Powassan virus

noun

Po·​was·​san virus pə-ˈwä-sən- 

variants or less commonly Powassan

1

: a flavivirus (Orthoflavivirus powassanense) that is transmitted to humans by infected ixodid ticks (especially deer ticks) and that causes a sometimes life-threatening illness

The first case, in 2008, involved a child with encephalitis who was found to be infected with the Powassan virus, an arbovirus that is related to West Nile virus.

—Bridget M. Kuehn

2

or Powassan disease or Powassan virus disease : the illness caused by the Powassan virus that is typically marked by fever, headache, weakness, confusion, loss of coordination, seizures, and often encephalitis or meningitis but that may sometimes be asymptomatic

Note: Powassan virus was first reported in the Canadian municipality of Powassan, Ontario in 1958. The illness typically occurs in the northeastern U.S. and Great Lakes region.

Don't just worry about Lyme disease this summer—Powassan virus is also spread by ticks, and doctors say it could be much more dangerous.

—Charlotte Alter

Severe Powassan often needs hospitalization to receive respiratory support, intravenous fluids or medications to reduce swelling in the brain.

—Nina Radcliff

… blacklegged ticks can also transmit anaplasmosis, babesiosis and Powassan disease according to the Centers for Disease Control and Prevention.

—Andy Ouriel

—abbreviation POW, POWV see also Powassan encephalitis

Examples of Powassan virus in a Sentence

Recent Examples on the Web

The rare but increasingly prevalent Powassan virus, spread mainly by the black-legged tick, can reach the brain and cause encephalitis. —Kate Wong, Scientific American, 22 June 2026

John Reagan, 66, an avid outdoorsman from New Hampshire, remains hospitalized in Boston after contracting Powassan virus, according to his longtime friend and Tom Wright. —Aaron Parseghian, CBS News, 17 June 2026

Powassan virus is named after Powassan, Ontario, in Canada, where it was first discovered in 1958, according to the Minnesota Department of Health. —Emily Vetter, USA Today, 16 June 2026

Bites can cause Lyme disease, anaplasmosis, babesiosis, Powassan virus. —Sophie Lindberg, Kansas City Star, 8 June 2026

Word History

Etymology

after Powassan, town in Ontario, where an infection with the virus occurred in 1958

First Known Use

1959, in the meaning defined at sense 1

Rhymes for Powassan virus

• adenovirus
• baculovirus
• coronavirus
• enterovirus
• poliovirus
• antivirus
• herpesvirus
• parvovirus
• reovirus
• retrovirus
• rhinovirus
• rotavirus

Medical Definition

Powassan virus

noun

Po·​was·​san virus pə-ˈwä-sən- 

variants also Powassan

1

: a flavivirus (Orthoflavivirus powassanense) that is transmitted to humans by infected ixodid ticks (especially deer ticks) and that causes a sometimes life-threatening illness

2

or Powassan disease or Powassan virus disease : the illness caused by the Powassan virus that is typically marked by fever, headache, weakness, confusion, loss of coordination, seizures, and often encephalitis or meningitis but that may sometimes be asymptomatic

Note: Powassan virus was first reported in the Canadian municipality of Powassan, Ontario in 1958. The illness typically occurs in the northeastern U.S. and Great Lakes region.

—abbreviation POW, POWV see powassan encephalitis