Infection with the bacterium Yersinia pestis, transmitted to man by rat-flea bite. Plague still occurs in India, Pakistan, China, Indonesia and Africa, but is now rare in Western Europe. Many rodents are infected with plague bacteria, but only the rat can transmit it to man. The rat flea can only jump short distances, so infection can only be caused by rats living close to man (house or ship rats). There are two forms of plague in man: bubonic and pneumonic. Bubonic plague is characterized by swollen lymph nodes (buboes), usually in the groin.