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  • [♪ INTRO]

  • In the 14th century, the Black Death spread throughout the old world, wiping out somewhere

  • between a quarter and half of all the people living in Eurasia at the time.

  • And that put the plague right up there with smallpox as one of the deadliest diseases

  • our species has ever faced.

  • But, of course, nobody gets smallpox any more.

  • Literally nobody: it's been eradicated.

  • You would think the Black Death is one of those diseases left in the dustbin of history, too.

  • But the plague is alive and well, and while it's not causing

  • world-changing epidemics any more, it's still a problem.

  • It turns out we're still learning a lot about this infamous bacterium, and the new

  • intel might help scientists determine if it will ever go all medieval on us again.

  • The plague is caused by the bacterium Yersinia pestis.

  • It evolved from a mild gut bug sometime in the last ten thousand years.

  • And it's been plaguing us since at least 541 CE, when it picked up a mutated version

  • of a gene called Pla, a protein-cutting enzyme that allowed it to infect more of the body

  • and spread more virulently than its older cousin.

  • Now, there are actually three types of plague.

  • Bubonic plague is when it infects the lymph nodes,

  • causing them to swell up as painful buboes.

  • If the infection spreads to the bloodstream, it becomes septicemic plague.

  • But the form of most concern to public health professionals is pneumonic plague,

  • which is when it infects the respiratory tract.

  • It's more deadly than the other forms, and it can more easily spread from person to person

  • directly because infected people send bacteria-filled droplets into the air when they cough.

  • And that's a big deal because usually, the bacteria move around

  • thanks to the help of other critters, called vectors.

  • The plague is a zoonotic disease, meaning it can spread between humans and animals.

  • And while rats are usually blamed for the spread of plague, the actual vectors are biting

  • parasites like fleas, which carry the bacteria in their guts.

  • In fact, a study in January of 2018 suggested that the fleas and lice which

  • spread the Black Death may have mostly been dining on humans

  • rather than frequently jumping between rodents and people.

  • But rodents can get the plague and act as carriers,

  • meaning it can hide in their population while it's not infecting us,

  • something that definitely did happen back then, and still happens now.

  • Fortunately, all forms of the plague are treatable with antibiotics.

  • The challenge is catching it in time, since its early symptoms often resemble the flu.

  • And doctors, well, when they see flu-like symptoms,

  • they guessflubefore they guessthe actual, literal plague.”

  • So could the plague ever mount a Michael Jordan-style comeback?

  • Well, for people in some parts of the world, “backis the wrong word.

  • The plague is native to parts of North and South America, Africa, and Asia.

  • And though it isn't wiping out a third of the world's population like it used to,

  • it does still cause serious outbreaks in places like Madagascar,

  • and there are a couple thousand cases reported every year.

  • And that's in part because of those furry carriers.

  • It's neither feasible nor desirable to wipe out all the animal reservoirs the plague can hide in.

  • Like rats. And ferrets. And cute little kitties.

  • And unlike with smallpox, good plague vaccines don't exist.

  • At least one promising one is in development, but prior to that,

  • existing vaccines could cause nasty reactions, had to be re-upped frequently,

  • and they didn't really work very well anyway.

  • A real triple crown.

  • Even today, scientists are still unlocking the plague's nasty little secrets.

  • It wasn't until 2015 that a study published in PLOS Pathogens described how the bacterium

  • could make its way from a tiny, shallow flea bite to your lymph nodes.

  • Since it's still around, the short answer is yes, the plague could rise again.

  • Luckily, modern hygiene and clinical practices generally keep it in check.

  • We're usually able to get anyone who's coughing up plague-laced sputum off the street

  • before they encounter too many other people.

  • So person-to-person transmission has become blessedly rare.

  • And we don't tend to interact so much with flea-infested animals.

  • But the real game-changer has been those antibiotics.

  • And that's where the potential for a modern outbreak becomes a little more of a reality.

  • See, in 1995, researchers raised red flags over the discovery of strains of the plague

  • that were resistant to some antibiotics, which would make for an extremely deadly outbreak

  • and is therefore a perfectly reasonable thing to raise red flags over.

  • However, these drug-resistant strains haven't caused much trouble yet.

  • That's partially because it actually seems to be difficult for the

  • plague bacterium to acquire antibiotic resistance.

  • Drug resistance is often transmitted among bacteria on

  • small, circular snippets of DNA called plasmids.

  • Plague bacteria have to pick up these resistance-conferring plasmids from another bacteria, but they just

  • don't seem to run into resistant bugs that often in nature.

  • And unlike humans, rodent populations don't frequently encounter antibiotics.

  • So there doesn't seem to be an evolutionary advantage ensuring that the plague bacteria

  • will hang on to drug resistance even if they do pick it up.

  • But, if there was to be a global pandemic, it would most likely be from a resistant strain,

  • or from one modified for bioterrorism.

  • There's actually a really long history of using the plague as a weapon.

  • Armies used to catapult corpses over the walls during sieges to help thin the defenses.

  • But doctors, scientists, and military personnel have plans in place in case anyone

  • does try to modernize that strategy.

  • And anyone who would even consider such a thing would be

  • violating several international agreements.

  • Short of these two scenarios, a 21st-century Black Death-like epidemic is pretty unlikely.

  • That doesn't mean the plague isn't a problem for the

  • thousands of people who do catch it every year.

  • But fortunately, by developing better vaccines and continuing to study the bacterium responsible,

  • we're working on beating it back for good.

  • Thanks for watching this episode of SciShow!

  • If you enjoyed learning about the Black Death, you might like our episode about

  • how it and five other diseases totally changed the course of human history.

  • [♪ OUTRO]

[♪ INTRO]

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瘟疫会不会再次兴起(Could the Plague Rise Again?)

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    joey joey 發佈於 2021 年 06 月 04 日
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