Researchers: Rats Didn't Spread Black Death, Humans Did

concertina226 (2447056) writes "Scientists studying the human remains of plague victims found during excavations for London's new Crossrail train line have concluded that humans spread the Black Death rather than rats, a fact that could rewrite history books. University of Keele scientists, working together with Crossrail's lead archaeologist Jay Carver and osteologists from the Museum of London, analyzed the bones and teeth of 25 skeletons dug up by Crossrail. They found DNA of Yersinia pestis, which is responsible for the Black Death, on the teeth of some of the victims."

Comments

Old News

[wisnoskij]

Scientists discovered this at least 6 years ago when I watched a documentary about it, and most likely quite a bit before that.

Re:Old News

[Concerned Onlooker]

"the fact that some transmission was not by rats does NOT imply
that no transmission was done by rats."

What it DOES imply is that no matter who does the research or what the conclusion there is going to be disagreement from armchair scientists and contrarians on Slashdot.

actually, it was the fleas.

[somepunk]

Pneumonic plague being transmitted by air isn't news. It's a form of the disease that gets into your lungs, after all. Also, the primary vector isn't rats at all, but fleas, which often go directly from person to person.

The article's credibility is not helped at all when it mentions the plague virus, when it is actually caused by a bacterium.

Re:actually, it was the fleas.

[hey!]

Person who worked for years in arthropod borne disease control here.

Except for the reporting screw-up about virus vs. bacteria, this is all just quibbling. The reporters got it wrong as usual, but that doesn't mean that the researchers got it wrong.

Zoonotic diseases (ones that spills over from one animal population to another) always have fantastically complex life cycles. In epidemics of zoonotic diseases it's common for epizootic transmission (transmission between species) to be overtaken by enzootic transmission (transmission *within* a species). For example influenza is a bird pathogen that can cross over into mammalian species like swine and humans. If flu epidemics didn't shift gears from epizootic transmission (bird to human) to enzootic (human to human), they wouldn't be as big a deal. Just stay away from chickens.

So the idea that the black plague was primarily spread among humans enzootically is hardy groundbreaking epidemiology. It certainly doesn't mean that it's not dangerous to live in a place infested with plague-ridden rats. But the shift to enzootic transmission is something that's a bit different from the mosquito or tick borne diseases or occasional, isolated epizootic plague infections we're largely familiar with today.

It's a neat finding, in that it wasn't necessarily expected, but it makes sense in retrospect. In something like West Nile Virus, the natural focus of the pathogen is migratory bird populations that fly thousands of miles. But while a rat can hop on a ship and travel thousands of miles, the vast majority of rats spend their entire lives in a radius of a few hundred feet. Humans are much more mobile than rats; even if a few rats hitch a ride on a ship, they never go anywhere far *without* humans.

What's simplistic is the assumption there has to be only *one* factor involved in a zoonotic epidemic. Without epizootic transmission the plague would not have happened in the first place. That's not news. Without human-to-human enzootic transmission it would not have spread so widely or kill such a high percentage of the population. That is news (I guess -- I didn't work with people doing plauge so I have no direct knowledge of what people in that field thought). Of course before it becomes established science it's going to have to stand up to criticism for a few years.

Maybe

[dreamchaser]

The plague can take 3 forms, at least one of which, pneumonic, infects the lungs and spreads through the air, much like the common cold does. Just because humans had a role in helping to spread it doesn't leave the rats and their fleas off the hook. It is still quite likely that there were multiple vectors combined that caused the rapid spread of the disease.

Re:Virus? Plague?

[K. S. Kyosuke]

At the risk of sounding pretentious, that page doesn't list anything I haven't already known for years - in fact, anyone interested in the Black Death should be already aware of all these things.

We've known that some casualties were not bubonic but pneumonic cases, as well as that some were septicemic instead - even the contemporaries were aware of the three distinct forms of the disease, as manifested by their different symptoms, even if they misunderstood its bacterial underpinnings. We've also known that besides primary pneumonic plague (acquired through inhalation), there's secondary pneumonic plague that happens whenever Yersinia pestis spreads into a bubonic or septicemic plague victim's lungs through the bloodstream.

Claiming that we found out that "Rats Didn't Spread Black Death, Humans Did" feels like disingenous piece of reporting, though, because one of the hallmarks of pneumonic plague is its much more rapid onset and considerable lethality (about half the time it takes for bubonic plague to kill you, or something like that?). Within a town, it's entirely possible that the spread of pneumonic plague overtook bubonic plague whenever it got established, but the "spread" of Black Death was global, and the typical progress of pneumonic plague put it at a serious disadvantage when it came to long-distance travel (especially on ships). So chances are that in many, if not most places removed from other places (towns, regions, countries, continents), the primary pneumonic cases were "jumpstarted" by a case secondary pneumonic plague infection resulting from an infected flea bite. (At least, that's how I interpreted the smart books.)