In 1348, Pope Clement VI’s physician wrote the following as the “Black Death” hit Avignon: “It was so contagious, especially that accompanied by spitting of blood, that not only by staying together, but even by looking at one another people caught it…The father did not visit his son, nor the son the father. Charity was dead and hope was crushed.” (From Deadly Companions by Dorothy H. Crawford)
Scientists have long suspected that the bacterium Yersinia pestis,which causes bubonic plague, caused the Black Death that killed over 30% of Europe’s population in 1347 and continued to burn through Europe for the next three hundred years. Two teams of scientists reported this week that not only was Yersinia pestis definitely the microbe that caused the Black Death, but that bubonic plague has its roots in China, where it has lived in fleas in the wild rodent populations for thousands of years. Humans are an accidental host of this deadly bacterium, but in three major waves it decimated the populations of Europe, Asia and Africa, causing the most dramatic fall in population ever recorded.
Y. pestis is carried by fleas, who are made ravenous by the bacteria and jump from rodent (often rats) to rodent looking for warm blood and injecting thousands of bacteria with each bite. As rats die, the fleas sense the cooling blood and jump to new victims. If the victim is human, they will probably be infected with bubonic plague and, if untreated with antibiotics (which they didn’t have during the middle ages), stand a pretty good chance of dying. If the infection goes to the victim’s lungs and they infect someone else by coughing on them, that person is as good as dead.
Bubonic plague eventually died out in Europe, but not before infected rats stowed away on ships traveling to the United States in the 1890s, where they arrived in San Francisco and quickly infected the squirrel population. Over 50 kinds of rodents in the Western U.S., Canada and Mexico are potential hosts for Y. pestisis and the bacteria is still surviving in these populations, from California to Colorado. Fortunately, as long as the disease stays in wild rodents and away from urban rat populations, it probably won’t cause many cases of plague in the U.S.A. (there were only 15 in 2006.) We’re lucky to live in the age of antibiotics, which can treat most cases of plague today.
What should you do if you don’t want to catch the “Black Death?” Avoid wild rodents like the plague.
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