Lyme disease isn’t the only tick-borne illness that can come from a walk in the woods. Health experts are warning that another pathogen, Powassan virus, can cause dangerous inflammation in the brain and may be transmitted to humans much faster than Lyme. While it is rare, a recent study of ticks in Maine, along with a few widely reported cases of human infection, suggest that it may be becoming more common.

What is Powassan virus?

The virus causes encephalitis, or swelling of the brain, and it kills about 10% of people who become sick, according to the Centers for Disease Control and Prevention (CDC). About half of people are left with permanent neurological problems.

Powassan virus was first identified in 1958 and was first recognized in deer ticks, the type that bite humans and also carry Lyme disease, in the mid-1990s. About 75 cases have been reported to the CDC over the last 10 years, and most have been in the Northeast and the Great Lakes region.

One of those cases, in 2013, was a woman in Maine who died a few weeks after being bitten by a tick and contracting Powassan virus. Her diagnosis, along with two subsequent cases in the same county, prompted scientists at the Maine Medical Center Research Institute to test ticks at various sites across the state.

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The researchers released their preliminary findings in April and told the Bangor Daily News that “we were kind of surprised that we found as much as we did.” Out of 203 different pools of adult ticks—meaning all of the ticks collected from a given area—15 tested positive for Powassan. The researchers also found that populations of deer ticks were increasing in several areas in the state.

Another recent CDC case report detailed the first-ever diagnosis of a human Powassan infection in Connecticut: a 5-month-old baby who was admitted to the hospital in November 2016 for vomiting, fever and seizures. The baby’s parents reported that he had been bitten by a tick about two weeks earlier and estimated that the tick bad been attached for less than three hours. The baby spent a week in the hospital, and it took several months for him to fully recover.

Should you be worried about Powassan virus?

This news, coupled with experts’ prediction that 2017 will be an especially bad year for ticks in the Northeast, is cause for concern. So is the fact that Powassan is deadlier than Lyme disease—and appears to be transmitted much faster. In animal studies, Powassan virus could be passed from tick to host after only about 15 minutes of attachment. For Lyme disease, it takes 24 hours.

But Rafal Tokarz, associate research scientist at the Columbia University Mailman School of Public Health, stresses that Powassan is still very rare, and says it’s too early to know for sure if Powassan is truly becoming more prevalent.

Tokarz’s own research, mostly on ticks in regions around New York City, has shown that only about 1% to 2% of ticks are infected with bacteria that cause the Powassan virus. That finding is consistent with most studies that have been done in other parts of the country, he says.

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The recent report from Maine suggests higher numbers, but Tokarz points out that the researches tested entire pools at once. So while about 7% of tick pools tested positive for the virus, “there is no way to know how many ticks in each pool were infected,” he says. “It could be one out of 100, or it could be all 100.”

Nicholas Bennett, medical director of infectious diseases & immunology at Connecticut Children’s Medical Center, says that an increase in reported Powassan cases may also be due to more doctors being aware of the virus and actually testing for it. Like all tick-borne diseases, he says, the CDC’s numbers are probably much lower than the actual number of infections that occur each year, because many go unsolved or misdiagnosed.

In November, Bennett was instrumental in getting that 5-month-old baby tested and diagnosed at Connecticut Children’s. “I may have been the first doctor to pick up on a case of Powassan in this state, but I’m sure it wasn’t the first to see a case in this state,” he says. “This isn’t a virus that’s on our standard list of tests, or that we look for automatically.”

And while some Powassan infections become very serious, many other people only develop a mild illness or have no symptoms at all.

More research is needed to determine how worrying Powassan is. But, Bennett says, research does suggest that tick populations and tick-borne diseases in general are on the rise.

What to do if a tick bites you

If you are bitten by a tick, rushing to the doctor right away won’t do you much good, Bennett says. The tests for these viruses aren’t pleasant—they involve blood and spinal-fluid drawings—and may not show signs of infection for several days or weeks.

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“It’s perfectly reasonable to wait and see if you develop symptoms,” he says. There’s not much doctors can do for people who aren’t seriously ill, anyway. Doctors do not have a cure for Powassan and can only monitor the symptoms and provide care like respiratory support and IV fluids.

“The good news is that if you or your child are feeling a little under the weather or have a low-grade fever, there’s a million other probably causes other than Powassan,” says Bennett. “But if there are neurological symptoms—weakness, dizziness, seizures—then it’s important to get to the doctor.”

How to avoid ticks

The CDC says that people should protect themselves from Powassan virus the same way they do other tick-borne illnesses: by wearing insect repellant when spending time in areas where ticks are present, inspecting clothing and skin afterward and bathing or showering upon returning home. If pets have been outdoors, make sure they’re inspected regularly as well.

“Take precautions and be on the lookout for ticks whenever possible,” Tokarz says. “Whether it’s Powassan or something more common like Lyme or another tick-borne disease, you really don’t want to get any of them.”

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