While it is commonly assumed that rats and their fleas spread plague during the Second Pandemic, there is little historical and archaeological support for such a claim.
‘The Black Death pandemic, caused by the bacterium Yersinia pestis and often referred to simply as “plague,” was spread by human fleas and body lice, and not similar parasites found on rats.’
Using Bayesian inference, a research team found that human ectoparasites, like body lice and human fleas, might be more likely than rats to have caused the rapidly developing epidemics
in pre-Industrial Europe. Such an alternative transmission route explains many of the notable epidemiological differences between historical and modern plague epidemics.
were observed in the spread of the plaque as the commonly accepted mode of transmission does not fit with the historical evidence. One such disconnect is that records from the first outbreak do not mention a large number of rats dying off, like it was observed and recorded in the later outbreak in Europe during the 19th century.
This has led experts to speculate that human parasites
played a huge role in the pandemic. And that speculation is that fleas and lice could have fed on infected humans, and then transmitted the disease to other humans.
In the study, mathematical equations were used to create three different models of plague transmission during a series of outbreaks in Europe called the second pandemic
, which includes the Black Death and occurred during the 14th through 19th centuries.
One model states that the disease was spread from rats to fleas to people; a second model states that the disease was spread from human fleas and body lice to other people; and a third model claims that the disease was spread from person to person through the air
, which occurs only when people develop a form of plague known as pneumonic plague.
Historical data on plaque deaths in nine regions during the second pandemic point to human parasite model which may best reflect the death rates in seven of the nine regions, compared with the other two models.
"Overall, our results suggest that plague transmission in European epidemics occurred predominantly through human [parasites], rather than commensal rat or pneumonic transmission," the research team reported in their paper.
The complete research is published in the Proceedings of the National Academy of Sciences