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IT WASN’T the rats after all. Cute little gerbils, not their much-despised cousins, may have caused the Black Death in Europe in 1347, as well as prompting repeated outbreaks of plague over the next four centuries.
Plague is caused by the Yersinia pestis bacterium, which is carried by fleas and mostly affects rodents. Europe has been hit by plague a number of times, but the second pandemic – the one that caused the Black Death – is the most notorious.
The disease is believed to have originally arrived in Europe from Asia via the Silk Road trading route. But the repeated outbreaks from the Black Death onwards have been blamed on rat reservoirs in Europe: bacteria-infested fleas hiding out in rats.
But Nils Christian Stenseth at the University of Oslo, Norway, and colleagues say that instead of rats, their furry counterparts – probably gerbils and marmots – in central Asia were to blame.
The team analysed 4119 post-Black Death plague outbreaks and found that the vast majority probably spread from outbreaks nearby. But Stenseth identified 61 separate outbreaks that took place in 17 harbour areas, including London and Hamburg, that are likely to have been caused by maritime imports from Asia.
By comparing these cases with historical records, Stenseth’s team was able to identify 16 years in which brand new introductions of Y. pestis were probably responsible for plague outbreaks, as opposed to infection from neighbouring regions.
They found that climate fluctuations in Asia – above average temperatures followed by sudden drops – consistently preceded plague reintroductions in Europe (PNAS, DOI: 10.1073/pnas.1412887112). This could be because, under warmer conditions, fleas become more active and the rodents they live on more numerous. When the temperature drops, rodent populations crash and the fleas are forced to find new hosts.
Climate fluctuations are likely to affect wildlife plague reservoirs today, too, says Stenseth. “In central Asia and northern China, the current climate change is likely to increase the occurrence of plague, whereas in the southern part of China it is likely to decrease.”
This article appeared in print under the headline “Gerbils and Silk Road to blame for the plague”