Why Do Other Animals Keep Giving Us Viruses?

published on July 9, 2020

A typical virus is only about 100 billionthsof a meter acrossIf all of the viruses on earth were laid end-to-end,how far do you think that chain of germs wouldstretch?Tens of millions of meters?Tens of millions of kilometers?The answer is tens of millions of light yearsThere are a LOT of viruses out there

And that is a scary thoughtBut!Viruses are cellular parasitesThey can't survive unless they are insidethe cells of some other living thingAnd without these cells to call home, thatchain of germs would disappearPlants, fungi, animals: Every living specieson Earth today is home to its own universe

Of virusesBut more and more, viruses are jumping outof other animals and into us, and making usvery, very sickWhy?The answer to that tells us something veryimportant about our place in natureAnd it makes one thing really clear: Virusesaren’t out to get us

We go out and get themHey smart people, Joe hereOver the past few months, everyone’s beentalking about what’s happening right nowwith SARS-CoV-2But SARS-CoV-2 is just the latest chapterin a long story of viruses jumping from oneanimal species and into our own: What we call“zoonotic infections”

And when we take a moment to understand why,when, and how that happens, it can teach ussome really important lessons about how toavoid SARS-CoV-3 or whatever the next oneis… because if we don’t change anything,experts are 100% certain this will happenagainSo, speaking of experts, I called one up:science writer David QuammenIn 2012, he wrote this book, “Spillover:Animal infections and the Next Human Pandemic”

This is a book I think about a lot, whichis why it’s on the shelf behind me in prettymuch every other video I makeDavid’s book basically saw all of this coming:A fast mutating respiratory virus that jumpedout of a mammal in Asia into Homo sapienscausing a massive global pandemicSo I asked him how he was able to make thesepredictions so many years agoWhen things get really bad and people startgetting sick around the world, everyone seems

To call youMy book contains pretty precise predictionsof what is happening now, not because I wasprescient, but because I was listening toa carefully selected group of disease scientistsand public health peopleWhen I published it back in 2012, a lot ofpeople said, “Oh, that’s quaint: animalinfections and the next human pandemic

That must be this sort of fringe subject outon the edge of medicineThat was the reaction then, except among acertain number of people who said “yeah,that’s what’s going to happen”And just like experts predicted, it did happenSARS-CoV-2 jumped out of another species,most likely a bat, maybe passing through anotherspecies in between, and into humans, causinga global pandemic that has infected millions

And killed hundreds of thousands in just monthsZoonotic diseases are definitely no longera fringe subject on the edge of medicineSo now that the world is paying attention,we’re going to take a look at why and howthese things even happenAnd it turns out they are not newAs variously estimated, scientists say 60to 70% of human infectious diseases are zoonotic

Diseases – coming from non-human animals,spilling into humansI was completely shocked when I heard thatnumberMost human infectious diseases originallycame from other animals60 to 70% of them!Scientists today know that from comparinggenetic sequences from germs taken from wildspecies with germs that infect us

And they see similarities to tell us manyhuman germs are the distant offspring of thosethat we find in wild speciesThey somehow made the leap into usI have a chapter in Spillover titled “everythingcomes from somewhere”And when you think about it, we’re a relativelyyoung species, they reckon 200,000 yearsSo we’re here, and we have infectious diseases

Where could those infectious diseases comefrom, except from other animals?Think about thatBubonic plague or COVID-19, every diseasethat we get had to come from somewhereAnd even for germs that have called us homefor millennia, that “somewhere” is mostlikely other animalsMeasles is considered an only human disease

It comes from some sort of a wild morbililvirusand diverged from an animal virus maybe 4thcentury BCOther estimates maybe say 9th century ADOur smallpox was a divergent strain that hadgotten into humans from animals, a long, longtime ago, tens of thousands of years agoMaybe what we now call a cowpox, or a horsepox

Then it stayed in humans long enough, andit was evolving fairly quicklySo it diverged and became uniquely a humanvirusNow, smallpox is special for another reason:It happens to be the only infectious diseasewe’ve ever completely eradicatedAnd that was only possible because the smallpoxvirus that infects humans isn’t out therehiding in another animal species, waitingto jump into humans again

And that brings us to the first ingredienta germ needs in order to make a species jump:A reservoir hostAnimals in the wild are constantly gettinginfected with viruses, but those animals don’talways get sickBecause if a virus is too successful, it justruns out of hostsSo instead, sometimes it just quietly hangsout inside a reservoir species

This is one reason there’s such an unfathomablenumber of viruses out there, enough to stretchacross our galaxy and beyondAnd those viruses are constantly encounteringnew hosts and trying to infect themBut these attempts almost always fail, becausethe two hosts are just too differentFor a virus that’s adapted to infectingfish, the human respiratory tract might aswell be another planet

But!When viruses reproduce, they do it by themillions or billionsSo they can develop a lot of mutations reallyfastMany of these mutations don't do anything,and many actually make the virus worse, butevery once in a while a virus randomly rollsthe mutation dice and wins the jackpot: theability to infect a new host

That virus opens up a whole new universe whereit can make more of itself, and in the gameof evolution, that's the only prize that mattersAnd if I – the virus – can do that, I’mon my way to a new phase of evolutionary success,a more ambitious phase than what I had whenI was living in low concentrations in my reservoirhostI was keeping it on the down low, I wasn’tmaking a lot of trouble

But the evolutionary mandates: replicate yourselfas much as possible, as quickly as possible,and extend yourself in space and timeThen you perpetuate yourselfThat’s the survival of the fittestThat’s what viruses as well as people, anddandelions, and rats doAnd the closer two hosts are on the evolutionarytree, the fewer mutations a germ needs to

Let it make that leapA virus adapted to a close relative of ours,say chimpanzees, might not need many mutationsat allScientists now think HIV made a leap justlike this, from chimpanzees into humans, sometimeearly in the 20th century, when a human huntedor came in contact with blood from an infectedchimp

And this brings us to the next ingredientfor a spillover: ContactThe churning and cooking of evolution is alwayshappening everywhere, in every organism, everyecosystemWild animals, they're trading viruses allthe timeIt’s not just wild animals, nonhuman animals,sending their viruses to us, downloading theirviruses onto us, dumping on us

Viruses are moving every which way, all thetimeBecause all wild animals carry viruses, theycarry a diversity of virusesBats, for instance, carry a lot of virusesincluding a great diversity of coronavirusesIt’s important to say, these viruses don’twant to spillover from bats or rodents intohumansThey’re not after us

We simply present ourselves as an incredibleopportunity to themEven now, there could be a virus, hiding outin tigers in Siberia that could infect rabbitsin AustraliaThe thing is, those species will never comeinto contactThing is, the human species is in more places,interacting with more wild stuff than anyother species on Earth, when we destroy thosewild places, or bring wild things close to

UsThe wording that people use is that an animalhas “caused” a disease in usI'm sensing that doesn’t really line upwith how these spillovers are happeningThere’s nothing special about us, there’sjust more of usWe’re the world’s biggest target for viruses,but we’re not the only targetEvery time we come in contact with a wildanimal, we offer ourselves as an opportunity

For new possibilities, a new hostAnd as I said, the virus doesn’t jump intous, it doesn’t look at us and say wow that’sa great opportunityThe virus falls into us, we bring the virusinto our cellsBy bringing these wild animals closer to usBut even if all these ingredients are there:a virus mutates in a reservoir host, it wins

The virus lottery and comes into contact withone human, and it’s able to make the leapof infection into one person, well, that’sstill not enoughTo spread, a germ needs to be able to transmitbetween peopleBecause two new hosts means double the chanceto mutate and evolve into an even more successfulvirus, and so on, and so onIf someone was going to design the perfectbioweapon, they might build an aerial vehicle

That you could fill with infection, and thenget to every major city in the world withinhours, where those containers would be openedup and that infection would be dispersed intounsuspecting crowdsIn other words, you’d invent air travelNow, I’m not saying airplanes are badIt’s totally amazing that we’re intelligentenough to build flying machines that can connect

Every corner of the planetBut I’m using it as an example of how thetools that connect us also connect our germsIt’s an irony that we humans are closelyconnected, that’s both an advantage anda disadvantageWe need to be closely connected because weneed scientific information to be passingat the speed of light around the world sowe can be prepared for the next one

But the downside is, there are these drone-likemachines that carry viruses all over the worldand drop them into citiesWe are the final ingredient of a zoonoticpandemicThe human species is reaching into the wildeverywhere we can, and pulling out germsWe're pouring fuel on the fire of virus evolutionThere’s SARS CoV-3 and SARS Co-V-4 out there So yes, we have to change our behavior or

There will be more versions of this spillingover into humans, causing outbreaks, if notcausing pandemicsDoes this give us an opportunity to becomeaware of our place in nature in a differentway?Absolutely We have a tendency to think ofourselves as separate from the natural worldThere’s humans, and the human world

And then there’s the natural world overthere – maybe you go there on Sunday to takea hikeBut there is no this world and that world,there’s just the worldOne of the scary things that Darwin said tothe world in 1859 was that we humans are animalsWhat’s a really good reminder of that?We share diseases with animals

A virus that infects a bat can infect us tooIt happens because we’re mammals like themAnimal disease, human disease, same diseaseThere’s something that David wrote that’sstuck with meHe wrote this about Ebola, another zoonoticdisease, while he was hiking through the junglesof Central Africa a few miles from an outbreak,but it applies here, and it applies to our

Future: “the virus is not in your habitatYou are in its”I knew that Ebola was there, it was everywhereand nowhereEbola is not everywhere on the planet rightnow, but this novel coronavirus isIt’s here, it’s among usWe’re in its habitat

And it’s time to think like thatWe are its habitatStay curiousFinally I just want to say a huge thank youto everyone who supports the show on PatreonLike so many other people, COVID-19 has completelychanged the way that we workBut I just feel very very lucky that we arestill able to bring you these videos and hang

Out together and learn something along thewayAnd that is thanks to your supportIf you'd like to join our community, there'sa link down in the description where you canlearn more and all the great other stuffAnd if not, just happy that you're here watchingthis videoSee you next time

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