Bubonic plague is still found in scattered locations around the world, but thanks to modern antibiotics it is far easier to treat than in the past. Yet, the disease may still have left its mark on humankind.
Under the microscope, Yersinia pestis doesn’t look particularly special. It’s a fairly standard shape for a bacterium – a sort of short, round-ended rod – and relatively immobile. But it is responsible for a disease that once wiped out a third of Europe’s population and caused millions of deaths around the world.
The very mention of the words bubonic plague tends to provoke both fear and fascination even today. The disease is now vanishingly rare in both the US and Europe, largely thanks to changes in lifestyles that prevent it from spreading to humans from infected fleas as easily. Even when it does occur, it can be relatively easily treated with antibiotics, saving lives. But cases still do occur.
Most recently, a man in Oregon in the US, caught the bubonic plague from his pet cat. It is not something that comes as an enormous surprise to evolutionary geneticist Paul Norman, who studies bubonic plague at the University of Colorado, Anschutz.
“There still are little pockets of plague in the US,” he says. It still circulates in wild animals such as squirrels and prairie dogs, he adds. On average, around seven cases of plague in humans are reported in the US each year, although deaths are far less common with just 14 between 2000-2020. In some parts of the world, such as Madagascar, the disease is more common.
But even though it is relatively rare compared to the past, the bubonic plague has left its mark on the human species and can still be found in the genomes of people living today.
Yersinia pestis is thought to have plagued the human species for thousands of years. DNA evidence of the bacteria has been found in skeletons dating back 4,000 years. But in the early 1300s, a strain of the bacteria exploded into Europe as the Black Death. It is thought to have originated in villages around the Chui Valley what is now Kyrgyzstan, perhaps passing through fleas from infected marmots into people before then spreading to Europe along the Silk Road trade route.