The dark legacy of the Black Death

The bacterium Yersinia pestis caused the Black Death plague. It lived in rodents, and fleas that bit infected animals then bit people and passed it on. Most scientists accept this explanation. Medieval doctors knew nothing of bacteria, so their treatments aimed at rebalancing bodily fluids and had no effect.

It spread along trade routes, mainly on ships. Infected rats and their fleas traveled with cargo from Asia to Mediterranean ports, then moved inland. Crowded medieval towns helped, and the pneumonic form of the disease passed between people through coughing, so it crossed most of Europe within a few years.

The name comes from the dark marks the disease left on victims. Black spots appeared on the skin, and in advanced cases, fingers, toes, and the nose turned black as tissue died. Swollen lymph nodes called buboes also darkened. Sources differ on which sign gave the name, so it likely reflects all of them.

Yes, plague still occurs, with a few thousand cases reported worldwide each year, including occasional cases in the United States. It is caused by the same type of bacterium, but antibiotics cure it when given early, so it is far less deadly than it was in the 1300s.