The Plague Has Been Around Longer Than You Probably Thought

The effects of the bubonic plague, also known as the "black death," are perhaps best understood by its effect on 14th century Europe, Asia, and Africa. Plague doctors patrolled the streets of European towns and cities, vainly applying the ancient yet accepted theory of humors to treat victims. By the time the plague had begun to taper off, it had claimed the lives of 200 million people across the world, and even then it continued to kill millions in smaller intervals for centuries after (via History.com). 

While deadliest from 1346 to 1352, the comparatively less deadly outbreaks of previous centuries are thought to have also been the work of this ailment. The Antonine and Justinian plagues for instance, which killed millions in ancient Rome, are believed to have been instances of the bubonic plague reaching Europe via the Silk Road or overseas trade. The earlier Greek Plague of Athens may have been an example of the disease as well, though other causes are equally entertained (via Ranker). Yet as the Smithsonian reports, the bubonic plague's earliest infections may have predated even all of these events by thousands of years. 

Bubonic plague spreads via a bacteria known as Yersinia pestis, which according to the WHO is commonly found in fleas. The spread of these fleas is enabled by the rats they infest, jumping to new hosts whenever they get the chance and thus introducing them to the bacteria. While this mode of transmission is often attributed to close proximity within urban areas, genetic examination of 5,000-year-old human remains revealed that Yersinia pestis was capable of infecting humans even before the construction of major cities in Europe.

However while infection would have been disastrous for individuals, the lack of certain genes within the bacteria that were present in the medieval-era plague leaves researchers unconvinced that it was capable of spreading quickly (via BBC). As none of the ancient victim's three compatriots were infected, and more broadly there is a lack of any mass graves that date to this period, the notion of large epidemics among hunter-gatherers is currently theoretical at best.