Powassan Virus Disease
When was Powassan discovered?
POW virus was first discovered in 1958 in patients suffering from encephalitis in the town of Powassan, Ontario, Canada. POW virus was detected 12 years later in the United States, where the first case was diagnosed in New Jersey in 1970.
How common are cases of Powassan virus? 
Cases of POW virus are rare; however, the number of cases have increased in recent years. According to the Centers for Disease Control and Prevention (CDC), there were approximately 397 reported cases of POW virus between 2004 and 2024. POW virus is most common in the Northeastern and Great Lakes regions of the United States, with disease transmission hot-spots reported in Wisconsin, Minnesota, Massachusetts and New York.
How can I get Powassan virus?
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Ixodes scapularis life stages
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POW virus is only transmitted by the bite of an infected tick. The most common POW virus vector is the blacklegged tick (“deer tick"),
Ixodes scapularis, which readily feeds on humans. Groundhog ticks
(Ixodes cookei) and squirrel ticks (Ixodes marxi) can also transmit POW virus, but neither prefers to feed on humans. Studies show that all three ticks can transmit the disease in as little as 15 minutes of feeding, so preventing tick bites is extremely important. The ticks that carry POW virus are active whenever temperatures are above 37oF; therefore, medical providers should consider POW virus disease in patients with encephalitis symptoms outside of mosquito season.
How serious is Powassan virus disease?
Like other insect- and tick-borne diseases, infection with POW virus may not cause any symptoms (asymptomatic infection), or may cause a mild, flu-like illness. However, if the virus infects the brain, it can cause a condition called encephalitis. Encephalitis caused by POW virus is often associated with significant, long-term illness, and is fatal in about 10 percent of reported cases. Approximately half of patients who survive the encephalitis form of the disease suffer permanent brain damage.
What are the symptoms of infection with Powassan virus?
Symptoms of Powassan encephilitis appear suddenly and can develop from 7 to 30 days after a bite from an infected tick. When POW virus attacks the central nervous system, it kills cells and causes the brain to swell. The membranous coverings of the brain and spinal cord (called “meninges") can also swell, causing meningitis. This swelling causes a variety of symptoms ranging from mild to severe. Symptoms may include headache, fever, vomiting, confusion, speech difficulty, memory loss, tremors, seizures, difficulty breathing, muscle weakness, and paralysis. The incubation period is 7-30 days.
How is Powassan virus disease diagnosed?
A medical provider can diagnose POW virus disease based on symptoms and with blood and spinal fluid test results. Both blood and spinal fluid tests detect the antibodies the body makes as it fights the POW virus infection. There are no specific treatments or medications for Powassan virus disease. Medical care is purely supportive, addressing disease symptoms, and could include nursing support, breathing assistance (a ventilator), and intravenous fluids.
What can I do to reduce my risk of becoming infected with Powassan virus disease?
AVOID TICK BITES! The DoD Insect Repellent System is the best method of tick bite protection. It incorporates permethrin repellent on the uniform; DEET, picaridin, or IR3535 repellent on exposed skin; a properly worn uniform; and sleeping inside a permethrin-treated bed net. When in tick habitat (tall grass and weeds, scrubby areas, woods, and leaf litter), routinely check your skin, clothing, and gear for ticks. Do a careful check of your whole body once you go indoors. The CDC recommends taking a shower soon after being outdoors. Ticks can be very small; look for new "freckles" or moving specks of dirt. Remove ticks as soon as they are found.
Select the image for more information on the DoD Insect Repellent System.
