We Just Discovered the Black Plague Wasn't Actually Caused by Rats
Rats have been carrying the stigma of the Black Plague for over half a millennium, but it may turn out that they weren't the real culprits—in fact, dirty humans may be to blame.
The generally accepted story goes like this: rats aboard merchant ships brought infected fleas back to Europe from the Orient, and the fleas began spreading among the European populace, which hadn't figured out that bathing was a good thing to do every once in a while. The rats were the primary vector for the plague, and the pandemic killed about 30-60 percent of Europe's population.
The Black Plague (or Black Death) gets its name from the swollen black-and-blue buboes, or swollen areas, that showed up near lymph nodes on victims, especially around their groin and armpits. The initial symptoms of the disease included coughing, fever, and vomiting, but unlike a cold, death was the ultimate outcome: 80-90 percent of victims in medieval Europe died in less than two weeks.
However, recent research by the University of Oslo that modeled the spread of the disease using different transmission methods (including airborne transmission, rats, and human fleas/lice) found that the vector that explained the spread best wasn't rats—it was human ectoparasites (the fleas and lice).
This discovery may suggest that if humans had gotten rid of their own parasites, the spread of the Black Plague may have been much less devastating, regardless of rats. The research doesn't dispute that rats brought over fleas carrying the source of the plague (the bacteria Yersinia pestis), but their arrival didn't seal the fate of tens of millions of people.