In the video game and HBO show The Last of Us, humans struggle to survive after an infectious fungus turns ordinary people into zombies. Creators of the franchise didn't look far for inspiration — the series is based off a real-life species of fungus that performs a kind of "mind control" on its insect hosts.
Ophiocordyceps unilateralis, otherwise known as cordyceps or zombie-ant fungus, infects insects such as ants or spiders. Like other parasites, cordyceps drains its host completely of nutrients before filling its body with spores that will let the fungus reproduce. It then compels the insect to seek height and remain there before it expels these spores, infecting other nearby insects in the process.
Bryn Dentinger, a biology professor at the University of Utah and curator of mycology at the Natural History Museum of Utah, told NPR that the fungus is one of the best known, and probably most commonly encountered, kinds of organisms with this mind control capability.
And he said that scientists aren't entirely sure how cordyceps is able to have the effect that it does on insects, although there are theories.
"There seems to be some combination of physical manipulation of muscle fibers, for example, possibly growth into the brain itself, that can impact its behavior," he said. "But there's also very likely some sort of chemical attack on the host, either small molecules, or proteins or some other things, that end up manipulating brain behavior."
Dentinger, who is also a fan of HBO's adaptation of The Last of Us, said that there are some major differences between how the fungus is portrayed in the show and in real life. Cordyceps does not typically infect other hosts through the mouth, for example, and the infected aren't connected to one another through a network.
And, perhaps the most important: The fungus cannot infect humans.
"Our body temperatures are high enough that most organisms, their proteins would denature at that temperature and so they can't survive in our bodies," he said.
But there are species of fungus that are able to withstand higher temperatures, and can therefore infect humans. Climate change, as Dentinger explains, is equipping certain fungi with the capacity to withstand higher temperatures.
And it's possible that a fungus with similar mind-control capabilities could, at some point, be able to withstand a human's body temperature.
"That may be one reason why we're seeing more fungal infections in human humans, but again, to date, none of them are cordyceps," he said. "However, maybe that will happen in the future, but, at the moment, that is not a possibility."
And, as Dentinger, there are already species of fungus that alter a human's mental processing, such as psilocybin, otherwise known as "magic mushrooms."Meanwhile, other kinds of fungi are already ubiquitous in human life. Take yeast, for example, which is found in bread and in the human gut.
And while the prospect of fungus being able to manipulate human behavior isn't impossible, it's not likely, according to Dentinger. The traits the fungus have that allow them to attack an insect host are very specific to that insect — and it's not easily transferable to another species.
"It's unlikely that they would be able to hop from, say, an ant to a human, because we're so different," he said.
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