While it is commonly believed that a bacterium carried by fleas caused the Black Death, also known as the Black Plague, more recent epidemiological research suggests that the cause was an airborne contagion spread by sneezes, coughs and touch. Originating in the Far East, the plague in Europe first hit Turkey and several Mediterranean islands, then moved into the northern Mediterranean ports and swept north.
The first round of the Black Plague in Europe began in 1346 and lasted until about 1353. At its height, from 1348 through 1350, the disease killed an estimated 1.5 million Europeans, out of a total European population of about 4 million. In some areas, particularly where people were crowded together or where malnutrition and poor hygiene made them susceptible to disease, the death toll was much higher. In London, the disease had killed about 60 percent of the entire population by the spring of 1349.
Although precisely why the Black Death ended is unknown, it was likely a combination of quarantine, improved hygiene and migration away from disease centers. Because so many peasants and laborers died, the aftermath of the plague involved a cascade of social change and disruption. Peasants, now a rarer group, could and did demand better pay and treatment. Strangers, the Romany gypsies, Jews and others were often blamed for the Black Death and persecuted, especially during periods in which the plague returned to ravage Europe. Never again, however, did it take such a high toll of life.