The outbreak of The Great Plague (BlackDeath) caused by humansIntroductionThe Black Deathwhich occurred in the 14th Century has killed one-third of the totalpopulation in Europe, and the bacterium (Yersinia pestis) living in rats were accused forthe spread of the disease for 700 years.
However, a research that carried outin 2017 claimed that human ectoparasites were more likely to have caused therapid spread of the disease than the rat flea, challenging the common conceptof spreading of the plague. SourceTheUniversity of Oslo and University of Ferrara’s researchers- KatharineR. Dean, FabienneKrauer, Lars Walløe, OleChristian Lingjærde, BarbaraBramanti, NilsChr. Stenseth, Boris V. Schmid reported through Proceedingsof National Academy of Sciences. BBC reported this news on the 16thJanuary 2018. MethodThe researchers digitalized publicly available data from 9localities that were affected by plague outbreaks.
Theydeveloped a Susceptible–infectious–recoveredmodel for the transmission of the plague. Each of thecities was broken down further into 3 groups- Human-Ectoparasite Model (fleasin human bodies and clothes), Pneumonic Plague Model (direct human-to-humantransmission) and Rat-Flea Model (rat fleas). They formed differentialequations for different groups, drew graphs and studied the mortality curves tofind the model which was most likely to cause the outbreak of the plaguehappened in different centuries. FindingsHuman fleas had the lowest BIC value in 7 out of 9 cities and theywere the quickest to spread the plague. Moreover, the difference between twoother models was more than 10, clearly out valuing and providing a strongevidence against rat flea and pneumonic concepts.
Therefore, human ectoparasitemodel is the most preferred model to describe the pattern and the spread ofplague transmission. ReliabilityThe researchers had divided 9 cities for reliability, however, theexperimental data is too small to represent entire Europe. Also, they neglectedthe common conditions that could have affected the death rate such as famine,immunity, and war. Moreover, they did not mix the transmission routes,preventing full description of plague contribution. The plague has occurredmany centuries ago so the accuracy of the research is impossible to be precise(e.g.
the number of rats). Furthermore, Monica H. Green, a historian at ArizonaState University claimed that this research has minimized the probability ofairborne transmission of disease by humans. On the other hand, Nils Stenseth, a professor at the University ofOslo said that the spread of plague was too rapid if the rats were the cause.Not only the number of dead rats was lacking which should have been significantbut also the rats should have been influenced by the plague first before thehumans, not the other way round if they were the main reason of the plague.