Borrelia burgdorferi (image) University of Pennsylvania Caption Borrelia burgdorferi is the bacterial culprit behind Lyme disease. A new study by University of Pennsylvania researchers shows that humans can develop immunity to particular strains of the bacteria that protect against reinfection for several years. Credit Courtesy of CDC Usage Restrictions None Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.