As tick season starts, another transmittable illness looms: Powassan virus

Ticks can spread Lyme disease and give people red meat allergies, and now there’s increasing worry in Minnesota about another ailment spread by the blood-sucking pests: the Powassan virus.

While the Powassan virus is uncommon compared to other tick-borne diseases in the state, it is among the most serious, said Elizabeth Schiffman, epidemiologist supervisor at the Minnesota Department of Health (MDH). Carried by blacklegged ticks (more commonly known as deer ticks) the Powassan virus can cause neurological damage and, in rare cases, death.

Last year, there were 14 reported cases in Minnesota — the highest reported since recordkeeping on the disease started in 2008, according to MDH data. In 2011, the state recorded the first death caused by the virus after a woman in her 60s died of a brain infection.

“The risks are relatively low, however, all the tick prevention that you would do to keep yourself from getting one of those more common diseases will also help keep you safe from getting Powassan,” Schiffman said.

It’s likely that many people who are infected with the Powassan virus don’t show the symptoms or only have mild symptoms, she said. Signs include fever, headache, vomiting and weakness.

In severe cases, the virus can cause seizures and swelling of the brain and membranes around it. People who are most likely to suffer severe effects are those who are elderly or immunocompromised.

According to MDH data, Minnesota reported fewer than five cases each year from 2008-2015, except for in 2011 when 11 cases were reported. Between 2016-2023, there were five to eight cases reported each year, except for in 2018 when there were three cases. MDH does not have Powassan virus data for 2020.

The emerging number of Powassan cases in Minnesota is one of the reasons the National Institutes of Health gave Matthew Aliota, associate professor at the University of Minnesota’s Department of Veterinary and Biomedical Sciences, a $3.5 million grant to study the virus in 2024, Aliota said. Aliota is studying the virus in two of the nation’s epicenters over the course of the five-year grant: Minnesota and New York.

About 10% of people who are clinically diagnosed with the virus die, Aliota said. Those who survive a severe bout of the virus may suffer long-term symptoms like headaches and memory problems.

Research indicates it can take minutes from when a tick bites for the virus to pass to humans, he said.

“The Powassan virus is ... an understudied virus,” he said. “It’s one more thing on the list of reasons of why you should be diligent in terms of taking precautions to prevent tick bites.”

Aliota said one of the main issues with trying to find cases of Powassan is that it only shows up in the blood for a short time. Aliota said it’s hard to know for certain how long it shows up in human blood, but in animals it stays in blood for about seven to 10 days. Plus, someone who contracts it may confuse symptoms like aches and pains for a different illness.

“We don’t understand everything there is to know about this virus,” he said. “What we do know is that if you are infected with it, there can be some really severe symptoms because it’s a virus that can invade the central nervous system and go to your brain.”

In Minnesota, the risk of getting bitten by blacklegged ticks starts as the weather warms up in the spring, Schiffman said.

Because an adult blacklegged tick is about the size of a sesame seed and younger ones are even smaller, it can be hard to spot them before they bite, Schiffman said.

Because there is no medicine to treat the virus, the best ways to protect against bites are pre-treating clothing and gear with permethrin-based repellents and using insect repellents on the skin, Schiffman said. It’s best to wear long-sleeved shirts and pants. Wearing light-colored clothing can help with spotting ticks.

Another measure to prevent ticks: tumble dry clothing and gear on high heat for at least 60 minutes after spending time in an area where ticks live.

According to the Centers for Disease Control and Prevention, there were 54 cases of the virus in 2024 nationwide, but it’s likely that a lot more people contracted the virus than what is being reported, Schiffman said.

“One of the reasons there are so few cases and that we don’t know as much about it as we do some of the other infections people get is because testing isn’t widely available for Powassan,” she said. “I think there’s probably a lot of people that could have it, especially in those mild cases, and they’re not ever getting it detected and reported.”