The Black Death of the 1340s and 1350s was, in terms of the percentage of the population lost, the worst recorded plague in human history. It wiped out as much as a quarter of the world’s population, probably including more than half the population of Europe, and records suggest that it sometimes did so in a spectacularly gruesome way—routinely covering its victims in exploding cysts and rotting their extremities with gangrene. It was the pneumonia and not these more visible symptoms that killed most victims, but all told, it was a terrible way to die. The grief and horror that survivors must have felt would have been enough to break anyone’s heart, and that’s essentially where Europe was in these years leading up to the Renaissance—a grieving, terrified, brokenhearted continent.
This 2011 report from Nature magazine provides a good overview of everything we knew, until very recently, about the Black Death:
You’ll notice the rats. By way of their fleas, rats—it has long been reasoned—carried the bubonic plague (yersinia pestis), and the theory was that if you got rid of the rats, you wouldn’t have another plague outbreak. But that theory has never fully explained how quickly and universally the plague spread, and now scientists at Public Heath England have an alternative explanation: based on an examination of plague victims from 14th-century London, they say that the plague was airborne and that rats had very little to do with its spread.
Whether this new theory holds water or not, industrialized nations have little to fear from yersinia pestis today—contemporaneous evidence suggests that almost the entire population of Europe was effectively immunocompromised due to poor diet, malnutrition, and existing infections, rendering them more vulnerable to the disease than the vast majority of people reading this would be. But people in rural areas of developing nations who do not have immediate access to antibiotics and other effective forms of medical treatment are still vulnerable, and a variant of the original Black Plague is still taking lives in Madagascar’s villages to this day. For the residents of these villages, and for the millions of 14th-century victims who preceded them, our relative safety is of no help.