A tick-borne virus that can cause severe encephalitis is drawing the attention of public health authorities in North America. According to data from the U.S. Centres for Disease Control and Prevention (CDC), the United States reported a record high of 76 cases of Powassan virus infection in 2025. Previously, the country’s annual average number of cases was only 7-8. According to the annual report of the Quebec Institute of Public Health (INSPQ), two cases of encephalitis caused by the Powassan virus were reported in the Mauricie-et-Centre-du-Québec region of Quebec in 2024.
The virus is named after Powassan, a town in the Parry Sound region of Ontario, where the world’s first death related to the virus was recorded as early as 1958.The main vector for Powassan virus is the black-footed tick (deer tick). The risk period is concentrated from late spring to early autumn. Compared to Lyme disease caused by tick bites, the Powassan virus infects much faster: it takes only 15 to 30 minutes after a bite for the virus to cause infection, while Lyme disease usually takes 24 to 48 hours.
As Dr. Parada, a medical consultant at the National Pest Management Association of Chicago, worried: “Powassan virus is more dangerous than Lyme disease because it spreads so quickly—you simply don’t have time to get to the hospital.” [Special Reminder] There is currently no specific treatment or vaccine for Powassan virus. In contrast, early diagnosis and appropriate antibiotic treatment can usually cure Lyme disease. Symptoms of Powassan virus infection are as follows: The incubation period is usually 1 to 4 weeks.
Afterward, some patients may experience symptoms such as fever, headache, vomiting, and fatigue. Note: Most infected individuals are asymptomatic. Severe cases may develop into encephalitis or meningitis, with complications including seizures, confusion, speech or walking difficulties, and even coma. • The mortality rate for severe cases is close to 10%.
Note: Encephalitis is an inflammation of the brain parenchyma, mainly affecting neuronal function; meningitis is an inflammation of the meninges, mainly affecting cerebrospinal fluid circulation. The causes, symptoms, and prognoses of the two are different.
Appendix: Main symptoms of Lyme disease The symptoms of Lyme disease vary depending on the stage of infection and are usually divided into three stages, but the symptoms of each stage may overlap, and some patients may not show typical early symptoms. Early local symptoms (3-30 days after tick bite)
Approximately 70-80% of those infected will develop a characteristic “migratory rash” at the bite site. This rash usually starts as a small red dot and gradually enlarges over several days, sometimes reaching a diameter of over 30 centimetres.
Circular rashes may form a bullseye or bullseye appearance, may feel warm to the touch, but are usually painless and non-itchy. In addition to a rash, early symptoms may include: fever, chills; headache, fatigue; muscle and joint pain; stiff neck; and swollen lymph nodes. It is important to note that approximately 20-30% of Lyme disease patients do not experience symptoms (or do not notice the rash), making early identification more difficult.
Early dissemination symptoms (days to weeks after the bite) If left untreated in the early stages, the infection can spread from the bite site to the whole body. At this point, the following may occur: • Multiple small migratory erythema appeared on other parts of the body. With increased outdoor activities, the risk of tick bites has risen. Just a week ago, Quebec’s public health agency upgraded its warning, adding more towns to its risk list.