About Powassan Virus
Powassan virus is an illness spread by ticks. It spreads to humans by the bite of an infected deer tick, also known as a black-legged tick.
Powassan virus is rare in Wisconsin. Nationally, Powassan virus cases are most common in the northeast and Great Lakes regions.
The first case in the state was identified in 2003. Since then, most cases of Powassan virus have been in northern Wisconsin.
Anyone can get Powassan virus. People who spend more time outdoors are at a higher risk of getting bitten by an infected tick.
Ticks are commonly found in areas with woods, brush, or tall grass and are most active in Wisconsin during May through November, but they can be active anytime temperatures are above 40°F.
Powassan 101
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.
To prevent getting sick, it’s important to remove ticks as soon as you find them. It isn’t known exactly how long an infected tick must be attached to a person to spread Powassan virus. It’s likely less than 12 hours, and could be as little as 15 minutes.
Most people are infected by immature ticks, called nymphs. Nymphs are very small, about the size of a poppy seed. They’re hard to see. Most people don’t feel their bites. This makes them harder to remove right away. Nymphs are most active during the spring and early summer.
Adult ticks also spread Powassan virus. Adults are much larger than nymphs. They’re more likely to be found and removed before the virus spreads to the person. Adult ticks are most active during the cooler months in early spring and fall.
The image to the right shows an adult deer tick.
Ticks can attach to any part of the body. They often are found in hard-to-see areas, such as:
- Behind the knees.
- In the armpits.
- On the scalp.
- In and around the ears.
- Inside the belly button.
- On the groin.
Powassan virus is preventable and treatable. Learn about Tick Bite Prevention and how to properly remove a tick if you’re bitten.
Symptoms can show up one week to one month after being bitten by an infected tick. Many people who become infected with Powassan virus don’t have any symptoms.
Common early signs and symptoms include:
- Fever
- Headache
- Nausea
- Vomiting
- Muscle weakness
- Stiff neck
Severe illness can include:
- Confusion
- Loss of coordination
- Paralysis
- Speech difficulty
- Seizures
- Memory loss
- Encephalitis (inflammation of the brain)
- Meningitis (inflammation of the membranes around the brain and spinal cord)
See your doctor right away if you have any of these symptoms after being outdoors, even if you don’t remember being bitten by a tick.
Powassan virus can cause serious illness. Powassan virus causes death in about 10% of severe cases. Half of those who survive severe disease have permanent or long-term neurologic symptoms. These can include recurring headaches, memory problems, and muscle weakness or loss.
Currently, there isn’t a treatment or vaccine for Powassan virus. Over-the-counter pain relievers may help with symptoms. In severe cases, patients may need supportive treatment in a hospital. If you believe you or a family member may have Powassan virus, contact a doctor right away.
Resources from the Wisconsin Department of Health Services (DHS)
- Signs and symptoms, treatment, and prevention—Powassan Virus Fact Sheet, P-00355 (PDF)
- Education on the risk posed by illnesses spread by ticks—Tickborne Diseases Risk in Wisconsin, P-01751 (PDF)
- Educational tri-fold card about ticks in Wisconsin, proper removal, and tick bite prevention—Tick Safety Guide, P-01434
- Fact sheet with simple steps to take—Protecting Your Family From Mosquitoes and Ticks, P-02080
Resources from the CDC (Centers for Disease Control and Prevention)
- Signs and symptoms, prevention, and more—CDC Powassan Virus
- Preventing Ticks on Your Pets
- Fact sheet on tick bite prevention for hunters—It’s Open Season on Ticks (PDF)
- Plastic trail sign to remind hikers there are ticks in the area—Prevent Tick Bites (PDF). Order the sign from CDC Publications on Demand.
- Fact sheet on steps to take after a tick bite—Tick Bite: What to Do (PDF).
- Educational comic for kids—Don’t Let a Tick Make You Sick (PDF)
- Educational crossword for kids—Don’t Let a Tick Make You Sick (PDF)
Partner resources
- Information from the University of Wisconsin-Madison Medical Entomology Laboratory—Wisconsin Ticks and Tick-borne Diseases
- Information on ticks found in the Midwest, surveillance resources, and tick biology and development from the Midwest Center of Excellence for Vector-Borne Diseases—Ticks
Contact us
Questions about illnesses spread by ticks? We’re here to help.
Bureau of Communicable Diseases
Phone: 608-267-9003
Fax: 608-261-4976