As if the spread of Lyme disease isn't troubling enough, another illness spread by deer ticks is emerging, experts say.

Powassan virus, which is a far rarer and more deadly pathogen than the bacterium that produces Lyme, is also transmitted by the deer tick. The virus can cause inflammation in the brain, which leads to death or permanent disability in 60 percent of cases.

So far, 75 instances of severe disease have been reported to the Centers for Disease Control and Prevention. Just last week a 5-month-old baby from Connecticut was diagnosed after developing neurological symptoms.

“The bottom line is that we should be very scared of it because nobody is safe from it,” said Dr. Jennifer Lyons, chief of the division of neurological and inflammatory diseases at the Brigham and Women’s Hospital and an assistant professor of neurology at the Harvard Medical School. “And it could be that it is emerging and will explode over the next few years.”

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