In the new HBO show based on a video game of the same name, “The Last Of Us,” explores a zombie apocalypse. But these aren’t regular zombies. This feisty Sunday-night installation stars Pedro Pascal and Bella Ramsey and their experience with fungi zombies.
The show bases its fungal zombie infections on a real-life fungus. Cordyceps, or Ophiocordyceps unilateralis, is often referred to as the “zombie-ant fungus” because it primarily takes over ants and other insects. This fungus manipulates the behavior of the carpenter ant. In the show, the fungus has taken over the nervous systems of millions of humans, who are called “Infected.”
Thomas Roehl, a mycology Ph.D. student from Clark University, explained that when the cordyceps spores come into contact with the exoskeletons of ants, they get absorbed into the insect’s muscles. As the fungus spreads, it releases chemicals that command the ant to find higher ground.
Usually, the ant will climb a tree, then is “commanded” by the fungus to bite a leaf. Once it bites the leaf, the fungus kills the ant. By then, an actual mushroom has grown out of the body of the ant.
Cordyceps works similarly in the show. In the later stages of the infection, the fungus has overtaken a person’s appearance and they begin to sprout finger-like stalks out of the skin. At this stage, for the ant they are at a high elevation, so the spores it releases will be able to spread out over a larger area, Roehl explained.
In “The Last of Us” game, the spores of the mushrooms spread via spores that are released from the host human. In the show, however, the fungus spreads via the yeast and glucose in regular household items. From there, the fungus grows inside their brains and commands them to bite people.
Although the zombies in the show are not an entirely accurate portrayal of cordyceps, the creators said they drew inspiration from a few other aspects of the fungal world.
“Fungus can communicate chemically over insane distances,” said show co-creator Craig Mazin in an interview published in Screen Rant. “They are remarkable organisms, and unfortunately, in this case, also terrifying.”
In the show, if a patch of cordyceps mushrooms get stepped on or touched, the fungus will alert the Infected in the surrounding area, who then come running to that location. Although real-life cordyceps can’t directly communicate with such detail, they use a structure called the mycelium that may have inspired this tidbit from the show.
The mycelium is an underground network that extends between mushrooms of the same species. The mycelium is interconnected, so it can theoretically communicate information, according to Roehl.
Additionally, the show briefly includes the phenomenon of antibodies passing from mothers to babies. In the last episode, viewers learn why Ellie, played by Ramsey, is immune to being infected.
While in labor with Ellie, her mother gets bit by an Infected. Ellie is still attached by the umbilical cord when this happens, which is the show’s way of explaining Ellie’s immunity. But Ellie is only attached for about five minutes after the bit before the cord is cut.
In reality, it takes about two weeks for antibodies to transfer from mothers to babies, Roehl said.
“Some of these zombies [in the show] can be infected for like 15 years,” Roehl said. “So they definitely have a time where that is possible, but five minutes is false.”
Despite the fact that cordyceps choose a host to spread spores, it is highly unlikely that it will ever infect humans, João Araújo, a mycologist at the New York Botanical Gardens, said in an email.
“The fungus would need to recognize the human skin as they recognize the insect cuticle [and] adapt to overcome the human immune system, which is very different from the insect immune system and be able to sporulate from it,” Araújo said. “Each species of ‘zombie-ant fungus’ infects exclusively one species of ant, so jumping from ants to humans would be very dramatic and would require many millions of years of genetic modifications.”
According to Roehl, the fungus thrives off of a polymer that makes up the exoskeletons of the ants called chitin. The fungus is “used to” getting its food from things like chitin, and this is how it evolved to specialize in attacking ants and other insects.
“[The fungus is] not used to attacking things like keratin, like what our hair and nails are made of,” Roehl said .“So they would have to be able to find something inside us that they can eat. That’d be the hardest part for them.”
While this fungus sounds daunting, humans actually use cordyceps for many benefits. Locals to the Tibetan Plateau harvest Ophiocordyceps sinensis, or caterpillar fungus, to use for its medicinal properties. Roehl explained that people can use the fungus to make either a tea or a tincture, but they must be made while the fungus is still attached to the caterpillar.
Although cordyceps is nowhere near infecting humans, there is a prevalent fungus on the rise in society. According to Scott Roberts, assistant professor of infectious diseases at Yale School of Medicine, Candida auris, or C. auris is a yeast that has been emerging since 2009 and poses a current threat.
“We think [candida auris has emerged] due to climate change since it survives at higher temperatures. It can spread person to person, which is worrisome,” Roberts said. “It [is also] resistant to all antifungal drugs we have.”
Perhaps this fungus also inspired the zombie drama. Whether it did or not, viewers of “The Last of Us” have been hungrily awaiting season two. Although it has been confirmed by the cast and crew, its release date is still unknown.
Watch episodes 1-9 of “The Last of Us” on HBO Max today.