About Powassan Virus

Powassan virus is an illness spread by ticks. In Wisconsin, it is spread to humans by the bite of an infected deer tick, also known as the black-legged tick.

Powassan virus is very rare in Wisconsin. The first case identified in Wisconsin was in 2003. Since then, most cases of Powassan virus have been documented in northern Wisconsin. Nationally, Powassan virus cases are most common in the northeast and the Great Lakes region.

Anyone can get Powassan virus, but people who spend more time outdoors are at a higher risk of being bitten by an infected tick. Ticks can be found in areas with woods, brush, or tall grass. Ticks are most active from May to September, but it is important to use caution year-round.

Map of total Powassan virus cases in Wisconsin 2003-2018

 How is Powassan virus spread to humans?

Powassan virus is spread to people through the bite of an infected deer tick. Ticks get the virus by biting an infected mammal, usually small rodents.

Tick rests on a leaf

  • It is not yet known how long an infected tick must be attached to a person to spread Powassan virus, but it is likely less than 12 hours and could be as little as 15 minutes. To prevent getting sick, it is important to remove ticks as soon as they are found.
  • Most people are infected by immature ticks, called nymphs.
    • Nymphs are very small, about the size of a poppy seed. They are difficult to see, and most people may not feel their bite. This makes them harder to remove promptly.
    • Nymphs are most active during the spring and early summer.
  • Adult ticks also spread Powassan virus.
    • Adults are much larger than nymphs, and are more likely to be found and removed before the virus is spread to the person.
    • Adult ticks are most active during the cooler months.
  • Ticks can attach to any part of the body but are often found in hard-to-see areas, such as:
    • Behind the knees
    • Armpits
    • Scalp
    • In and around the ears
    • Inside the belly button
    • Groin

Powassan virus is preventable. Visit our Tick Bite Prevention page to learn how to prevent tick bites, and how to properly remove a tick if you are bitten.

 What are the signs and symptoms of Powassan virus?

Symptoms can show up one week to one month after being bitten by an infected tick.

Many people who become infected with Powassan virus do not have any symptoms. In those who do have symptoms they may develop between one to five weeks after a tick bite.

Common early signs and symptoms include:

  • Fever
  • Headache
  • Nausea
  • Vomiting
  • Muscle weakness
  • Stiff neck

Severe illness can include:

  • Confusion
  • Loss of coordination
  • Paralysis
  • Speech difficulties
  • Seizures
  • Memory loss
  • Encephalitis (inflammation of the brain)
  • Meningitis (inflammation of the membranes around the brain and spinal cord)

It is important that you see your doctor right away if you have any of these symptoms after being outdoors, even if you do not remember being bitten by a tick. Powassan virus can be a very serious illness. Approximately 10% of severe Powassan virus cases are fatal. Approximately half of survivors of severe disease have permanent or long-term neurologic symptoms, such as recurrent headaches, memory problems, and muscle wasting.

 How is Powassan virus treated?

There is currently no treatment or vaccine for Powassan virus. Over-the-counter pain relievers may be given to relieve symptoms. In severe cases, patients may need to be hospitalized to receive supportive treatment. If you believe you or a family member may have Powassan virus, contact your doctor immediately.


DHS resources
Centers for Disease Control and Prevention (CDC) resources
Partner resources
Powassan virus is preventable. Visit our Tick Bite Prevention page to learn how to protect yourself from Powassan virus and other illnesses spread by ticks.

Questions about illnesses spread by ticks? Contact us!
Phone: 608-267-9003 | Fax: 608-261-4976

Last Revised: June 29, 2020