Gerbils and not rats may have been the cause of the plague, claims study

Black rats have long been considered the carriers of the Black Death that arrived in Europe in the 14th century, but a new study suggests that the culprit may have been gerbils from Asia.

In a study published in the Proceedings of the National Academy of Sciences, researchers looked at the 1347 outbreak when the disease came to Europe from Asia, killing an estimated 75 million people.

Examining tree rings, the scientists found that weather conditions were not optimum for a large rat infestation, which “would need warm summers, with not too much precipitation”. Instead, the conditions in Asia appear to have been right for the giant gerbil, a rodent species native to the continent, to have thrived.

A wet spring followed by a hot summer would have caused the number of gerbils and fleas to have swelled, say the scientists, with infected gerbils likely making their way to Europe via the silk road.

The waves of Black Death that proceeded to infect European population over the next 500 years were thought to have been the result of climatic changes and the size of the rat population, but it appears that in each case the plague may have died out in Europe, but gone back to Asia.

To test this theory further, the scientists now plan to test plague bacteria DNA from ancient skeletons across Europe. If the DNA shows a large amount of variation from each outbreak, it would imply that the plague had not remained in a European rat reservoir, but evolved in a rodent population in Asia and then travelled time and again to Europe.