Powassan Virus in Maine: Prevalence and Tick-Borne Infection Risk

Powassan virus in Maine remains rare but is an important concern because severe neurologic disease can be fatal or result in long-term complications.

In 2013, a Maine woman died from the disease. From 2000 through 2017, 10 Maine residents were reported to have been infected.

Cases have continued to be reported since this study was published. Maine recorded seven cases in 2023, the highest annual number reported by the state at that time.

Powassan virus is particularly concerning because there is no specific antiviral treatment, and severe infection can lead to long-term neurologic complications. Experimental studies indicate that Powassan virus can be transmitted to animal hosts within 15 minutes of tick attachment. The minimum transmission time in humans has not been established.

Survey of Tick-Bitten Maine Residents

A study by Smith and colleagues examined evidence of exposure to Borrelia burgdorferi, Borrelia miyamotoi, and Powassan virus among Maine residents with a history of tick bites.

Using a tick identification database, the researchers surveyed 230 individuals bitten by Ixodes scapularis or Ixodes cookei ticks between 2009 and 2013. Nearly all participants had been bitten by I. scapularis, also known as the blacklegged or deer tick.

Because the participants were selected based on a history of tick bites, the results do not represent the prevalence of these infections in Maine’s general population. The antibody findings indicate past exposure rather than necessarily proving active illness.

Testing Results

The study found:

13.9% were seropositive for B. burgdorferi
2.6% were seropositive for B. miyamotoi
0.9% were seropositive for both Borrelia infections
One participant, or 0.4%, had an equivocal flavivirus-positive result that was not definitively confirmed as Powassan virus exposure

Among these tick-exposed Maine residents, evidence of exposure to B. burgdorferi was substantially more common than evidence of exposure to B. miyamotoi or Powassan virus.

Although evidence of Powassan virus exposure was uncommon in this study, frequent tick exposure and the possibility of rapid transmission raise important clinical concerns.

Borrelia miyamotoi May Be Underdiagnosed

Of 1,854 reported Borrelia infections in Maine in 2017, 1,848 were attributed to Lyme disease and only six were attributed to B. miyamotoi.

Given a seroprevalence of approximately 2% among the tick-exposed participants, the authors suggested that B. miyamotoi disease was likely underdiagnosed in Maine.

This finding highlights the importance of considering a broader range of tick-borne co-infections, rather than focusing exclusively on Lyme disease.

Clinical Perspective

Powassan virus in Maine remains uncommon, but its potential severity makes it clinically significant. Many infected people do not develop symptoms. Among patients who develop severe neuroinvasive disease, approximately 10% die, while some survivors experience persistent neurologic problems.

There is no specific antiviral treatment for Powassan virus infection. Treatment is supportive and may include hospitalization for patients with encephalitis, meningitis, seizures, respiratory problems, or other serious complications.

At the same time, clinicians should remain alert to treatable tick-borne infections such as Lyme disease and B. miyamotoi, which may be more common but underrecognized.

Frequently Asked Questions

How common is Powassan virus in Maine?

Powassan virus disease remains rare in Maine. In this study of 230 tick-exposed residents, one participant had an equivocal flavivirus-positive result, but Powassan virus exposure was not definitively confirmed. These findings should not be interpreted as the prevalence of Powassan virus in Maine’s general population.

What other tick-borne diseases are found in Maine?

Ticks in Maine can transmit Lyme disease, Borrelia miyamotoi disease, babesiosis, anaplasmosis, and Powassan virus disease. More than one infection may sometimes be transmitted by the same tick.

Is Borrelia miyamotoi underdiagnosed?

Possibly. The study found evidence of B. miyamotoi exposure more often than Maine’s reported case numbers would have suggested at the time.

How quickly can Powassan virus be transmitted?

Experimental studies have demonstrated transmission to animal hosts within 15 minutes of tick attachment. The minimum time required for transmission to a human has not been established.

Why is Powassan virus dangerous?

Powassan virus can cause encephalitis, meningitis, seizures, and other neurologic complications. Approximately 10% of people with severe neuroinvasive disease die, and some survivors develop long-term neurologic problems. No specific antiviral treatment is available, so medical care is supportive.