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Human Not Rat Parasites Were Responsible For The Black Death, New Research Finds

Boccaccio's 'The plague of Florence in 1348'. Wellcome blog post/Wikimedia Commons

Rats get a bad rap. They’re dirty and disease-ridden, they enjoy wallowing in garbage, and they just look plain sinister. But, thanks to new research, we can no longer blame them (or, indeed, gerbils) for the Black Death. Scientists from the universities of Oslo and Ferrara simulated outbreaks of plague in nine European cities and found the lice and fleas on humans (not rodents) were likely responsible for spreading the disease.

Europe had to endure several outbreaks of plague between the 14th and 19th centuries, the Black Death (1347-1351) being the most devastating. Within five years, the bubonic plague had killed an estimated 25 million people – or one-third of Europe's total population.


The disease-carrying parasites reached Europe from the Far and Near East via a fleet of Genoese trading ships. By the time they made it to port, most of the crew had perished and those still alive were on their deathbeds. At the time, Europeans (oblivious to the concept of bacteria) believed it was divine retribution.

Until now, the general assumption has been that rats (and their fleas) carried the bubonic plague through Europe. Research published in the Proceedings of the National Academy of Sciences undermines this theory, instead suggesting the spread can be "largely ascribed to human fleas and body lice".

The team ran three models of the disease outbreak, each involving a different vector or type of transmission: rats, airborne transmission, and human parasites. The final model was the best fit in seven out of the nine European cities studied. The researchers say that had rats been the culprit, the bubonic plague could not have spread so quickly.

"It would have to go through this extra loop of the rats, rather than being spread from person to person," Professor Nils Stenseth, a biologist at the University of Oslo, told BBC News.


Interestingly, their conclusion seems to support a first-hand account from the Italian poet, Giovanni Boccaccio, who wrote, “the mere touching of the clothes appeared to itself to communicate the malady to the toucher”.

While the study was completed for reasons of historical interest, it does have practical implications. The plague pathogen still lurks in Asia, Africa, and America and just last year, an outbreak of bubonic and pneumonic plague in Madagascar killed at least 202

“Understanding as much as possible about what goes on during an epidemic is always good if you are to reduce mortality [in the future]," Stenseth told BBC News.

The lesson here: good hygiene and limited contact with sick individuals is key to curbing a future outbreak. As for rats, they aren't entirely innocent. They may be off the hook this time but the critters are still carriers of plague pathogens, not to mention a whole host of other diseases.


[H/T: BBC News]


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