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You're likely aware of the risks of contracting Lyme disease and do what you can to lower the odds you’ll get it. But now experts say there’s another tick-borne illness you should be aware of—and it can be much worse than Lyme.

Before you worry too much, know that this illness, Powassan virus, is rare. An average of seven cases have been reported a year in the U.S. from 2006 to 2015—and reported cases have been limited to a few states, including Wisconsin, Minnesota, New York, and Massachusetts, according to the Centers for Disease Control and Prevention. For comparison, in 2015 there were 28,453 cases of confirmed Lyme disease across the United States, along with 9,616 probable cases, per the CDC. But cases might rise in the near future, and experts are concerned.

Up until now, it's been rare for ticks that usually bite humans to carry Powassan virus.

Powassan is related to the West Nile virus, according to the CDC. Historically, it’s carried by several different ticks: Ixodes cookei and Ixodes marxi, which rarely bite humans. But now the disease has shown up in Ixodes scapularis (i.e., deer ticks), which frequently bite humans and are also responsible for spreading Lyme disease.

As a result, “more people may potentially become exposed,” Richard Watkins, M.D., M.S., an associate professor of internal medicine at Northeastern Ohio Medical University and an infectious diseases physician in Akron, Ohio, tells SELF. This is bad news because Powassan can result a more severe illness than Lyme: 10 percent of Powassan virus cases are fatal, according to the CDC, while deaths related to Lyme disease are so uncommon that the CDC doesn't actually track them. "Death from Lyme disease is rare as all stages are treatable by antibiotics," Amesh A. Adalja, M.D., a board-certified infectious disease physician and affiliated scholar at the Johns Hopkins Center for Health Security, tells SELF.

And, here’s where it gets really unnerving: Transmission of the virus can occur within 15 minutes after the tick attaches to a person, as opposed to the minimum 36 to 48 hours a tick needs to be attached to transmit Lyme.

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Symptoms of Powassan virus can present in many ways—or not at all.

“Some people will only have a fever while others develop neurological symptoms such as confusion and seizures,” Watkins says. “Long-term neurological complications are common.”

Other symptoms include chills, muscle aches and pains, headaches, and paralysis, Adalja says, noting that the disease can also cause encephalitis, which is an inflammation of the brain that can be deadly or lead to permanent disability, or meningitis, an inflammation of the membranes that surround the brain and spinal cord. However, he adds, like Zika virus, some people can contract Powassan virus and have no symptoms at all.

There's no specific treatment for the disease. “Patients who develop seizures can be treated with anti-seizure medications, and physical and occupational therapy can help those with neurological complications,” Watkins says. People with severe cases are typically hospitalized, observed, and given supportive care to help control their symptoms, Adalja says.

Given the serious nature of the disease, experts say it’s best to try to do what you can to avoid being bitten by a tick in the first place.

The CDC points out that it’s important to be wary of ticks all year, but people should be especially vigilant from April to September when these bugs are most active.

To protect yourself, the CDC recommends wearing repellent that contains 20 percent or more DEET, picaridin, or IR3535 on exposed skin and avoiding wooded and brushy areas with high grass and leaf litter. If you go hiking, walk in the center of trails instead of near the brushy edges, where ticks may be lurking. When you come indoors, try to shower within two hours and do a full-body tick check with a mirror to help you inspect hard-to-see places. It’s also a good idea to regularly inspect your pets since ticks can latch onto them, come indoors, and attach to a person later.

If you suspect that you may have contracted Powassan virus, alert your doctor immediately. You’ll likely be given a blood test or cerebrospinal fluid testing to confirm a diagnosis, Adalja says.

While the virus’ move to the deer tick population is concerning, you shouldn’t panic over it. “It is still a rare infection, although people should be careful to avoid tick exposure and remove them as soon as they are discovered,” Watkins says.

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This story originally appeared on Self.

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