Sean Martin in his book, The Black Death, provides many interesting details about the terrible pandemic of the 1340s. However, I came away from the book questioning just how sure we can be that we know what caused The Black Death.
The routine story goes like this: the Black Death was caused by a bacillus (not discovered until the 1890s) called Yersinia pestis. This bacillus lives in the bloodstream of small rodents. These rodents carry fleas, such as the Xenopsylla cheopsis, which feed on the blood of the rodents. We today assume that the plague was thus transferred to humans when fleas of infected rats bit humans.
However, the supposed main “vector” (disease-spreader) of the Black Death, the X. cheopsis flea, doesn’t even like the taste of humans. The justification for assigning the flea top vector status is that, as the rat population died-out in a certain location due to the disease, the flea would be forced to hold its nose, if I may speak figuratively, and partake of human blood.
Furthermore, Martin tells us that the symptoms of the plague studied in the 1890s differed “markedly” from those known to be associated with the Black Death. Contrary to the accepted story, there really is no justification to declare absolutely that the Black Death of the 1340s was the same disease studied in the 1890s.
Many people think of the Black Death as another name for the “Bubonic Plague.” However, according to Martin, the Bubonic Plague was just one of three types of the 1340s pandemic, the type associated with the unsightly and painful boil or “buboe” that a victim developed in his or her groin, armpit, or neck (Martin informs us that boubon is Greek for groin). Usually, only one boil would appear. It is estimated that the kill rate of those infected was something around 60% from this version of the plague. The Bubonic Plague infected a person’s lymphatic system.
There were also two other manifestations of the 1340s epidemic. The second, Pneumonic Plague, infected the lungs. The type of the plague was airborne and spreadable by coughing or sneezing; thus it was the most contagious of the three types. The mortality rate for victims of Pneumonic Plague is thought to have been over 95%.
The third variety of plague in the 1340s was the Septicaemic Plague, which infected the bloodstream. It was transferrable by the species of flea which normally feeds on humans, the Pulex irritans. However, it is questionable whether the P. irritans could have actually sucked-up enough blood to transfer a fatal dosage of the disease to its next host.
Historians and medical-types today claim that the Black Death was a mixture of all three varieties of the plague, presumably all from the same source, the Yersinia pestis bacillus spread by rat-fleas.