In what can be described as a lightning-strikes-twice scenario, both “The Last of Us” video game and the TV show it inspired are both hits. Unsurprisingly, the events detailed in the show and the game have given rise to some questions: Could a zombie fungus pandemic be in our future?
Here’s a look at how the cordyceps fungus works, how it stacks up against other infection vectors, such as bacteria and viruses, and if “The Last of Us” might come for us next.
Don’t Bug Me, Man
Let’s get this out of the way first: There is absolutely a type of zombie fungus — ophiocordyceps, often just called cordyceps — that can infect insects, such as carpenter ants, caterpillars, spiders and dragonflies.
Once inside the insect, cordyceps creates and releases chemical compounds that force the insect to change its behavior. The purpose of which is to spread more fungus. Cordyceps accomplishes this goal by compelling infected insects to climb or fly to high places and then bite down on a branch or leaf. Next, their jaws lock, and they remain in place until the fungal growth cycle is complete, which is when spore stalks burst out of the insects’ heads and bodies.
Gruesome? Undeniably. Effective? Absolutely.
Since the fungus forces the insects to climb, the spores released can travel farther, in turn infecting more insects to start the cycle anew.
He’s Not a Fungi
With recent pandemic experiences fresh in our minds, there’s a worry that these fungi could make an evolutionary leap and start taking the fight to humans. But how do they stack up against bacteria and viruses when it comes to infecting larger mammals?
As a recent CNET piece points out, not great: Where bacteria and viruses have adapted to infect human systems and fight back against immune responses, fungal attacks aren’t well-suited to our warm-blooded bodies. It makes sense, as most instances of cordyceps infections are seen in hot, wet climates where the fungus can flourish outside of hosts. Inside infected insects, meanwhile, simple organ structures and the inability to regulate their own body temperature make them the ideal hosts for fungal homes.
This isn’t to say we’re immune to diseases caused by fungi or illnesses that can change our behavior. For example, Candida auris is a yeast that causes thrush and is a concern in places like hospitals, where most humans have compromised immune systems. What’s more, this fungus is drug-resistant, making it harder to treat once it manages to infect someone. There are also more common and less serious fungal concerns, such as the strains that cause athletes’ foot and ringworm. What they have in common is that, once they take root, they’re difficult to remove.
There’s also precedent for infections changing human behavior. For example, if left untreated, the rabies virus can cause those infected to become aggressive, delirious and afraid of water. While there’s no impetus to climb large trees and spread viral particles, rabies nonetheless alters behavior via infection.
Global Warming, Fungal Warning
When fungi make their way to the U.S. in “The Last of Us,” it takes only a few days for society to collapse. In large part, the quick decline is tied to fungal spores in common foodstuffs — with massive numbers of people infected and the incubation period taking only a few days, society finds itself thrown into sudden chaos as fungal freeloaders take over.
Global warming is linked to the ability of cordyceps to thrive and survive in new climates. In the HBO show, worries around global warming are discussed — but ignored — years before the infection. As noted by CNN, however, while increasing temperatures could make fungal infections more common, it’s unlikely they would trigger a pandemic. Those with weakened immune systems might be at greater risk, and effectively targeting diseases caused by fungi is more challenging given that they share the same basic cell structure as humans, but even a warmer world shouldn’t trigger a global disaster.
“The Last of Us” Disease: Our Fungal Future, or Frightening Fiction?
In “The Last of Us,” one of the worst parts of the infection is that the infected know exactly what they’re doing — they just can’t stop themselves. Some scenes show first-stage infected, known as “runners,” crying or screaming as they bite other humans. This mimics the effect of cordyceps in nature; insects are aware of what’s happening (as much as any insect can be), but they’re powerless to stop it. Given the depth of emotion made possible by human brains, this loss of control would be terrifying.
But is this our fungal future?
Probably not. As noted, humans aren’t great hosts for fungi. While some strains do infect us, others are used to combat infection and improve our overall health. And while global warming does pose a potential problem if cordyceps and other strains manage to survive in different climates, we’ll likely have bigger issues to worry about at that point.
In addition, Scientific American notes that there are strains of cordyceps that are beneficial to humans. Sometimes called “Himalayan Gold,” cordyceps sinensis has been used for centuries to treat headaches, coughs, liver disease and kidney disease. This type of fungus infects and kills caterpillars — instead of forcing them to climb, however, it forces them to stay underground with just their head above the soil. It then kills the insect and grows out of its corpse.
So, yes, you read that correctly — humans are already ingesting a form of cordyceps for its beneficial medical properties, and while the jury’s out on how effectively this fungus fights specific illnesses, it hasn’t caused a parasitic pandemic just yet.
The disease from “The Last of Us” is based on a terrifying, absolutely real concept that makes for great television and video games. Chances are, however, that it’s one of the last things humans should be worried about — we’ve got enough on our plates already.
Are you interested in science and innovation? We are, too. Learn more about our people and life at Northrop Grumman, or check out our career opportunities to see how you can be a part of defining possible.