She attended Florida State University, where she majored in ballet and American studies and graduated in 1975. She served as an intern in the Capitol Hill office of her uncle, Lawton Chiles, a United States senator from Florida and later the governor there. Her job was operating the senators-only elevator.

She met Mr. Hagan at Wake Forest University School of Law. They married in 1977 and she graduated in 1978. They lived in Greensboro, where he worked in his father’s law firm and she worked for North Carolina National Bank — now Bank of America — in the trust department.

The virus that proved fatal to Ms. Hagan, Powassan (pronounced po-WAH-sun), is named after a town in Ontario, where it killed a boy in 1958. Only six cases were reported in the United States in 2015, according to the federal Centers for Disease Control and Prevention.

But with the tick population exploding, and tick-borne diseases increasing, especially in the Northeast and the Great Lakes region, the number of Powassan cases rose to 21 in 2016 and 33 in 2017. Still, this is a tiny proportion of diseases borne by ticks. The CDC said that about 10 percent of people with a severe case of the virus die and 50 percent experience long-term health consequences.

Mr. Hagan said his family surmised that Ms. Hagan picked up a tick when they were hiking in the Blue Ridge Mountains in Virginia over Thanksgiving in 2016. They had walked through the woods at Peaks of Otter and had a picnic on the grass, where she was probably bitten, he said.

By early December, one side of her face was drooping, and he thought she had had a stroke, Mr. Hagan said. She received a diagnosis of encephalitis, but because the Powassan virus is seen so rarely, it took doctors more than two months to identify it.

The disease, for which there is no known treatment or vaccine, affected her ability to control her muscles, arms and legs and hampered her speech. She had been using a wheelchair since before the diagnosis.