Former U.S. Sen. Kay Hagan died Monday at age 66 — nearly three years after she was first hospitalized with what doctors later said was encephalitis. The Centers for Disease Control and Prevention describes Powassan virus as an illness spread by the bite of infected ticks. Encephalitis is an inflammation of the brain often caused by an infection like the Powassan virus, according to the Mayo Clinic. "The recovery process for viral encephalitis varies by case with differing impacts on the brain, speech, vision, memory and muscle control.."