nervous system, including the brain, and when the viral load is heavy enough it causes general (“nonspecific”) swelling. There’s a point at which brain tissue is so damaged it stops functioning.



The MRI photos here are of the head of a 67-year old Powassan female victim from Minnesota who eventually died of the disease. The top image was taken 4 days after her admission to the hospital, and it shows moderate swelling.

The bottom image, showing more severe swelling, was taken just four days after the first one.

From what I’ve read of this case, it closely parallels Lyn Snow’s.

(photos courtesy U. S. Centers for Disease Control and Prevention)

The latest on Powassan: it’s in 2-4% of deer ticks around us, and on the rise

Since it’s spring and deer ticks (I. scapularis) are here again in their nymph stage, I wanted to get the latest and best information on Powassan, especially here in Maine. But let’s start with the big view:

  • First, in Maine, most deer ticks carry disease-causing pathogens. Depending on your source, between 40% and 70% carry Lyme, which is bacterial. Some carry anaplasmosis, also bacterial. Some carry babesiosis, a protozoan. And between 2% and 4% of deer ticks carry Powassan, the only tick-borne virus in the United States, according to surveillance projects in various parts of the northeast (including Connecticut). So, if you do the math, about 80% (or more) of deer ticks are carrying some pathogen that can seriously hurt or kill you.
  • The tick population in Maine has increased hugely over the last 20 years, and continues to grow every year. Deer ticks are now in all of Maine’s 16 counties, but they’re more heavily concentrated in the southern half of the state and Midcoast.
Submission of ticks to Maine Medical Research Center, 1992 and 2012.

Submission of deer ticks to Maine Medical Research Center, 1992 and 2012.

  • I reported this earlier, but here it is again: though the sample is very small – some 60 cases over the last 20 years – Powassan is fatal in about 10% of reported cases. An additional 40% to 50% suffer lifelong severe neurological damage.
  • I also reported that transmission time from tick to human is nearly instantaneous – that once the tick starts feeding in you, you have the virus. This is not quite accurate: studies from Tennessee show transmission time to be a couple of minutes or so. Other studies show a somewhat longer transmission time.
  • There is no vaccine for Powassan, and no cure.


In preparing this post, I connected with several different people, either by phone or email, representing different areas of knowledge about Powassan. I’ve found it nearly impossible to pull them all together into a single coherent package, so I won’t. I’ll do it the easy way, one by one.


Dr. Amesh Adalja, Senior Associate, University of Pittsburgh Medical Center, Center for Health Security

Dr. Adalja knows gobs about Powassan and other vector-borne viruses, including the families of tick-borne encephalitis viruses (TBE) prevalent in much of Europe and Asia, but not at all in North America. A TBE vaccine has been available for some time in Europe, Asia, and Canada, and has shown itself very effective in preventing disease. Wait, why Canada, if TBE doesn’t exist in North America? Well, Canada does things a little differently from the U.S., where the vaccine is not available, because Canadians do travel from time to time to TBE infested areas, and the government thought it wise to offer them vaccinations before they travel. If you live in the U.S. and want to travel to a tick-infested area in Russia, say, then you may have to stop off in Montreal first to get vaccinated.

I was curious to know how similar Powassan and TBE viruses might be. They’re cousins, but how close? He wrote,

Powassan is part of the TBE complex which includes several different viruses that are all related, but not identical in their genetic sequence. Powassan shares about 76% genetic similarity with other members of the complex.

Well, I thought, could the TBE vaccine be helpful against Powassan?

It is expected that existing (TBE) vaccines would have some benefit against Powassan.

But then, you can’t get the vaccine here in the U.S.  Then how about using the existing TBE vaccine as a kind of “starter-kit” to develop a Powassan vaccine?

POW is definitely a relatively rare disease and that disincentives vaccine manufacturers.

Finally, I wanted his thoughts on whether Powassan might be increasing in prevalence. He wrote,

It’s unclear that the number has increased because testing has not been done on an annual basis and as people become more aware of the virus, testing has increased. I would suspect that Powassan has always been present at some level in the tick population


Sara Robinson, Infectious Diseases Epidemiologist, Maine CDC

Maine CDC epidemiologist Sara Robinson focuses on all things vector-borne: pathogens from ticks and mosquitoes. Because prevention has such strong emphasis at Maine CDC, she presents to schools, businesses and at other events to talk about tick and mosquito-borne diseases and how to protect yourself from them.

I had a brief phone conversation with Sara and I can best summarize her statements thus:

Yes, surveillance indicates Powassan is on the rise in Maine. Fortunately, the public and medical community are much more aware of the virus than they were just a few years ago. But there’s more of it around us than a few years ago.

I asked her, only half jocularly, “Why are there ticks?” She says she’s actually asked this question quite a lot. “There seems to be no ecological purpose for ticks.” Likewise, she noted, with cockroaches – there’s just no good reason for them.

But her best news of the day is that Maine’s Health and Environmental Testing Laboratory in Augusta (known as HETL) will be soon be testing for pathogens within Bio Safety Level 3 facilities (bio safety levels run from 1 to 4), including polymerase chain reaction (PCR) testing for anaplasmosis, babesiosis, ehrlichiosis, and Powassan. This means that people suspected of having any of these infections can have blood/serum samples tested right here in Maine, instead of being sent off to the federal CDC facility in Ft. Collins.

This is actually remarkable news – a small state like Maine having such an elaborate and sophisticated human pathogen testing facility. Very cool.


CBL flagging for ticks
Chuck Lubelczyk, Vector Ecologist, Maine Medical Research Center Institute, Scarborough, ME
Recent studies have suggested that the incidence of human POWV (Powassan virus) infection is increasing in the United States, raising the possibility that POWV… constitutes a mounting threat in regions where I. scapularis ticks (deer ticks) are abundant.

– Seroprevalence of Powassan Virus in New England Deer, 1979–2010 (Nofchissey and others, including Chuck Lubelczyk)

Full report here: PowassanNofchissey et al 2013 AMJTMH DTV in Deer

Chuck and his team are the only ones doing active surveillance of Powassan and other vector-borne pathogens among animals in Maine, especially deer and moose, which are ready targets for ticks. They’ve been collecting blood samples from deer and moose brought into registration during hunting season, and are compiling maps and data about the harvested animals. One alarming finding:

More than half of the deer and moose blood samples they tested were positive for Powassan. The animals don’t get sick from it, but it shows the wide prevalence of the virus in deer ticks that they’re host to.

His team also is testing for West Nile virus (which is still extremely rare this far north) and Eastern Equine Encephalitis (EEE), which, like Powassan, is on the rise. The EEE virus is every bit as dangerous and nasty as Powassan, with many of the same symptoms for the disease.

Prevention: Guinea Hens?

Somehow this came up in our phone conversation – using guinea hens to keep the tick population down. Nonsense! says Chuck. He insists the business of guinea hens controlling ticks is pure urban legend, because someone famous talked about it on TV sometime. Sure, guinea fowl might munch on a tick from to time, but not enough to make much difference.


Griffin Dill - University of Maine Cooperative Extension
Griffin Dill, University of Maine Cooperative Extension Tick Identification Lab

Griffin was a helpful participant in my post from last May. He now writes:

The Tick ID Program is entering its second year in operation and is now identifying tick specimens free of charge. Due to the biosecurity of our current lab space, we currently offer tick identification services but cannot test ticks for pathogens. Upon completion of the newly approved diagnostic lab, we will be able to offer disease screening. (Note: this is the University of Maine lab whose funding was approved by voters on a referendum in last fall’s election, but it’s still in the early planning stages. The lab will test for pathogens within ticks and mosquitoes – not humans).

An educational website (http://extension.umaine.edu/ipm/tickid/) has been created to provide information on the biology and management of the state’s 14 different tick species. The site also includes tick submission instructions, tick removal guidelines, a gallery of tick photos, and links to information on tick-borne diseases.

Public participation in the submission of tick specimens and the reporting of tick-borne disease is critical in tracking Maine’s tick population distribution and the prevalence of tick-borne diseases. To facilitate participation in the tick submission process, the University of Maine Tick ID Program is now offering a FREE tick identification service for the people of Maine.

Free! That’s good news. There was quite a lot of animated discussion last year about their former $10 submission fee (per tick). Thank you, Griffin.

(I also connected via email with Marc Fischer, who coordinates the CDC’s ArboNet passive surveillance program – or arthropod-borne viruses – in Ft. Collins, Colorado. He reported no significant changes in Powassan reporting last year from the annual median of 7 cases. He did note, however, an increase around the U.S. in awareness and testing of the virus.)



It comes down to one word: permethrin. See my previous post.


The unanswered question

The more research I dug into, the more intrigued I became with the similarity between the Powassan virus and the complex of tick-borne encephalitis viruses (TBEs) in Europe in Asia, for which there is a very effective vaccine. Dr. Adalja thinks the existing TBE vaccine, which is not available in the U.S., could have good effect against Powassan infection. And it stands to reason that, if this were the case, developing a Powassan vaccine based on the chemistry of the TBE vaccine shouldn’t be too difficult (of course I’m no virologist, so this is wild speculation…)

But the exceptional rarity of Powassan infection is, as he notes, a “disincentive” for drug companies.

Still, and here’s the big question: why must profit be a driver for developing a life-saving drug?

I’ll leave it at that.


I’m dedicating this post to the memory of our late friend Lyn, and to her widowed husband Jack Snow and his large and wonderful family who’ve been here in South Thomaston for hundreds of years. Jack just turned 91, and is as robust and vigorous and fast-witted as anyone I know of any age. My wife and I feel privileged to be their friends.

Ned White

About Ned White

Ned White is a writer, novelist, crossword puzzle constructor, traveler through 49 states, and at times a danger in the kitchen. He lives with his wife in South Thomaston.