In zombie films that we may often watch, such as The Walking Dead, World War Z, Train to Busan, or many other films, it is told how a mysterious virus quickly turns humans into bloodthirsty monsters.
However, the currently popular HBO film series, The Last of Us, takes a different perspective on how humans can turn into vicious zombies.
In the film, the human hosts carrying the pathogen are not “undead”, in fact they are still alive. It’s not the virus that infects them either, it’s the fungus. The question many people are asking is, do mushrooms exist in real life?
This film tells the story that the deadly fungus originated in a flour warehouse in Jakarta, before infecting several people and spreading throughout the world, including to the US, the film’s setting.
The Last of Us is based on the popular game produced in 2013. Who would have thought, the creators of the game said that they were inspired by the BBC documentary series “Planet Earth”, when mushrooms take over the minds of ants. Mushroom experts, of course, don’t care how fungal pathogens can take over humans by controlling the mind.
According to Davis David Hughes, an entomologist at Penn State University, quoted from The Washington Post , this does not make sense. However, there are scientists who, while agreeing with Davis Hughes, state that there are parts of The Last of Us game and film inspired by real science.
“This is not far-fetched for me. It sounds like fiction, but to some degree, it’s true [though not in humans],” says Matthew Kasson , a mycologist at the University of West Virginia. In addition, the idea of climate change and disease that scientists are currently dealing with needs to be underlined, he added.
In the BBC documentary “Planet Earth” that inspired the game The Last of Us, the fungus Ophiocordyceps infects bullet ants. The fungus grows inside the insect, turning half of its body into a fungus. Interestingly, the ant’s brain remains intact, allowing it to manipulate the insect’s behavior.
Ophiocordyceps directs the ants to climb tree branches, where they die. Then, a fungus grows from the ant’s head, enabling it to spread the spores effectively and infect more hosts.
Thirty-five species of Ophiocordyceps are known to influence insect behavior and experts estimate that hundreds more are still missing, says João Araújo , a mycologist with the New York Botanical Garden.
There are also Ophiocordyceps and Cordyceps fungi which infect other insects such as wasps and flies, even spiders. Then there’s another group of fungi, in the order Entomophthorales , that also do manipulations—and this species looks nothing like Ophiocordyceps . Manipulation has evolved many times throughout the mushroom kingdom. The biodiversity of this fungus may be so high, scientists haven’t figured it all out yet.
How can the fungus infect the ants, and ‘take’ them over?
According to de Bekker, quoted from CNN , at first the ants took the spores [a type of mushroom seed] when they went looking for food. The spores infect the ant’s cells and a fungus begins to grow on its body.
At first, the ants might act normally. But gradually, he stopped participating in foraging efforts in his colony, and stopped communicating with his flock.
Then, these ants start to become hyperactive and no longer have the same daily rhythm as other ants. Most carpenter ants [ Camponotus ] for example, feed normally at night, but once infected they are active around the clock.
The infected ants then wander, away from the colony, looking for places in the forest to climb and bite [branches or vines]. This is where the fungus quickly eats up the ant’s body from the inside, and its host.
The fungus uses that energy to grow stalks with fruiting bodies that have spores, which fly out and infect other ants.
By climbing higher in the forest, the ants are essentially helping the fungus spread the spores. The specific site you choose can help the fungus grow. This whole process can take days or weeks, even months.
“Unlike in a zombie movie, or The Last of Us, they turn into a zombie or a monster in a matter of seconds or minutes,” said de Bekker.
However, some of the themes from The Last of Us games and films are relevant to scientists today. One is that fungal infections in humans are relatively understudied and difficult to treat. While we inhale mold spores with every breath, most of them are harmless, says de Bekker.
From 1.5 to 5 million species of fungi, humans only get sick from a few hundred of them, most of which threaten people with compromised immunity.
But more than 300 million people worldwide get serious yeast infections every year, and about 1.5 million of them die, according to a report from Wired’s Rose Eveleth , in 2021. Part of what makes these infections deadly is that they are so hard to treat. .
“Fungi are more closely related to animals than plants,” says Matthew Kasson. “It’s hard to fight them without fighting ourselves. So they had to find a special kind of compound that could kill the fungus without harming the host.”
“Humanity must put a lot more effort into studying fungi, the largest kingdom on the planet,” said Arturo Casadevall, a microbiologist at Johns Hopkins.
In the game and film The Last of Us it is also shown that what drives this planet to be taken over by fungi is the warmer temperature. Most fungi prefer lower temperatures than the human body, says de Bekker.
“It’s not a strange argument that global warming has increased the thermal tolerance of fungi,” said Ilan Schwartz, who studies invasive fungal infections at Duke University, North Carolina.
“That has not been proven. This is a hypothesis and it is happening at a fairly slow scale. … But it might happen”
The fungus Candida auris , which is resistant to some antifungal drugs and threatens people with weakened immune systems, is theorized to have adapted to human body temperatures according to a study.
But don’t panic , a widespread fungal pandemic is unlikely as the infection spreads to humans, said Dimitrios Kontoyiannis, a mycologist at the University of Texas.
Moreover, there is the fact that humans have been eating Cordyceps mushrooms for centuries now without becoming zombies. This mushroom is also an ingredient in traditional Chinese medicine, used to treat kidney and other ailments. In fact, many of the world’s medical companies market it.
De Bekker stated, everything in the human body is very different from the insects that are usually infected by this fungus, including our physiology, nervous tissue and and our body temperature. Fungi evolved developing strategies to manipulate certain insect hosts over millions of years.
“They are not generalists. Each species only knows how to handle one particular insect,” he concluded.