THE REAL ZOMBIES BEHIND “THE LAST OF US”

The Last of Us, an award-winning fungal zombie apocalypse TV show currently taking the small screen by storm, is lining up for a second anticipated series. Thankfully though, all that zombie nonsense is pure science fiction and couldn’t happen in real life… right? 

The Last of Us TV show (or TLOU) is actually based on a popular video game series. Both follow the story of survivors Joel and Ellie as they travel across a world devastated by a fungal plague that turns its infected hosts into horrific mycological monsters in an attempt to find a cure. The fungus in question is the parasitic Ophiocordyceps unilateralis – or cordyceps – and it actually exists in real life.

Moreover, the fact that it makes zombies is just as real.  They’re not the same monsters of the TLOU franchise, but that doesn’t make them much less horrifying. You see, cordyceps is also known as zombie-ant fungus, and it does turn its hosts into unwilling puppets. Ants that encounter spores in their rainforest environments will find themselves vessels for a fungal colony that infiltrates the insects’ exoskeleton and forcefully overtakes their nervous systems. 

But the real question is, why? As with the TV series, the cordyceps’ modus operandi is to spread. The fungus leaves the ant’s brain intact and takes direct control of the muscles, piloting its host away from its colony and high into the trees where its jaws clamp onto a leaf and atrophy. Cordyceps is then free to devour its “vehicle” and shoot out a growth from the ant’s head to spread more spores and repeat its propagation. 

They all sound like something out of a horror movie, but they’re happening every day out in nature. However, unlike in The Last of Us, they pose little threat to humans. In the show it’s suggested the infection made the jump to humans via a common food source, but Scott Roberts, MD, who works as Yale School of Medicine’s assistant professor of medicine (infectious diseases), says that can’t happen. 

“There are millions of different fungal and mold species out in nature that don’t cause any sort of infection in humans, and this is one of them,” Dr. Roberts told Yale School of Medicine in 2023. “A Cordyceps that infects one species of ant cannot even infect other species of ants.” 

Although their processes are enigmatic, experts are getting closer to understanding how they work by observing other behaviour-manipulating parasites. Toxoplasma gondii – a parasite that belongs to a group called alveolates – has been a significant source of study in that regard. It targets rodents, and the results of its behaviour are troubling, to say the least! 

It appears that the parasite somehow alters anxiety levels in rodents such as mice and cats to bypass their learned fear of the scent of cat urine. And when they don’t fear the smell of their biggest predator, they’re more in danger of getting eaten which, in turn, passes the parasite into the cat’s stomach where it can breed even more of its kind. 

While this is all a little disturbing, it gets worse: Toxoplasma gondii can also infect other warm-blooded creatures too, with similar results. And if you don’t believe that’s much of an issue, tell that to chimpanzees.

A 2016 study observing chimps discovered that while the scent of leopard urine repelled non-infected apes, the ones with the parasite remained unphased. Interestingly, this was only the case with leopard urine – the native predator of the chimps – and not the urine of tigers or lions, which the apes were unlikely to encounter in their natural environment. 

Not scary enough? Well, T.Gondii can also affect humans – using us as an intermediate host between cats and rodents – and studies suggest it affects our behaviour, too! Research conducted via ScienceDirect in 2020 claims that humans infected show a higher frequency of personality disorders, including suicide attempts, schizophrenia and incidents of road rage. 

It isn’t just linked to negative attitude changes, though. Apparently, T. Gondii has been associated with success in business! It would seem that entrepreneurs affected by it show reduced levels of fear and are therefore more likely to take risks on new businesses and similar endeavours.

The real thought-provoking thing is that nearly a third of the human race is affected by T. Gondii already, but thankfully most healthy adults seem to be asymptomatic, so as far as we know, there’s little to be concerned about. So while a zombie plague similar to the one in The Last of Us is unlikely, climate change has increased the spread of fungal diseases. Dr. Roberts reported, “What does concern me as an infectious disease physician is a relatively new fungus called Candida auris. This fungus spreads person-to-person, which hasn’t really been reported before.” However, The Last of Us might actually help in that regard. “The show might not be realistic,” Dr. Roberts explained, “but pathogens like Candida auris are likely going to get more press now. That’s only going to help us out.”