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Hey Vsauce, I'm Jake and in the incredible[br]game The Last of Us 60% of the global population,

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4.25 billion people, more than the entirety[br]of Asia, have suddenly ceased to exist or

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are just no longer people. And scenarios like[br]this are nothing new, there have been hundreds

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and hundreds of movies and videogames that[br]cover similar events, but could a pandemic

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like what is depicted in The Last of Us...actually[br]happen?

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You only have to go back 95 years to 1918,[br]at the end of World War 1, to witness one

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of the most deadly and disastrous pandemics[br]in human history: The Spanish Flu.

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This variety of avian influenza killed an[br]estimated 50 to 100 million people, more than

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3 times the amount who died in the actual[br]war, and with a worldwide population at the

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time of 1.85 billion, it wiped out 3-5% of[br]the entire planet; and that was only in one

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year.

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But the flu is a virus that actually exists,[br]and in the work of fiction The Last of Us

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we are dealing with an organism, a fungus...that[br]also...actually exists.

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Cordyceps are fungal parasites that infect[br]and take over insects. The most well known

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being ophiocordyceps unilateralis that infects[br]ants, turning them into zombies. A spore from

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the fungus enters the ant's body, taking over[br]its brain and controlling its movements. Not

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too long after, the ant finds a perfect spot[br]to die, the fruiting body of the fungus grows

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out of the ant's head, and a slew of spores[br]are released onto the unsuspecting ant population.

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It has been known to decimate entire colonies,[br]but luckily it only infects insects, and it's

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not like diseases can move from one species[br]to another...well....

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An estimated 60% of all modern diseases came[br]from animals, specifically ones that we live

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in close contact with or have domesticated.[br]From cattle grew measles, tuberculosis and

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smallpox. From pigs and birds we have the[br]flu. From chimpanzees we have AIDS. All of

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these started out as infections that couldn't[br]be spread to humans, but after years and years

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of these microbes being around us, they adapted[br]to our biology.

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But we don't live in direct contact with ants,[br]and most people don't eat ants, so that's

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good...but other animals do, and then other[br]animals eat those animals, and at some point

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on this parasitic food chain lie humans. Considering how diseases mutated and progressed from domesticated

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animals to us, it isn't too far fetched to[br]think that a fungal infection like this, whose

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only purpose is to survive long enough to[br]spread, could adapt and evolve to lay claim

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to the top of that food chain.

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A great example of a microbe's ingenuity is[br]in Jared Diamond's amazing book 'Guns, Germs

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and Steel'. Jared talks about the bacterial[br]disease typhus and how it was transmitted

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to people by going from rat fleas to rats[br]to humans. But after a while, typhus figured

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out a much easier way to infect us: by cutting[br]out the unnecessary carriers and going directly

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from human body lice to humans.

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If a fungal parasite like the Cordycep could[br]infect humans like it does in The Last of

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Us, how long would it take? One of the biggest[br]differences between the Spanish Flu in 1918

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and a modern day pandemic is how connected[br]we are. What would have taken two weeks to

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go from New York to Germany by boat, can be[br]done in 8hrs on a plane. Using the Global

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Epidemic and Mobility software and some parameters we know from the game, we can create a model

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and simulate what the transmission and spread[br]would look like.

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In about 60 days, the fungal parasite would[br]have infected the majority of the planet.

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And you know things are bad when not even[br]Madagascar is safe.

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But that isn't to say that the governments[br]of the world don't have plans in place. Most

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governments - and the United States in particular[br]- have strategies for biological threats,

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counterterrorism, and the one that applies[br]to this situation most, The National Strategy

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for Pandemic Influenza. In it their high estimate[br]for fatality domestically is 2 million, or

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less than 1% the population of the US. This[br]incredibly detailed 233 page document really

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drives home one main point, and that is "sustain[br]infrastructure and mitigate impact to the

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economy and the functioning of society".

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A virus or disease or parasite doesn't affect[br]power lines, cars, the internet...it affects

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the people who make those things work. When[br]60% of the entire population, over 4 billion

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people, just stop being - when the doctors,[br]the teachers, the mechanics, the mail men

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vanish, and what we know as society crumbles...all[br]that's left is...the last of us.

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And as always, thanks for watching.

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