The tick-borne disease—which singer Justin Timberlake revealed this week he has been suffering from—is increasing in the U.S. both in range and frequency.

According to the CDC, early signs and symptoms of Lyme disease appear 3 to 30 days after a tick bite, and include fever, chills, headache, fatigue, muscle and joint aches. One of the hallmark symptoms of Lyme disease is a bullseye-like rash, though it can appear in other shapes as well.

As pop star Justin Timberlake shares his diagnosis of Lyme disease, his ordeal brings up questions. What is Lyme disease and its cause? How is the illness treated? A doctor explains.