The virulence of the plague bacillus—that is, its ability to multiply in the tissues of its host and cause death—is remarkably stable and vigorous. Once ingested by a flea, it multiplies until the insect’s digestive tract is blocked. When the flea bites another rodent or a human, bacilli are regurgitated into the new host and migrate through the lymphatic system to lymph nodes. There they are able produce proteins that disrupt the normal inflammatory response and that prevent their digestion by infection-fighting macrophages. With the host’s immune response thus weakened, the bacilli quickly colonize the lymph nodes, producing a painful swelling and, eventually, destroying the tissue. On occasion they enter the bloodstream either directly or from the lymph nodes, bringing on a general septicemia, or blood poisoning. On postmortem examination they are found in great …show more content…
Bubonic plague is the best-known form in popular lore, and indeed it constitutes about three-fourths of plague cases. It is also the least dangerous form of plague, accounting today for virtually no deaths and in the past killing only half of its victims (at a time when contracting the other forms of plague brought almost certain death). Typically, bubonic plague starts two to six days after Yersinia infection with shivering, then vomiting, headache, giddiness, and intolerance to light; pain in the back and limbs; and sleeplessness, apathy, or delirium. The most characteristic sign, however, is the subsequent appearance of one or more tender, swollen lymph nodes, or buboes, which are usually distributed in the groin and armpits. The temperature rises rapidly to 40 °C (104 °F) or higher and frequently falls slightly on the second or third day, with marked fatigue. Bubonic plague is not directly infectious from person to person; the bacillus is carried from rodent to person or from person to person by infected