Are We Safe From the Real World Parasite that Inspired The Last Of Us?

Thứ sáu - 17/05/2024 22:39
From the Salem Witch trials to organ transplants, a leading disease expert reveals the shocking historical truth of this very real fungus.
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When it comes to horror, there’s nothing more terrifying than the plausible. As much as we love cowering from supernatural scares, when we leave the cinema, we do so knowing that vampires aren’t really going to hurt us. That a vengeful spirit probably isn’t lurking behind the counter at our local Starbucks. 

For decades, thanks to beloved films like The Thing and Shivers, the idea of a virus or foreign body enslaving mankind fell into the same comfortingly fictional category. Yet, with post-apocalyptic PS3 classic, The Last Of Us, it turns out the game’s gruesome premise is far closer to reality than most think. Created by developers Naughty Dog, this fun(gal) take on the age-old zombie yarn is set in a future where 60 percent of humanity is wiped out by a parasitic fungus – the Cordyceps.

The chilling part? This skull-bursting fungus actually exists. And now that The Last of Us has been adapted into a beloved and acclaimed TV show, audiences of even greater numbers have been exposed to the terrifying prospect of a fungal takeover. To be well-informed is to be well-equipped should the worst-case scenario happen — so we urge you all to read this. You can thank us later.

At that time in the early 2000s, [the cordyceps] was very much ignored. People really didn’t imagine parasites could do such complex things…

After years of evolution, little-known parasite, the Cordyceps, has slowly spread across South America, using its spores to infect and manipulate helpless ants, beetles — and even spiders – leading them all towards grizzly, painful deaths. In other words, the true tale of the Ophiocordyceps was begging to be adapted into a full-blown zombie nail-biter. So much so that around the same time as the game’s release, MR Carey’s novel The Girl with All the Gifts came out. Based on his earlier short story, the book has a similar premise revolving around the same fungus, and was followed in 2016 by a film adaptation starring Gemma Arterton and Paddy Considine.

Yet as brilliantly horrific as the colourful clickers and spore-ridden stalkers of The Last Of Us are, with only insects affected in reality so far, is our species really at risk from this remarkably tenacious little fungus?

We spoke to renowned disease biologist and Penn State University’s professor of Entomology and Biology, David Hughes, in order to find out.

Believing the unbelievable

“I came to [the Cordyceps] through Richard Dawkins who was on my PhD committee, and through another extraordinarily famous scientist called Bill Hamilton, who was my supervisor,” Hughes explains.

“At that time in the early 2000s, [the Cordyceps] was very much ignored. There were just these examples, anecdotal observations and [they were] oftentimes discredited. People really didn’t imagine parasites could do such complex things…”

It was this complexity that fascinated Hughes. Rather than just spreading through infectious spores and paralyzing its host like most parasites, once the Ophiocordyceps spores find their way inside an ant, chillingly, the fungus begins to manipulate its prey. Disorientating it, the organism turns the ant into an unwilling marionette, rotting its insides while controlling its limbs, forcing the ant to march toward a leaf and bite into it. Once happy with its chosen spot, in brutal fashion, a tendril then erupts from its victim’s head, launching its spores onto any other ants unlucky enough to be nearby.

Sound familiar, Last Of Us fans? Thankfully for us though, the Cordyceps’ gruesome nature makes it surprisingly easy to trace.

“I went to work in Mexico and Costa Rica [to witness them in action],” says Hughes. “Every time you find a dead ant in the forest biting onto a leaf, the parasite is still alive…. So essentially, you have a frozen record of what happened. It’s like the behaviour of being fossilised. You can go to a forest and you’ll find hundreds of them in a small area … little calling cards which tell you exactly what happened with the manipulated behaviour in the [ant’s] last moments.”

Taking the ‘fun’ out of fungi

It’s a good thing that someone was paying attention. Hughes explains that the Cordyceps has actually been quietly infecting our forests for millions of years, but it wasn’t until 2008’s season of BBC’s Planet Earth that most of the world’s populace had even heard its name. Naughty Dog’s Neil Druckmann was among them. Midway through the development of Uncharted 2, Druckmann turned on the TV and witnessed this harrowing real-world zombification play out right before his eyes.

1.3 million people die every year because of fungal diseases…there’s no reason we can’t get these diseases.

While Hughes claims there was actually some manipulation going on in the Planet Earth episode (“When you look at the video, Attenborough says the ants detect the infected individual and throw it out of the nest and carry it off — and then you see it cleaning itself. This is all made-up nonsense. The BBC sprayed that ant with hairspray in order to get it to have that cleaning behaviour. ”) Yikes. Nevertheless, what Druckman saw on Planet Earth inspired him to use the cordyceps as the basis for a new, truly plausible zombie game.

A few years later, he’d approach Hughes to be Naughty Dog’s adviser on The Last Of Us.

“People get fungal diseases all the time,” explains Hughes, when asked about the possibility of a Cordyceps-induced apocalypse. “If you’re immunocompromised, a fungus is most likely what’s going to kill you, especially say, if you’ve got AIDS. In fact, fungi kill more people than malaria — 1.3 million people die every year because of fungal diseases. So, there’s no reason why we can’t get these diseases.”

He pauses, “The question would be: if we did get an Ophiocordyceps-contracted disease, would it be able to control our behaviours?”

It’s a good question, and we’ll be honest – we really hope not. Comfortingly, so far, mankind hasn’t really encountered a virus or parasite that can completely control it. While rabies may be able to send us into fits of murderous rage (and shockingly, kill 50,000 people a year) it doesn’t quite fit the zombification profile. The Cordyceps being able to confuse and sedate insects is one thing, but there’s no way its genus could ever evolve to a point that it could actually manipulate human beings… right?

The historic horror of the cordyceps

“Well, it already has compounds in it that have historically affected human behaviour. Ergot is a fungus that lives inside grasses and that is evolved from the worms and the ants, and it produces alkaloids that control behaviour. In Europe, there was something called St. Anthony’s Fire, which is these convulsive deliriums that have been going on for thousands of years, as people ate infected rye. There’s even a strong suggestion that the madness of the Salem Witch trials in the 1600s was due to people eating infected rye which contained this fungus,” says Hughes.

So much for The Last Of Us being fiction. If that wasn’t terrifying enough, it turns out, it’s not just rumoured hallucinogen-induced madness that the Cordyceps causes – the parasite has been directly linked to inciting bloodthirsty rage in humans.

“The last case was in 1954, thereabouts, in France when somebody intentionally sold a load of grain to a small French town containing the fungus. Everybody went mad and some 12-year-old girl tried to kill her mother with a kitchen knife,” Hughes explains. “So, yes, consuming the fungus will drive you crazy, and getting infected is possible. But it jumping from ants to humans and then onward [to other people] … that probably requires too many [improbable] circumstances to happen.”

The madness of the Salem Witch trials in the 1600s was due to people eating rye which contained this fungus.

Before you start committing ant genocide though, as the vast majority of the planet chooses not to eat insects, Hughes concludes that it’s quite unlikely that the parasite would encounter us frequently enough to be able to adapt to our digestive system.

“70% of diseases come from animals that we either lived with in the past or that we eat, “ he explains, “We get diseases from pigs and poultry because that’s what we consume and spend a lot of time in close quarters with.”

Welcoming parasites with open chests

Yet there is one way we already willingly(!) let Cordyceps inside our bodies – through organ transplants. We’re no experts, but, with parts of this fungus regularly being used to help stop patients from rejecting their replacement organs, this sounds like a shockingly easy way for us to accidentally trigger a real-world zombie apocalypse. In fact, this is exactly what caused the zombie outbreak in the original novel World War Z by James Brooks….

So, why are they used then? Well, cleverly, our bodies naturally repel foreign organs. Always on the prowl for invading germs and other foreign organisms, it’s no surprise that we’re built to reject new organs – yet after the new organ has been injected with a byproduct of the Cordyceps, it’s then welcomed with open arms. While less common in the West, this cordyceps byproduct is still regularly used to assist with organ transplants in China. We don’t know about you, but we’re suddenly rather terrified…

“[Using Cordyceps to assist with organ transplants] goes back to the 1950s,” Hughes explains. “There are some variations of the Cordyceps which can help improve your immune system and there are others which tamper it down. So, if you’re getting an organ transplant, you’re going to be treated with a product of this fungus, either something that has been made in a lab or something that is just generated in a big vat somewhere.”

With Hughes serving as the resident disease expert on the film adaptation of World War Z, he’s no stranger to the idea of organ transplants being a gateway to Cordyceps’ human takeover. Yet, while this all sounds worryingly plausible, given the current ways the Cordyceps is used in organ transplantation, he insists that if done correctly, the phenomenon would be near impossible.

World War Z is unlikely to become reality… accidentally, anyway

“Thankfully, the drug itself is isolated,” Hughes explains, “What we currently do is just grow the fungus in a jar somewhere, take out the compound and inject you with that compound. But if we were using the active organism during drug therapy, then you can imagine how there could be a jump [to a new species].

“….So, if, for example, every time you got a new kidney or something they put an inoculum of the fungus into that area of your body and that replicated, then you can imagine how that would be able to stay within the host and have onward transmission.”

“The biggest barrier [for the Ophiocordceyps taking us over] is our body temperature,” he continues, “and that generally holds fungi at bay unless you’re immunosuppressed — with AIDS for example. So, it would have to be able to cope with that.”

Before you go and treat yourself to a new kidney and tuck into a bowl of infected rye though, Hughes suggests that there’s still one way in which the Cordyceps could plausibly make the jump to our species — after a natural disaster.

Cordyceps: are ants really the last of them?

“It’s really difficult to control viral infections in a densely populated area. Measles, for example, or smallpox… but in most cases, fungi don’t seem to transmit that well. So, you’d want to find conditions where it could manage to get better transmission…

“After the hurricane in New Orleans, for example, where it was flooded there were a lot of fungal infections and contaminants afterwards, because of the conditions of mould. Another fungus called valley fever tends to transmit very well in prisons — because you have crowded conditions and it tends to be damp. It even differentially affects different races. So, there might be a way in which certain people are more likely to be infected than others.”

“In other words, there’re a few barriers for the Cordyceps to overcome. But given our crowded living conditions and given our accelerating poverty, there might be conditions where we’d promote more fungal transmission rather than less.”

If there was some way we exposed ourselves to the infected insects more often, that’s a mechanism [for the cordyceps to spread]

Oh god, the fear’s back again. Still, even if humans live in close quarters with each other in hugely damp and squalid conditions, there’s still the matter of the Cordyceps having to make an improbable evolutionary jump. And as Hughes mentioned earlier, it’s incredibly rare for a disease to jump from insects to animals. So we’re probably fine, because that just can’t happen…. right, Hughesy?

“Well, there was of course the Black Death..”

Oh, for f–– sake.

The next step

“The Black Death wiped out one-third of Europe,” he continues, “That was transmitted from an insect into a rat and then eventually from a rat into humans. So, if there was an intermediate infection and some way we exposed ourselves to the infected insects more often, that’s a mechanism [for the Cordyceps to spread]…”

We’re almost scared to ask this question, but… while the Ophiocordyceps has only achieved this nightmarish level of manipulation with ants in South America, what about the risk posed by the millions of potential carriers currently marching beneath our feet?

“There are, of course, enormous numbers of ants in cities, but those species of ants have not yet been infected by the Cordyceps. There’s one [ant species] called a pharaoh ant, because it’s been associated with human habitation since Egyptian times. Back in the ‘70s, this was a big problem in London where they would get into radiology wards and into the dressings of patients, tracking all the infected material all over the hospital or the radioactive material. You could use a Geiger counter and actually see the tracks of the ants through the hospital wards….”

“In other words, they’re pretty impossible to get rid of and you can imagine a situation where we’re now getting exposed to them more often. So [for us to get infected] there either could theoretically be an intermediary — a mammal that gets close to the ants and then us, like the Black Death — or just a greater occurrence between ants directly and us.”

One unlikely factor may have saved our species so far: our multicultural communities

Before speaking to Professor Hughes, we assumed that there was almost no chance of us ever coming face to face with a clicker. That The Last Of Us was an intruiging but totally far fetched bit of virtual fun. Now, however, it seems the fungal-induced zombie apocalypse is just highly unlikely, rather than completely impossible.

Before you start stocking up on rations and manically setting fire to wild mushrooms though, it’s comforting to know that the rather large evolutionary jump the funghi would have to make renders the Cordyceps zombie all rather improbable. In fact, Hughes suggests one unlikely factor may have saved our species so far: our multicultural communities:

“Ant societies are this collective where all of the ants in a nest are female and they share 75% of their genes. So, it’s like a highly inbred society living in massive density in a dirt-filled environment (the soil) … the conditions are ripe for the spread of diseases. So, in order for ant societies to be successful, they need to have what’s called social immunity, which is recognising infections in the nest and eradicating them.”

While a more simplistic spore was enough to fool more solitary insects, the society-based ants could easily warn their colony and move on, meaning that the poor old Cordyceps had no choice but to adapt into something that could mimic the ant’s behaviour — just enough to fool the colony. And thanks to their closely shared genes, this fungi found a way.

“So, we determined that the Ophiocrydceps’ ancestor was in a beetle larvae living in rotten wood. And it likely jumped from the beetle larvae into an ant colony, which are very common in rotten wood. But immediately upon jumping there was strong selection on the fungus to evolve manipulation that [makes the ant] go outside of the nest, otherwise, the strong social immunity of the ant colony would be an evolutionary dead-end for this fungus.”

Thanks to our overall genetic diversity as a species, it’d be incredibly difficult for the Cordyceps to be able to adapt enough into something that could successfully manipulate different races equally. But that doesn’t mean that, given extreme overcrowding, it couldn’t infect humans with or without basic manipulation… eventually.

Are we safe from the Ophiocordyceps then? For now at least, yes. Yet, thanks to the rapid rise in the Earth’s temperature, increasingly overcrowded cities, and aeroplanes allowing us to spread horrible diseases across the globe in a matter of hours, it’s not hard to see how a virus like this could easily spread.

Maybe just forgo that vanity organ transplant you were eyeing up, just in case….

This is an updated version of an article first published August 29, 2019.

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