For hundreds of years, the arrival of the bubonic plague in Europe in the mid-14th century has been blamed on rats. However, a new study released this week has put a different rodent under suspicion: gerbils.
Scientists at the University of Oslo in Norway have claimed that that the deadly disease was repeatedly brought to Europe from Asia via trade routes such as the Silk Road, and with gerbils, not rats as the carriers.
"If we're right," study co-author Nils Christian Stenseth told the BBC, "we'll have to rewrite that part of history."
The study examined over 7,700 tree ring records that revealed climate information about Europe during that period. They found that outbreaks in Europe occurred approximately 15 years after a spell of wet weather and warmer temperatures in Asia, which would have bolstered the gerbil and flea populations. By contrast, the timing of the outbreaks in Europe did not appear to coincide with any weather pattern on the continent.
Previously, black rats who had stowed away on merchant ships were thought to have enabled the plague to establish itself in Europe, with fleas spreading the bacteria by jumping from infected rat to humans. However, Stenseth told NPR that according to that theory, rats and their fleas should still be spreading plague in European cities today, when in fact, it has been nearly 300 years since a major outbreak.
The study theorizes that fleas carrying the plague bacterium jumped from gerbils to pack animals and humans, some of whom were traders who brought the disease to Europe. The next step is to analyze the DNA of plague bacteria, which can be found in the skeletons of its victims. If the Oslo theory is correct, the bacterial DNA would vary widely across each outbreak, as the disease would have likely changed each time it entered Europe.
Historians have estimated that the first outbreak of plague in medieval Europe, between 1346 and 1353, killed between 75 million and 200 million people, at least a third of the continent's population.