Lyme disease is the most common disease spread by ticks in the Northern Hemisphere. It is estimated to affect 300,000 people a year in the United States and 65,000 people a year in Europe.he classic sign of early local infection with Lyme disease is a circular, outwardly expanding rash called erythema chronicum migrans (EM), which occurs at the site of the tick bite three to 32 days after the tick bite. The rash is red, and may be warm, but is generally painless.