Lyme disease cases in Minnesota are on the rise. The state Department of Health says the number of people contracting the illness jumped 88 percent over the last year. Lyme disease is spread by the deer tick. If left untreated, it can cause arthritis, neurological problems, and heart damage. Dr. Kirk Smith is the state public health veterinarian at the Minnesota Department of Health. He says a number of factors may be contributing to the increase: