“Plague” refers to the various forms of disease caused by the bacteria Yersinia pestis. It is carried by Oriental rat fleas which have become established in rodent populations in the Southwest United States, mostly ground hogs. About 20-25 people a year contract Plague – about 1 in 7 die, especially if treatment is not timely. The last major urban outbreak of Plague in the US was in San Francisco between 1900 and 1909; over 120 people died, before a major public health campaign eliminated the disease, but spread it into the native rodents.
For more information, see the Centers for Disease Control (CDC).