Health: Infectious Disease Epidemiology & Prevention Division: Powassan Virus

Powassan Virus

Powassan virus is an arthropod-borne virus (arbovirus) that can cause severe illness in people. While most arboviruses that cause human illness are transmitted by mosquitoes, Powassan virus is transmitted by infected ticks. In the Upper Midwest, Powassan virus is transmitted by the blacklegged tick (Ixodes scapularis). Local transmission of Powassan virus has not been detected in Indiana.

Transmission

Powassan virus is transmitted to people primarily by the bite of an infected tick. In the Upper Midwest the blacklegged tick (Ixodes scapularis) is the infecting tick species. Ticks become infected when they feed on groundhogs, squirrels, mice, or other rodents that have the virus in their blood. People do not develop high enough levels of the virus in their blood to infect biting ticks. As a result, people are considered "dead-end" hosts for Powassan virus. The virus is not transmitted from person-to-person, except rarely by blood transfusion. Because the virus can be transmitted through blood, persons who were recently diagnosed with Powassan virus infection should not donate blood or bone marrow for 120 days following infection.
Signs and Symptoms
Many people infected with Powassan virus do not develop any symptoms. For those who do, signs and symptoms usually appear within 1–4 weeks of the bite of an infected tick. Signs and symptoms of Powassan virus disease can include:
- Fever
- Headache
- Vomiting
- Weakness
- Confusion
- Loss of coordination
- Speech difficulties
- Seizures
The most severe cases of Powassan virus disease can include encephalitis (inflammation of the brain) and meningitis (inflammation of the membranes that surround the brain and spinal cord). Among people with severe disease, about half will have permanent complications, such as recurrent headaches, muscle wasting and memory problems. Approximately 10% of severe Powassan virus disease cases are fatal.
Diagnosis

Diagnosis of Powassan virus disease is based upon the patient’s signs and symptoms, a history of possible exposure to ticks, and appropriate laboratory testing. If you think that you have Powassan virus disease, contact your health care provider right away.
People who have removed an attached tick sometimes wonder if they should have it tested for tick-borne diseases. Although some laboratories offer this testing, ISDH does not recommend it. If the tick tests positive, it does not necessarily mean that you have been infected; if the tick tests negative, it may provide a false sense of security because you may have been unknowingly bitten by a different tick that was infected.
Treatment
Prevention
Maps and Statistics
Resources
Information for Providers
For Powassan virus disease diagnosis, treatment, and testing information, click here.
- Physician Reference: Common tick-borne diseases
- Tickborne Diseases of the United States

Page last reviewed/updated: January 2025