Myositis and flaccid paralysis caused by Powassan virus infection acquired in Manitoba, Canada

Background: Powassan virus is a cause of viral encephalitis transmitted by Ixodes ticks. A few weeks following a tick bite, patients with Powassan virus infection present with fever, encephalitis, disorientation, or aseptic meningitis. 10% of cases are fatal, and 50% of survivors experience long-term neurological sequelae. The diagnosis of Powassan virus is primarily based on serology; however, significant cross-reactivity exists with other flaviviruses. Testing is primarily by serology. Powassan virus polymerase chain reaction can be performed on cerebrospinal fluid, but the virus is rarely detectable by the time patients present with symptoms. Methods: This was a retrospective chart review of a single case of a woman with Powassan virus infection presenting with ascending paralysis. Results: We describe a 73-year-old woman who developed ascending paralysis following a tick bite in southern Manitoba in June 2025. A Powassan virus plaque reduction neutralization test was performed on patient sera that was positive, with a titre of 1:640. Conclusion: While Powassan virus cases have historically been rare in Canada, there has been a significant increase in recent years, particularly in Ontario and Quebec. The first case of Powassan virus in Manitoba was only reported in 2022, and this is the third case now known to be acquired in Manitoba. Powassan virus was made a nationally notifiable disease in 2024. Clinicians should be aware of the increasing incidence of Powassan virus infection in Canada, including its appearance in the Canadian prairies, as well as unusual presentations of infection, including ascending paralysis, and rhombencephalitis.