Rats are Not to Blame for the Black Plague?!


Rats are Not to Blame for the Black Plague?!

Plague Preconceptions

In the early Middle Ages between 541 to 767 the bacterium Yersinia Pestis (aka the Black Plague, Black Death, or the Bubonic Plague) spread throughout Europe, yielding a hefty death toll. In the 14th Century, the plague resurfaced with a vengeance, claiming the lives of over 50 million. During the time, it was believed that the disease was caused by miasma, or “bad/poisonous airs” resulting from particularly foul smells.  It wasn’t until centuries later that another cause of the rapid spread of the plague was proposed: pests.

Initially, the theory was that rats alone were carrying and passing the disease themselves through bites, contact with their excrements, and simply living in close quarters with humans. As consideration of this theory progressed, it was discovered that the fleas on rats were most likely the true culprits of the historical pandemic. However, further exploration now suggests that rats may not actually be to blame for the spread of the plague.

The Study

A study regarding the simulation of plague outbreaks was published in a 2017 issue of the multidisciplinary science journal the Proceedings of the National Academy of Sciences. This study explored three different possible means of transmission including rats as vector-pests, airborne transmission, or fleas and ticks carried by human host to human host.

Based on the findings from tests outlining 9 different outbreaks, it was determined that the spread from fleas and ticks via humans was model that best fit the spreads. The results also showed that a spread caused by rats would’ve been very different from the actual progression of the epidemic. Co-author of the study and professor at the University of Oslo, Nils Stenseth, even stated that, “it would be unlikely to spread as fast as it did if it was transmitted by rats. It [the bacterium] would have to go through this extra loop of the rats, rather than being spread from person to person.”

In addition to the above findings, several researchers have stated that there is actually a lack of evidence supporting the theory that rats were involved in the initial cause of the outbreaks as well. “There is little historical and archaeological support for such a claim,” they explain, stating that rats succumb to the bacterium as well, therefore masses of dead rats would’ve been present during the outbreaks. As such, it is not entirely clear how the theory behind rats truly began.

The Plague Today

Unfortunately, the black plague is still around today. Thankfully, our modern medicine can now treat the bacteria if caught early enough, however it is still wise to be wary and careful. Professor Stenseth notes that this case of historical interest provides insight into cases of diseases today. “Understanding as much as possible about what goes on during an epidemic is always good if you are to reduce mortality in the future,” he explains, “our study suggests that to prevent future spread, hygiene is most important. It also suggests that if you’re [potentially] ill, you shouldn’t come into contact with too many people… So, if you’re sick, stay at home.”


Audoin-Rouzeau, F. (1999) [The Black Rat (Rattus rattus) and the Plague in Ancient and Medieval Western Europe]PubMed.gov. U.S. National Library of Medicine – The National Center for Biotechnology Information. Available at: https://pubmed.ncbi.nlm.nih.gov/11000955/ (Accessed: February 4, 2021).

Gill, V. (2018) Black Death ‘Spread by Humans Not Rats’BBC News. BBC. Available at: https://www.bbc.com/news/science-environment-42690577 (Accessed: February 12, 2021).

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Little, B. (2018) Rats Didn’t Spread the Black Death-It Was HumansHistory.com. A&E Television Networks. Available at: https://www.history.com/news/rats-didnt-spread-the-black-death-it-was-humans (Accessed: February 12, 2021).

McKinnon, M. (2018) Are Rats Innocent of Spreading the Black Plague?Smithsonian Magazine. The Smithsonian Institution. Available at: https://www.smithsonianmag.com/smart-news/are-rats-innocent-spreading-black-plague-180967855/ (Accessed: February 12, 2021).

Plague (2020) Centers for Disease Control and Prevention. The National Center for Emerging and Zoonotic Infectious Diseases and The Division of Vector-Borne Diseases. Available at: https://www.cdc.gov/plague/index.html (Accessed: January 27, 2021).

Plague (no date) World Health Organization. World Health Organization. Available at: https://www.who.int/health-topics/plague#tab=tab_1 (Accessed: February 4, 2021).

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