What to know about Powassan virus, a tick-borne disease that can cause fatal brain infection

• Powassan virus is a relatively rare tick-borne disease that can be deadly if it reaches the brain.
• It's transmitted by the deer tick, which also spreads Lyme disease.

The blacklegged or deer tick is best known for spreading Lyme disease, but it can transmit various other viruses through its bites.

Powassan virus is rare compared to other tick-borne diseases that affect humans. Most infections are reported in the Northeast and Great Lakes regions, where the deer tick is active from late spring through mid-fall.

Two other tick species — groundhog ticks and squirrel ticks — can spread Powassan virus if they feed on animals that are infected, according to the Centers for Disease Control and Prevention. The deer tick is much more likely to bite and infect people.

Just 20 human infections with Powassan virus were reported to the CDC in 2020, the most recent year with complete data available. In 2019, the agency counted 39 cases of Powassan virus — a big jump from the previous year.

The reported number of Powassan cases has climbed over the past decade, according to the CDC. Early symptoms tend to be non-specific and may be confused with other endemic diseases, so it's important to know if you have a high risk of infection based on your location and lifestyle.

About 1 in 10 severe Powassan infections is fatal

People who get sick from Powassan virus typically develop symptoms within a month of a tick bite, but many do not have symptoms at all.

It's not clear how many asymptomatic Powassan virus infections occur each year, as they're not usually reported. Humans are known as "dead end hosts" for the virus, according to the CDC, because they cannot spread it to other people or animals.

Those who do have symptoms may experience fevers, headaches, vomiting, and general weakness starting about a week after exposure.

In some cases, the virus can cause infection and swelling around the brain and spinal cord. Symptoms of severe disease include confusion, loss of coordination, difficulty speaking, and seizures.

About one in every 10 cases of severe disease caused by Powassan virus is deadly, according to the CDC. An adult in Maine died in April after being hospitalized with neurologic symptoms caused by the virus.

Approximately half of the people who survive severe Powassan go on to have long-term health problems, such as recurring headaches, trouble with memory, and loss of muscle mass.

The best way to avoid Powassan virus is to look out for ticks

There is no specific treatment for Powassan virus infection, but it's important to seek medical attention if you think you might have it. Severe cases may require hospitalization to support recovery and reduce swelling in the brain.

The best way to avoid the virus, as well as other tick-borne diseases, is to be aware of your risk of tick bites. People who work or play outside in areas where the Powassan virus is active (primarily northeastern states, as well as Wisconsin and Minnesota) have an increased risk of infection, the CDC says.

Powassan virus is mainly spread by immature ticks, called nymphs, that are about the size of a poppy seed. Adult ticks are larger and easier to spot, so people are more likely to remove them before the insect sinks its mouth parts in.

To avoid getting sick, make sure to remove ticks promptly if you find them on your body or on your pets. The CDC also recommends treating clothing and outdoor gear with permethrin, a tick repellent, or using an EPA-approved insect repellent, if you live in a high-risk area.