The science behind the ‘zombie fungus’ in ‘The Last Of Us’ — and why it (probably) can’t happen

On Sunday it was time for another episode of the hit HBO series “The Last Of Us.”

In this take on the zombie apocalypse, we see a post-pandemic world that’s been taken over by zombies. But these are not the typical zombies we’re used to seeing in movies and TV shows like “The Walking Dead,” these zombies have been infected by fungus that invades the bodies of its hosts and takes over their minds. 

The popular TV show, which was originally a video game, may seem like science fiction, but the fungus in the show is based on science fact. 

The show highlights a particular type of fungus called “cordyceps.”

There are thousands of species of cordyceps, and most are specifically designed to infect a particular species — typically insects — turning its victims into a zombie. 

One of cordyceps favorite victims are ants. That’s because as insects, their bodies are quite rudimentary compared to mammals and the fungus has evolved over millions of years to become the perfect body snatchers. 

In ants, cordyceps slowly infects its victims to help it complete its life cycle. The all-consuming fungus must zombify ants in order to live.

That’s because it needs certain environmental conditions to thrive and by mind-controlling its host, the fungus is able to get the ant to transport it to a humid climate where the conditions are perfect for its growth. 

The fungus then slowly consumes the ant, replacing the ant’s cells with its own, until there’s nothing left but the exoskeleton. Once the fungus has completely taken over, it releases spores to trap other victims. And this is typically near the ant’s own colony so its spores will have more victims to keep the cycle going. 

Ants aren’t cordyceps only targets, certain types of fungus infect different insects, including tarantulas. In this scenario, the fungus spores burrow into the spider, spreading its wispy tendrils — known as mycelium — throughout the spider’s body.

Once the spider’s insides have been replaced completely, the fungus bursts through its body and produces spores so the cycle can begin again. 

We see characteristics from different types of cordyceps in the show, and lucky for us, humans are not one of cordyceps’ targets.

According to scientists, there are approximately 150,000 known species of fungi, and only about 200 are known to infect humans. Experts also say that an estimated 1.7 million deaths each year are caused by fungal infections, with many more severe cases. 

That’s because as humans, we have an incredibly advanced immune system to help protect us and a much higher body temperature than the cordyceps prefer. 

So, fungi are infectious, but not in the same way that’s presented in the show. While they won’t turn a human into a mindless zombie, they can still cause damage. It’s estimated that roughly a billion people each year have some sort of skin, nail or hair infection each year that’s caused by fungus. 

Patients with underlying and chronic health conditions can develop more serious fungal infections and according to a report released in 2022 by the World Health Organization, there are 19 fungal pathogens that pose a threat to humans.

Luckily for us, the zombie-fungus is not on the list. 

Could a fungus ever cause a global pandemic?

That idea is pretty far-fetched, according to Tom Chiller, chief of the Mycotic Diseases Branch at the Centers for Disease Control and Prevention.

Chiller says that while some species can spread from person to person, they don’t spread in the same way that viruses, like COVID-19, do. That’s because most viruses spread through respiratory droplets, whereas many fungal infections need skin-to-skin contact.

This makes it highly unlikely that a single fungus could spur the same kind of global pandemic we see with viruses. Fungi are also more self-sustaining than viruses, which need to infect a host to live. 

Global pandemics can become increasingly likely.

As the space between humans and the natural world continues to get smaller and smaller, the chances for pandemics increases.

It allows pathogens to make the jump from animals to humans more easily and we could see the emergence of diseases like the Sars virus that is responsible for the COVID-19 outbreak. 

“I know that we’re going to see more of these fungi move into humans and into animals,” he told the Hill. “We need to be constantly doing surveillance to understand how these things emerge.”

We also need to be more aware of how a changing climate affects global health. Just like in “The Last of Us,” researchers have found that certain types of fungus can adapt to rising temperatures, which could also mean that the more pathogenic fungi could also do the same.

But Chiller says the big things we should be focusing on are better ways of diagnosing fungal infections in the field and more research needs to be done to improve and develop new treatments.  

“We really only have three classes of drugs to treat severe fungal infections,” he said. “But what if a particular strain is resistant to all three? We do have drugs in development, but we need a lot more.”

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