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

Powassan virus in Maine is a growing concern. Although rare, the virus can be severe, with a fatality rate of approximately 10%.

In 2013, a Maine woman died from the disease, and by 2017, 10 residents had been infected.

An increase in cases of Powassan virus is particularly concerning given that there is no specific treatment and the infection can lead to long-term neurologic complications. Transmission may occur in as little as 15 minutes after a tick bite.

Survey of Tick-Bitten Maine Residents

A study by Smith and colleagues examined the prevalence of Borrelia burgdorferi, Borrelia miyamotoi, and Powassan virus among Maine residents exposed to tick bites.

Using a tick identification database, the authors surveyed 230 individuals bitten by Ixodes scapularis (deer ticks) or Ixodes cookei ticks between 2009 and 2013. Nearly all participants (99%) had been bitten by I. scapularis.

Testing Results

The study found:

• 13.9% positive for B. burgdorferi (Lyme disease)
• 2.6% positive for B. miyamotoi
• 0.9% positive for both infections
• 0.4% positive for Powassan virus

“Among residents of southern Maine with a history of I. scapularis tick bites,” the authors write, “seropositivity for B. burgdorferi was 5 times greater than for B. miyamotoi and 35 times greater than for Powassan virus.”

Although Powassan virus prevalence remains low, frequent exposure to tick bites and rapid transmission raise important clinical concerns.

Borrelia miyamotoi May Be Underdiagnosed

Out of 1,854 reported Borrelia infections in Maine in 2017, only 6 were attributed to B. miyamotoi.

Given a seroprevalence of approximately 2% in this study, the authors suggest that B. miyamotoi is likely underdiagnosed.

This highlights the importance of evaluating patients for a broader range of tick-borne co-infections, not just Lyme disease.

Clinical Perspective

While Powassan virus in Maine remains rare, its severity and rapid transmission make it clinically significant. At the same time, clinicians should remain alert to treatable infections such as Lyme disease and B. miyamotoi, which may be more common but underrecognized.

In one reported case, an adolescent initially diagnosed with Powassan virus was later found post-mortem to have Lyme carditis—a potentially treatable condition.

Dr. Daniel Cameron, MD, MPH
Lyme disease clinician with over 30 years of experience and past president of ILADS.

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