Since the Dark Ages, the human race has struggled against a very persistent disease: the bubonic plague. Known simply as the plague for much of human history, this illness has become significantly less dangerous as time has gone on and modern medicine has found new treatments for the once-deadly bacterial infection.
That doesn’t make stories of outbreaks any less scary, though. While the plague is little more than a shadow of its former self, history tells us just how dangerous it could be if we didn’t have such a good grasp on germ theory and medicine in the modern era. A recent outbreak among squirrels in California shows that there are still some echoes of the past being felt to this day.
In the Dark Ages, the Black Death was directly associated with rats. To this day, rats have a very negative reputation in Europe thanks to their role in spreading disease all over the world. However, the rats themselves aren’t the main vector for the illness: it’s the fleas they carry. Fleas are very tiny, wingless insects that survive by drinking blood from mammals.
Fleas hop onto rodents and catch a ride into human population centers, where they then hop off and bite humans on the ankles. These bites can contain the bacteria strain Yersinia pestis, the pathogen that causes the bubonic plague. While it’s technically possible to get the plague from handling infected animals, humans are much more likely to be bitten by a flea than to be sneezed on by a rat. Or, in the case of Californians, by a squirrel.
Some research also indicates that a major vector for the disease in the modern era is through cats and dogs. Since fleas like to bite these ubiquitous pet animals, it’s possible for humans to be infected when their pets sneeze or cough on them.
The outbreak in California has only affected a handful of humans, all of whom were given treatment at local hospitals and sent to recover at home. Thankfully, the days of the bubonic plague causing pandemic-level outbreaks are far behind us. However, in some parts of the world, like the Congo, Peru, and Madagascar still see periodic outbreaks of the disease cause loss of life on a small scale.
These outbreaks are troubling, however, because the disease appears to have become endemic to fleas and rodents who live in proximity to humans. Despite humanity battling the plague for centuries, we’ve never quite managed to wipe it out.