It started with vomiting and a fever. But a few days later, five-month old Liam was in the emergency room, his tiny body gripped by hourly waves of seizures. X-rays and MRIs showed deep swelling in his brain. When an infectious disease specialist at Connecticut Children's Medical Center diagnosed Liam with Powassan virus in November, he became the first recorded case in state history. Doctors think Liam picked up the rare neurological disease from a tick his father brought back after a deer hunting trip.

The toddler survived with some scar tissue—but not everyone who gets Powassan, POW for short, is so lucky. With no treatment available, half of all people who contract the virus suffer permanent brain damage; 10 percent die. And while POW is nowhere near as prevalent as that other tick-borne summer scourge—Lyme—it is starting to show up more often.