The biggest omission in this study about the propagation of the plague is the condition of humans in those years.
Too much fuss about "evolution" of bacteria and viruses -which by the way never happened- when the key is a mixture of a climate change and the weakness of humans in the transition.
It is a fact that human's health is challenged every Winter and this is the season when people acquire diseases, and when seasonal diseases spread out faster. Winter season is known as the time of catching a cold, the flu, and where these spread out when people sneeze and by touch.
How far Winter season affects the different kind of bacteria a and viruses is an important task in order to find out the Black Death.
So far, humans were weak under a small ice age which happened in the 14th century and in the centuries that followed it.
It is important to compare that temperature had influence with the propagation of this disease in those years.
Then, it was not a more powerful or "evolved" bacteria -which is nothing but mere fantasies after all- but a weakened human what caused a faster propagation of the disease.
Two great natural disasters struck Europe in the 14th Century. One was climatic: the Little Ice Age. This term is used in wildly varied ways by different authors, and there actually seem to have been two cooling episodes: an earlier one from the late 1200's to 1600 or so, and a later one in the 1700's and 1800's. During the earlier one, the Baltic Sea froze over in 1303, 1306 and 1307, something never before recorded. Alpine glaciers advanced. The Norse settlements in Greenland were cut off and grain cultivation ceased in Iceland. The last ship sailed from Iceland to Greenland in the early 1400's (tantalizingly close to Columbus); when contact was resumed in the 1700's, the settlements were long abandoned. Starvation, disease, raids by English pirates and conflict with natives have all been suggested as causes, and all probably played a role in the demise of the colonies. In France, crops failed after heavy rains in 1315; there were widespread famine, reports of cannibalism, and epidemics.
Carlos Le Baron.