Powassan virus infection is caused by the RNA virus Powassan virus (POWV), a species under the genus Flavivirus. In Ontario, transmission occurs through the bite of infected blacklegged ticks called Ixodes scapularis (or deer ticks), or less commonly Ixodes cookei (or groundhog tick) or Ixodes marxi (or squirrel tick).
The overall risk of acquiring Powassan virus infection in Toronto is low but is increased if participating in activities in wooded and brushy areas.
For general information about tick-borne diseases including epidemiology and prevention, visit TPH’s Tick-Borne Diseases of Public Health Significance (TBDoPHS) webpage.
Most infections are asymptomatic.
Symptoms usually occur one week to one month after a tick bite. Infected individuals may show mild to severe symptoms.
Symptoms include:
There may be a transient period of remission after the acute febrile phase, followed by worsening neurological deterioration. Severe disease may result in meningitis and/or encephalitis with symptoms that may include confusion, loss of coordination, difficulty speaking, paralysis, seizures or coma.
Approximately, 50 per cent of people who survive severe disease have long-term health problems, such as recurring headaches, loss of muscle mass and strength and memory problems.
Refer to Public Health Ontario’s summary table for distinguishing clinical symptoms between tick-borne diseases of public health significance.
Powassan virus is spread to humans by the bite of an infected tick. It can take as little as 15 minutes for the virus to be acquired from a blood-feeding tick.
Testing is indicated for individuals with compatible clinical symptoms and a relevant exposure history (e.g., outdoor activity in an endemic area, tick bite(s), if known).
Serology is the primary testing for Powassan virus infection.
Serum specimens (acute and convalescent) need to be collected two to three weeks apart. Cross reactivity may occur with other flaviviruses for hemagglutination inhibition (HI) and ELISA methods. Specimens that are HI reactive are referred to the National Microbiology Laboratory (NML) for confirmatory testing by plaque reduction neutralization test (PRNT).
Public Health Ontario Laboratory has information on Powassan virus serology and PCR.
There is no specific treatment for Powassan virus infection. Medical care is supportive to help relieve symptoms.