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.

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.

Lyme disease is spread by black-legged ticks that are found across the country, including Washington state. Here's how to spot and treat the symptoms.