Posted on 01/15/2018 6:21:35 PM PST by nickcarraway
A provocative new study suggests that medieval plagues spread via fleas and lice on people.
Rats have long been blamed for spreading the parasites that transmitted plague throughout medieval Europe and Asia, killing millions of people. Now, a provocative new study has modeled these long-ago outbreaks and suggests that the maligned rodents may not be the culprits after all.
The study, published on Monday in the journal PNAS, instead points the finger at human parasites—such as fleas and body lice—for primarily spreading plague bacteria during the Second Pandemic, a series of devastating outbreaks that spanned from the 1300s to the early 1800s.
These outbreaks include the infamous Black Death, which wiped out a third of Europe’s population in the mid-1300s, amassing a body count in the tens of millions.
“The plague really transformed human history, so it’s really important to understand how it was spreading and why it was spreading so fast,” says lead study author Katharine Dean, a doctoral research fellow at the University of Oslo’s Centre for Ecological and Evolutionary Synthesis.
DEADLY BITE
When fleas infected with the bacterium Yersinia pestis bite humans, the bacteria can jump into the bloodstream and congregate in humans’ lymph nodes, which are found throughout the body. The infection causes lymph nodes to swell into ghastly “buboes,” the namesakes for bubonic plague. (Find out how plague bacteria evolved.)
In cases of plague since the late 1800s—including an outbreak in Madagascar in 2017—rats and other rodents helped spread the disease. If Y. pestis infects rats, the bacterium can pass to fleas that drink the rodents’ blood. When a plague-stricken rat dies, its parasites abandon the corpse and may go on to bite humans.
Because of rats’ role in modern plagues, as well as genetic evidence that medieval plague victims died of Y. pestis, many experts think that rats also spread plague during the Second Pandemic.
In 1986, archaeologists uncovered a mass grave in East Smithfield, London, used to bury victims of the Black Death in the 1340s. At the time, one observer said that 200 victims of the plague were being buried each day. PHOTOGRAPH BY MOLA/GETTY But some historians argue that the Black Death may have spread differently. For one, the Black Death tore through Europe far faster than any modern plague outbreaks. In addition, “rat falls” precede some modern outbreaks, but medieval plague records don’t mention rats dying en masse.
“Geneticists and modern historians were putting the rat into the position [of spreading the plague] and were straining bits of evidence,” says Samuel Cohn, a University of Glasgow medieval historian who has criticized the rat-flea theory.
As an alternative, some scholars have long toyed with the idea that fleas on humans spread the Black Death. If fleas and lice picked up the plague by biting an infected human, they could potentially hop onto a person in close quarters and transmit the disease.
Mathematically, the patterns in how disease moves through a population are different for the rat-flea and human-parasite modes of transmission. To put them to the test, Dean’s team modeled each with equations that simulated the rise and fall of an outbreak, based on how rats, fleas, and body lice would behave and spread plague.
“It’s basically bookkeeping—you see how people move [in the simulation],” says coauthor Boris Valentijn Schmid, a University of Oslo computational biologist and Dean’s Ph.D. adviser.
After running their models many times, Dean and Schmid statistically evaluated which models best matched mortality patterns from nine different European plague outbreaks from the Second Pandemic. To their surprise, they found that in seven of the nine cities they examined, the human-parasite model more closely fit mortality records than the rat-flea model.
“It’s a really cool piece of work,” says Charles “Chick” Macal, a systems scientist at Argonne National Laboratory who models the spread of diseases but wasn’t involved with this study. “It gets at the underlying question of why these outbreaks occur at all.”
Dean and Schmid say that there’s room to improve their models with more experimental data. They also acknowledge that their study is likely going to stir controversy among plague scholars, some of whom passionately argue that rats caused the medieval outbreaks.
“In plague, there’s a lot of hot debate,” says Dean, who sees herself and Schmid as more objective observers in this case. “We have no dogs in this fight.”
Several additional factors made the situation worse. Because of the witchcraft fears cats were killed in a number of areas in Europe. The rats at the time were not the gray Norway rat which lives in cellars and sewers, but the black and brown rats which were upstairs rats. Some time ago I read that plague is endemic in 17 US western states, often in the prairie dog population. A few people catch it here every year. Also, while the bubonic form is the most common and more recoverable, there is the pneumonic form which can be spread by coughing and sneezing and like the septisemic form is almost always fatal. This may be why the death rate was so high in some epidemics.
I recently read that marriages were often held in June because people had their annual bath when it got warm in may and were not yet “ripe.” I am sure that many a couple shared their vermin on a regular basis. My husband once came home from a trip where he stayed in a hostel. We took 23 lice off his body. He was very hairy. He was afraid I would think he had been fooling around on his trip, but most of the lice were in his chest hair and even one in his eyebrow, not below the belt. Fortunately, I noticed one of them before we got lovey dovey, so began the careful search. We also got scabies once, hugging a friend who had returned from Russia (with love??). Then the kids got it, we would launder everything, then they would wear a jacket that had fallen behind the couch. and get them again. Took 6 months and much laundering to end that epidemic.
Perfume was invented to cover up the stench of body odor, and since not all marriages were done after the yearly bath, flowers were incorporated into the ceremony to help mask the smell of the bride.
I’m thankful for clean hot water on demand!
That rumor was started by cats......
That rules out Hillary
It's not a new problem, either in food (strong spices, salting, smoking) or in personal relations. The ancient world stunk to high heaven of dung because, well, hygiene practices. Still that way in arid countries.
A disinformation campaign by cats.
Who would have thought?
The link says it is not on this server 404. ?
Thank you for the link, it works.
I may need some understanding, as science is NOT my best subject. I thought it was the fleas, on the rats, that actually caused the Black Death because they could transfer and bite, even if rat was dead?
I will read the article, and if I have questions I will get back to you.
Thanks again.
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