The plague — which in the mid-14th century was also known as the Black Death — devastated swaths of Europe, killing millions in under a decade.
One of the puzzles surrounding this ancient pandemic was how it spread so quickly.
The common wisdom is that rat fleas were the big spreaders. But now a new paper is making a second parasite look like it may have helped play a role in plague transmission — the lowly human body louse.
The disease is caused by a bacterium called Yersinia pestis. Once the bacteria enters the skin, they travel to a nearby lymph node — in your armpit, groin or neck, say — and multiply. The lymph node swells and inflames, becoming what’s called a bubo (hence the term “bubonic plague”). From there, the bacteria usually break out into the bloodstream where they cause severe infection. “And that’s always life-threatening,” says Joe Hinnebusch, a microbiologist now retired from the NIH’s National Institute of Allergy and Infectious Diseases. Sometimes, “plague can spread from the bloodstream and infect the lungs, causing pneumonia.” This form develops rapidly and is usually fatal. It can also be transmitted between people when someone coughs or spews infected droplets.