Demographic Crises
Theories of the Disease
The descriptions are detailed and depressing, aren't they? They're also distressing, for they seem to describe different diseases. At least, modern medical science knows of no one disease that exhibits all the symptoms described (and there are many other descriptions), and is virulent both in summer and in winter, and has such a high mortality rate.
Without entering into the controversies, there are three basic interpretations, each with variations. First, that the Black Death was the bubonic plague supplemented by localized outbreaks of septicaemic and/or pneumonic plague. The second theory says the Black Death wasn't plague at all but was some other disease such as anthrax. The third interpretation isn't really an argument but merely posits "another" cause. Candidates include a hitherto-unknown disease brought by a comet or meteor strike, or a genetic mutation in an existing virus or bacterium.
The plain fact is that no interpretation is without its weak points. I find it significant that the adherents of the "bubonic plague plus" theory are mostly historians, while the principal critics of this are members of the medical profession. I also find it frustrating that none of the arguments address later outbreaks. As you will see, the Black Death was by no means ended by 1350 but it returned frequently though with less devastation. I cannot find anyone who goes through the volumes of evidence on later plagues to discuss whether those outbreaks were bubonic or anthrax or what.
Perhaps because I'm a historian, I continue to hold to the bubonic-plus theory as described by Robert Gottfried. The criticisms raised by Cohn and others are significant and interesting, but they don't look beyond the initial outbreak and they don't offer a convincing alternative. The rest of this essay is predicated on the traditional interpretation.