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Another Tick-Borne Disease Growing in the United States: Powassan Virus

Contagion® sat down with Holly Frost, MD, pediatrics physician scientist at the Marshfield Clinic Research Foundation, in Minocqua, Wisconsin, to discuss the emerging infectious disease, Powassan virus. 

What is Powassan virus? 

Powassan virus is a tick-borne flavivirus that was first discovered in Ontario in 1956. Powassan virus is known to be carried by the Ixodes scapularis, or the black-leg tick, which is also known as the deer tick. That’s the same vector that carries Lyme disease, Anaplasma, and Babesia.  
It’s a relatively newly discovered virus, and so we don’t know exactly how prevalent it is in humans in the United States, but we do know that about 7% of ticks in endemic areas for Lyme disease also carry Powassan virus, and that in some mammal populations in the Northeast, up to 90% of the population can have Powassan virus. 

What is the Prevalence of Powassan virus in Humans in the United States? 

This was the first study that looked at the prevalence of Powassan virus in humans. We found that, of patients presenting in the Upper-Midwest with suspected tick-borne disease, about 10% of patients had serologic evidence of Powassan virus.
We also looked at patients who were presenting just for routine chemistry screening, and we found that about 4% of those patients had serologic evidence of a past Powassan virus infection. We know that the prevalence in humans is likely to be higher than what we had previously estimated, because the [virus’s] prevalence in ticks is growing; so, about 7% of Ixodes scapularis ticks in some endemic regions now carry Powassan virus, and up to 90% of mammals in some endemic regions of New England have serologic evidence of Powassan virus. 

Why Should Healthcare Providers Be Aware of Powassan virus? 

Powassan virus can cause severe neurologic symptoms, including encephalitis in some patients. The majority of the patients likely present with an asymptomatic infection, or just a mild febrile illness. We don’t really know which patients are likely to develop encephalitis or neuro-invasive diseases, and so, if you live in an area that’s endemic for Lyme disease, it’s important to consider [Powassan virus] if you have a patient who is critically ill. 

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