Black rats may not be the culprit behind numerous outbreaks of the bubonic plague across Europe centuries ago, a new study suggests.
Scientists believe repeat epidemics of the Black Death, which first began in Europe in the mid-14th Century, instead trace back to gerbils from Asia.
Prof. Nils Christian Stenseth, from the University of Oslo, said “If we’re right, we’ll have to rewrite that part of history.”
The study was published in the Proceedings of the National Academy of Sciences.
The Black Death, which originated in Asia, arrived in Europe in 1347 and spawned one of the deadliest outbreaks in the history of humans. Over the next 400 years, epidemics continued to outbreak, killing millions of people.
It had been largely thought that black rats were responsible for the establishment of the bubonic plague in Europe, with new outbreaks occurring when fleas jumped from infected rodents to humans.
However, Prof Stenseth and his colleagues think the black rat should be exonerated from this supposed crime.
They compared tree-ring records with Europe from 7,711 historical plague outbreaks to see if the weather conditions would have been consistent for a rat-driven outbreak.
He said: “For this, you would need warm summers, with not too much precipitation. Dry, but not too dry.”
“And we have looked at the broad spectrum of climatic indices, and there is no relationship between the appearance of plague and the weather.”
Instead Prof. Stenseth and team believe that specific weather conditions in Asia may have caused another plague-carrying rodent – the giant gerbil – to thrive. They believe this then later led to epidemics in Europe.
“We show that wherever there were good conditions for gerbils and fleas in central Asia, some years later the bacteria shows up in harbor cities in Europe and then spreads across the continent,” Prof Stenseth said.
He said that a wet spring followed by a warm summer could have sent gerbil numbers soaring.
“Such conditions are good for gerbils. It means a high gerbil population across huge areas and that is good for the plague,” he added.
The bubonic plague died out in Europe after the 19th Century, however outbreaks continue to this day in other regions of the world of different plagues.
The World Health Organization said there were nearly 800 cases reported worldwide in 2013, resulting in 126 deaths.