What You Need To Know About Powassan Virus

If talk of this year’s potential tick apocalypse wasn’t bad enough, alarming news of a new tick-borne disease called Powassan virus has taken the internet and local TV stations by storm. While it certainly raises cause for concern, it’s important to get some perspective on this rare disease: know the basics about what it is, how and where you can contract it, and how to protect you and your family.

What is Powassan virus?

Powassan virus (POWV) is a tick-borne encephalitic virus (flaviviridae) and is similar to tick-borne encephalitis virus (TBEV), a neurologic infection spread by ticks in Europe and Asia and other encephalitic viruses spread by mosquitos (e.g. West Nile virus). It is the only tick-borne encephalitic virus in North America.

The first confirmed human case occurred in 1958 when a young boy from Powassan, Ontario died of severe encephalitis and researchers isolated and identified the virus on autopsy. Since then, the majority of POWV cases have been reported from the upper Midwestern and northeastern states.

What are its symptoms?

Fortunately, most people who are exposed to the virus never develop disease. Signs and symptoms of POWV include fever, headache, vomiting, and confusion and disorientation from meningitis and encephalitis (brain swelling). The incubation period ranges from one week to one month from the time of the tick bite.

Roughly 10-15% of people who have developed symptoms have died, and 50% of those surviving a symptomatic illness have long term neurological problems like frequent headaches and memory difficulties. Since it is a virus, antibiotics cannot be used to treat Powassan. Treatment for severe symptoms involves supportive care at a hospital. Currently, there is no vaccine to prevent POWV.

Which ticks carry it?

Female blacklegged tick (Left). Female groundhog tick (Right)

The virus is maintained in nature through three cycles of mammal host and tick vector: the groundhog tick (Ixodes cookei) and groundhogs and skunks, the squirrel tick (Ixodes marxi) and squirrels and chipmunks, and the most implicated in human disease, the blacklegged (deer) tick (Ixodes scapularis) and white-footed mice.

Field studies have demonstrated that American dog ticks (Dermacentor variabilis) are not carrying POWV, mainly because they are not part of these transmission cycles. More study is needed to know the role the Rocky Mountain wood tick (Dermacentor andersoni) plays in POWV maintenance cycles, however it is currently not suspected to transmit the virus to humans.

Powassan virus infection in humans is caused by two closely related, but distinct virus types: Lineage I (Powassan virus or POWV) and Lineage II (deer tick virus or DTV). Humans disease is more often caused by the Lineage II strain because the blacklegged ticks carry it are more likely to bite humans than groundhog or squirrel ticks that carry Lineage I. Both lineages have been shown to cause human disease, and no real differences in disease presentation have been noted between the two types.


What makes this virus more concerning than other tickborne diseases is that it can be transmitted quickly. Unlike most tick-borne bacteria that take hours to days of feeding to transmit an infectious dose, animal models have suggested that it could take as little as 15 minutes to transmit the virus from the bite of an infected tick.

POWV can also be transmitted from an infected female tick to her eggs (i.e. transovarial transmission). However, the chances of infection increase as the tick progressed through each life stage. A bite from a more visible adult blacklegged tick is more risky than a bite from a tiny larval blacklegged tick.

How common is it?

While it’s getting a lot of attention, POWV is still very rare. Only 75 cases have been reported in the U.S. in the last decade (compared to more than 300,000 cases of Lyme disease reported each year), and most cases occurred in the upper Midwestern states around the Great Lakes or in the northeastern states. On average, less than 10 cases are reported each year, and less than 5% of blacklegged (deer) ticks are carrying the virus. Compare this with Lyme disease, where roughly 20% of nymphs and 50% of adult females are infected with the bacteria.

How do I protect myself?

Because the virus can be transmitted so quickly, tick bite prevention is absolutely crucial. Wearing permethrin-treated clothing and footwear and avoiding tick habitat should be your first priorities. Consider wearing skin repellent like DEET (15-33%) as well (reapplying every 4 hours). Conduct regular tick checks both while outdoors and afterwards to ensure you’ve removed any tick found biting. Be sure to use a safe tick removal strategy, take a photo of and save any ticks you find for potential testing.

For more information, go to TickEncounter.org


CDC. 2017. Powassan virus. https://www.cdc.gov/powassan/index.html

Frost HM, Schotthoefer AM, Thomm AM, Dupuis AP II, Kehl SC, Kramer LD. Serologic evidence of Powassan virus infection in patients with suspected Lyme disease. Emerging Infectious Diseases. 2017 Aug. https://doi.org/10.3201/eid2308.161971

Hermance & Thangamani. 2017. Powassan Virus: An Emerging Arbovirus of Public Health Concern in North America. Vector-borne and Zoonotic Diseases. In press.

Knox K, Thomm AM, Harrington YA, Ketter E. 2017. Powassan/Deer Tick Virus and Borrelia Burgdorferi Infection in Wisconsin Tick Populations. Vector-borne and Zoonotic Diseases. In press.

University of Rhode Island TickEncounter Resource Center

Article written by Heather Kopsco, PhD student, Plant Sciences and Entomology Dept. at URI.


Created with images by mislav-m - "What makes you tick" • Myriams-Fotos - "tick common wood bock ixodes ricinus bloodsucking" • Nicooografie - "tick insect harmful animal arachnid"

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