Powassan virus is a rare but serious virus transmitted to humans primarily through the bite of infected ticks, especially the black-legged tick, also known as the deer tick. It is a tickborne flavivirus found mainly in North America and the Russian Far East. Powassan virus can cause severe neurological disease, including encephalitis (inflammation of the brain) and meningitis (inflammation of the membranes around the brain and spinal cord). Key points about Powassan virus:

• It can be transmitted to humans within as little as 15 minutes after a tick bite.
• Symptoms may include fever, headache, vomiting, muscle weakness, confusion, lack of coordination, speech problems, memory issues, seizures, and in severe cases, encephalitis or meningitis.
• The disease is rare, with only a few cases reported annually in the U.S., mostly in the Northeast and Upper Midwest.
• About 10% of individuals with severe Powassan virus disease may die.
• Survivors of severe infection may experience long-term neurological complications such as muscle wasting, chronic headaches, and memory problems.
• There is no vaccine or specific treatment for Powassan virus; prevention focuses on avoiding tick bites.

The virus circulates in ticks that feed on small mammals like groundhogs, squirrels, and mice. Humans are considered incidental hosts and usually do not transmit the virus to others, except in very rare cases such as through blood transfusion. Preventative measures include avoiding tick-infested areas, using tick repellents, performing tick checks after outdoor activities, and promptly removing attached ticks. Powassan virus was first identified in 1958 in Powassan, Ontario, after a young boy died from encephalitis caused by the virus. Since then, cases have been reported in the U.S., Canada, and Russia, with an increasing number of cases observed in recent years.