3 Medieval and Modern Bubonic Plague: Some Clinical Continuities

In his book The Black Death transformed, Samuel K Cohn claims that the epidemic disease described in western European historical sources from AD 1347 to the midseventeenth century under the names plague, pestis, pestilence, plagen and the like must have been a disease other than the modern plague that reached Hong Kong in May 1894 from other parts of China, and later spread first to India and then to all inhabited continents. Alexandre Yersin showed that the disease in Hong Kong was caused by a bacterium, later named Yersinia pestis. It was also Yersin who claimed that he had found not only the cause of plague in China, but also the cause of the medieval and early modern plague epidemics. Four years after the discovery of the bacillus, Paul-Louis Simond proposed the transmission route from the rat (Rattus rattus) via the flea (Xenopsylla cheopis) to humans, although the scientific community was not fully convinced until ten years later, since this hypothesis did not explain all observations. The problems with the hypothesis were forgotten, which is easy to understand when we remember that the doctors and epidemiologists who were working in India at that time were facing a worsening and very serious epidemic. The simple preventive message to public health workers and the public was: exterminate the rats. The identification of medieval plague as the same disease as modern plague was accepted within thirty years, first by medical scientists and later by historians. Cohn writes, ‘‘Without argument, historians and scientists have taken the epidemiology of the modern plague and imposed it on the past, ignoring, denying, even changing contemporary testimony, both narrative and quantitative, when it conflicts with notions of how modern bubonic plague should behave.’’ I agree to some extent with Cohn’s criticism of how historians have imposed a modern understanding of plague epidemics in India on historical epidemics, and especially how historians have invented large populations of rats in the medieval towns and countryside of northern Europe without any support from contemporary historical sources or archaeology. However, I strongly disagree with his main point, which is that the medieval and modern plague epidemics must have involved