Powassan Virus Disease: What you need to know

After learning of a recent human case of Powassan (POW) Virus disease in a Connecticut infant (Link 1, Link 2, Link 3), MESH has decided to update its stakeholders on this disease in preparation for a predicted heavy tick season.

POW Virus is an arboviral (any virus that is transmitted by mosquitoes, ticks, or other arthropods) flavivirus (single-stranded, enveloped RNA viruses) first discovered in 1958 in Powassan, Ontario. Two types of POW have been identified in North America; Lineage 1 and Lineage 2 (deer tick virus) POW viruses. The disease is very rare, but it has been predicted to increase in incidence due to the uncharacteristically warm winter in the United States.

The virus is transmitted by the bite of ticks infected with POW virus. In order to transfer the virus to humans, the tick must be attached for a certain amount of time that is still unknown. 6 species of tick have been identified as vectors for the virus: Ixodes cookei, Ixodes scapularis, Ixodes marxi, Ixodes spnipalpus, Dermacentor andersoni, and Dermacentor variabilis.

Humans do not develop high enough concentrations of POW virus in their bloodstreams to infect feeding ticks. Humans are therefore considered to be “dead-end” hosts of the virus. POW virus is maintained in a cycle between ticks and small-to-medium-sized rodents. In North America, three main enzootic cycles occur: Ix. cookei and woodchucks, Ix. marxi and squirrels, and Ix. scapularis and white-footed mice. Ix. cookei and Ix. marxi rarely bite humans. Ix. scapularis often bite humans and is the primary vector of Lyme disease.


For the purpose of surveillance and reporting, based on their clinical presentation, arboviral disease cases are often categorized into two primary groups: neuroinvasive disease and non-neuroinvasive disease.

Neuroinvasive disease: Many arboviruses cause neuroinvasive disease such as aseptic meningitis, encephalitis or acute flaccid paralysis (AFP). These illnesses are usually characterized by the acute onset of fever with headache, myalgia, stiff neck, altered mental status, seizures, limb weakness or cerebrospinal fluid (CSF) pleocytosis. AFP may result from anterior (“polio”) myelitis, peripheral neuritis or post-infectious peripheral demyelinating neuropathy (i.e., Guillain-Barré syndrome). Less common neurological manifestations, such as cranial nerve palsies, also occur.

Non-neuroinvasive disease: Most arboviruses are capable of causing an acute systemic febrile illness (e.g., West Nile fever) that may include headache, myalgia, arthralgia, rash or gastrointestinal symptoms. Some viruses can also cause more characteristic clinical manifestations, such as severe polyarthralgia or arthritis due to chikungunya virus or other alphaviruses (e.g., Mayaro, Ross River, O’nyong-nyong)

Many infected persons may have no symptoms or only mild symptoms. Symptoms of POW virus usually appear within 1-4 weeks of a tick bite. Signs and symptoms may include: Fever, Headache, Vomiting, Weakness, Seizures, Speech difficulties, Encephalitis (swelling of the brain), and Meningitis (swelling of the membranes that surround the brain and spinal cord.) Approximately half of survivors have permanent neurological symptoms, such as recurrent headaches, muscle wasting and memory problems. Approximately 10% of POW virus encephalitis cases are fatal.

Currently, there are no vaccines or medicines to treat or prevent POW infection; therefore, reducing exposure to ticks is the most effective way to avoid POW virus infection. Persons with severe POW illnesses often need to be hospitalized. Treatment may include respiratory support, intravenous fluids, and medications to reduce swelling in the brain.

Currently, there are no vaccines or medicines to treat or prevent POW infection; therefore, reducing exposure to ticks is the most effective way to avoid POW virus infection. Persons with severe POW illnesses often need to be hospitalized. Treatment may include respiratory support, intravenous fluids, and medications to reduce swelling in the brain.

The distribution of one of the primary human-infecting vectors for POW virus, Ix. scapularis, includes large portions of the Southern U.S., Eastern states, the Midwest, and the Great Lakes region. Much of Northern Indiana as well as parts of Central and Southern Indiana are also common areas where Ix. scapularis live. Climate change is expected to expand the natural distribution of arboviral vector species and increase the incidence of arboviral diseases. Additionally, an increase in deer populations and a warmer winter have been indicated as potential routes for increases in the incidence of human POW viral disease.

Reducing exposure to ticks is the best defense against POW virus disease and other tickborne infections. While it is a good idea to take preventive measures against ticks year-round, be extra vigilant in warmer months (April-September) when ticks are most active.

Avoid Direct Contact with Ticks

  • Avoid wooded and brushy areas with high grass and leaf litter.
  • Walk in the center of trails.

Repel Ticks on Skin and Clothing

  • Use repellent that contains 20 percent or more DEET, picaridin, or IR3535 on exposed skin for protection that lasts several hours.
  • Use products that contain permethrin on clothing. Treat clothing and gear, such as boots, pants, socks and tents with products containing 0.5% permethrin. It remains protective through several washings. Pre-treated clothing is available and may be protective longer.
  • The Environmental Protection Agency (EPA) has an online tool to help you select the repellent that is best for you and your family.

Find and Remove Ticks from Your Body

  • Bathe or shower as soon as possible after coming indoors (preferably within two hours) to wash off and more easily find ticks that are crawling on you.
  • Conduct a full-body tick check using a hand-held or full-length mirror to view all parts of your body upon return from tick-infested areas. Parents should check their children for ticks under the arms, in and around the ears, inside the belly button, behind the knees, between the legs, around the waist, and especially in their hair.
  • Examine gear and pets. Ticks can ride into the home on clothing and pets, then attach to a person later, so carefully examine pets, coats, and day packs.
  • Tumble dry clothes in a dryer on high heat for 10 minutes to kill ticks on dry clothing after you come indoors.
    • If the clothes are damp, additional time may be needed.
    • If the clothes require washing first, hot water is recommended. Cold and medium temperature water will not kill ticks effectively. If the clothes cannot be washed in hot water, tumble dry on low heat for 90 minutes or high heat for 60 minutes. The clothes should be warm and completely dry.

Dogs are very susceptible to tick bites and tickborne diseases. Vaccines are not available for all the tickborne diseases that dogs can get, and they don’t keep the dogs from bringing ticks into your home. For these reasons, it’s important to use a tick preventive product on your dog.


Tick bites on dogs may be hard to detect. Signs of tickborne disease may not appear for 7-21 days or longer after a tick bite, so watch your dog closely for changes in behavior or appetite if you suspect that your pet has been bitten by a tick.


To reduce the chances that a tick will transmit disease to you or your pets:

  • Check your pets for ticks daily, especially after they spend time outdoors.
  • If you find a tick on your dog, remove it right away.
  • Ask your veterinarian to conduct a tick check at each exam.
  • Talk to your veterinarian about tickborne diseases in your area.
  • Reduce tick habitat in your yard.
  • Talk with your veterinarian about using tick preventives on your pet.



Centers for Disease Control and Prevention: Link 1, Link 2, Link 3, Link 4

Minnesota Department of Health: Link

United States Geography Services: Link

Greer, A., Ng, V., & Fisman, D. (2008). Climate change and infectious diseases in North America: the road ahead. Canadian Medical Association Journal178(6), 715-722 Link