Marseille during the Great Plague of 1720. A study of mortality records for the Black Death in nine European cities seems to indicate human lice and fleas spread the disease. (Michel Serre/Musée des Beaux Arts Marseille)
The Black Death, which killed thousands throughout Europe in a pandemic stretching from the 14th to 19th centuries, was likely spread by parasites such as fleas and lice carried on the human body.
While rats have long been blamed for spreading the fatal disease throughout Europe, researchers at the University of Oslo in Norway and the University of Ferrara in Italy now believe humans and their parasites were the biggest carriers.
“There are so many questions that this pandemic raises and how it spread so quickly is one of them,” said Katharine R. Dean, lead author on a paper published Monday in the journal Proceedings in the National Academy of Sciences,
Dean and her colleagues studied nine outbreaks of the plague from 1348 to 1813 in European cities, including Barcelona, Florence, London, Stockholm, Moscow and Gdansk, Poland. A total of 125,000 people died in those outbreaks, sometimes so quickly that they could not be buried properly.
The bacteria killing them was Yersinia pestis, called bubonic plague or the Black Death, and it resulted in three significant plague periods in Europe.
Second Pandemic outbreaks
The period of the 14th to the 19th centuries, the time of the Second Pandemic, was the focus because there are fairly reliable official records of death rates as well as contemporary descriptions of the disease, Dean said.
An archaeologist works on March 10, 2015, at the site where eight mass graves with more than 200 skeletons were found under the Monoprix Reaumur Sebastopol store in Paris. Experts believe they are victims of an outbreak of bubonic plague in the Middle Ages. (Philippe Wojazer/Reuters)
The First or Justinian Pandemic in 541-544 was too early to result in accurate records.
Nor are rats blameless — they are believed to be carriers of the disease in the Third Pandemic, starting in 1855, Dean said. But that plague was accompanied by “rat falls,” or mass deaths of rattus rattus in the streets.
The rapid spread of Yersinia pestis in the Second Pandemic is considered mysterious, said Dean, who is a PhD researcher interested in infectious disease epidemiology.
Tales from the Conspiratum 