Tick-borne diseases are on the rise in the United States. Lyme disease is the most commonly reported, with nearly half a million people diagnosed each year. Caused by the bacterium Borrelia burgdorferi, it is most often spread by bites from blacklegged ticks. Lyme can be treated with antibiotics, but if untreated, infection can spread to the joints, heart and nervous system, and some people can experience persistent symptoms.