First, they felt pain all over their body. Next, a lump — sometimes as small as pea, other times as big as an apple — protruded from their skin. Then, as the disease spread throughout their body, they coughed up blood . Finally — for many of them — came death. That was how people hundreds of years ago described the Black Death , which began sweeping across Europe in the 14th century, killing up to 60% of the continent’s population in one of the worst pandemics in human history. Today, many of us think of the plague as something confined to the history books — a grim symbol of the medieval period, before doctors knew about the existence of viruses or bacteria. But this month, three people in China were diagnosed with two different forms of plague , highlighting that while the plague is not as serious an issue as it once was, it’s also not entirely a thing of the past. Neither is debate about the cause of the disease, how it spread, and even where it came from. Plagued by ques...