the bubonic plague

Bubonic plague is an acute infection in humans and various species of rodents, caused by Yersinia pestis (formerly called Pasteurella pestis), a bacterium transmitted by fleas that have fed on the blood of infected rodents, usually rats. The ingested plague bacteria multiply in the flea's upper digestive tract and eventually obstruct it. When the flea feeds again on a human or another rodent, the obstruction causes the freshly ingested blood to be regurgitated back into …

…the years and conferred a relative immunity to many people. That plague does recur indicates its existence as a chronic disease among wild rodents. Prevention The most effective way to prevent plague is to reduce the rodent and flea populations by the use of proper sanitation and rodenticides and insecticides. The plague organism is vulnerable to the antibiotics streptomycin, chloramphenicol, and tetracycline, if treatment is started within about 15 hours of the first appearance of symptoms.