Williams is testing whether vaccinating mice against Borrelia burgdorferi, the bacterium that causes Lyme disease in the United States, can reduce the proportion of ticks that are infected. Health officials are looking on with interest. Connecticut has one of the highest rates of human Lyme disease in the country, and June is peak time for transmission. Borrelia burgdorferi infects an estimated 329,000 people in the United States each year, according to the US Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia. And although most people who get prompt treatment recover quickly — Williams has had Lyme three times — up to one in five develops long-term and potentially life-threatening symptoms, including heart, vision or memory problems, or debilitating joint pain.