The pandemic of plague, probably both bubonic and pneumonic, first hit Europe between 1347 and 1351, taking more lives than any other known epidemic or war up to that time. This disease was transmitted by the rat flea.
Bubonic plague constitutes about three-fourths of plague cases.
Most characteristic is the early appearance of buboes, which are usually distributed in the groin and armpits. Septicemic plague may prove fatal before there is time for pneumonia to develop. If, however, pneumonia does occur, the patient becomes highly infectious. His contacts will contract pneumonic, not bubonic, plague. Pneumonic plague is nearly always fatal.