Officials in California shut down recreational sites in South Lake Tahoe this week after a dead chipmunk infected with bubonic plague was found. The plague is a highly infectious bacterial disease spread by rodents bitten by infected fleas, and it ravaged Europe in the 14th century killing tens of millions of people. Humans can contract the disease by flea bites and contact with infected animals, including domestic pets. Unlike the era of the Black Death, new cases of bubonic plague are rare in humans because the infection is easily treatable with antibiotics.