You're not the only one who has wondered what Lyme disease is. Famous people like Yolanda Baldwin and Alec Baldwin are open about their battles with this illness. According to the Centers for Disease Control and Prevention, Lyme disease is a bacterial infection that can be spread through tick bites. The CDC declares that it is the most widespread vector-borne illness in the U.S. It affects about 3000 Americans every year, and causes symptoms such as fatigue, headache, fever or a rash around the tick bite.