Plague, playg, is both the name of a serious infectious disease caused by the bacterium Yersinia pestis and a term used to describe epidemics generally. This article discusses the disease caused by Y. pestis. The bacterium is named after French scientist Alexandre Yersin, who first identified it in Hong Kong in 1894. Since early times, epidemics of plague have killed hundreds of millions of people. Plague bacteria infect rodents, such as rats, ground squirrels, and prairie dogs. The bites of fleas transmit the germs from rodent to rodent and from rodents to human beings or pets.