A parasitic fungus has ripped through the exoskeleton of an ant. (Photograph by João Araújo)
WORDS BY YESSENIA FUNES
HBO’s latest drama The Last of Us portrays a future plagued by fungi that turn humans into zombies. The Frontline explores the actual fungi that threaten public health.
Zombie enthusiasts have been glued to their televisions for the past two Sundays to watch HBO’s latest series The Last of Us. The show, an adaptation of the bestselling namesake video game, takes place in an apocalyptic world where climate change has fueled a global fungal infection that has turned most humans into flesh-eating zombies. The survivors are left navigating a highly militarized society where monsters and war run rampant.
Nowadays, we don’t have to look far to imagine a deadly infectious disease. Look at COVID-19, the virus that brought the world to a standstill in 2020 and continues to kill hundreds (if not thousands) a day. The total death toll looms over 6 million, yet here we are, carrying on with business as usual as if lives aren’t being ravaged every day by a virus our governments could’ve stabilized years ago.
Could climate change facilitate the creation of something worse: a parasitic fungal disease that turns us into zombies like The Last of Us? The seven scientists interviewed for this story all said no, that’s highly unlikely. The climate crisis is, however, already increasing the threat humans face from other sorts of fungal infections, the researchers clarified. What makes this threat all the more dangerous is that it isn’t operating alone.
What’s coming is a polycrisis—a monster worse than the fictitious zombies we obsess over because, this time, it’s real. The wave of crises won’t stop just because we’re already in one. In our world of fossil fuel pollution and corporate greed, crisis breeds more crises. With respect to public health, world leaders need to prepare for future outbreaks that will be embedded in this web of disasters, especially if they are going to protect society’s most vulnerable.
In The Last of Us, a strange fungus appears, driving humans to cannibalistic and violent behaviors. This is how it eventually spreads: the infected attacking the living.
In the video game, the fungus originates in South America where it infects crops before spreading elsewhere via spores, the microscopic particles fungus release to reproduce. The latest episode on Sunday seemed to confirm a popular theory on how the fungus first spreads in the game: that people are exposed through flour originating in Jakarta, Indonesia, before they infect one another.
Viewers get a glimpse of what the initial infection looks like in the show’s premiere where an old lady (the first zombie we see) has writhing branches protruding from her mouth, the mycelium threads from the fungus that has taken over her body. As the most recent episode depicted, these branches can grow larger and more elaborate in later zombie stages, eventually exploding from a person’s face. These zombies are called clickers, and the stages of infection only grow more gruesome from there.
Though the idea of human zombies is entirely science fiction, The Last of Us is inspired by a real-world phenomenon: zombie ants. In the game, the disease is called Cordyceps Brain Infection, or CBI. Ophiocordyceps (more popularly known as Cordyceps) is a genus of fungi that includes many species, many of which are parasitic. Biologists have described about 300 species in the genus, 35 of which can manipulate host behavior, said João Araujo, a curator in mycology at the New York Botanical Garden. They estimate that some 600 species may actually have the power to function as zombie fungi.
Ophiocordyceps unilateralis is a tropical species that targets ants. After an ant has contact with a spore, the fungus begins to move through its insides and eventually takes over its brain. At that point, the fungus is in control, so the zombified ant travels to higher treetops in the forest canopy before exploding with spores, sprinkling the fungus below.
“Eventually, a passing-by ant will get in contact with these spores and become infected, restarting the life cycle,” Araujo said in an email.
This can happen to other bugs, too—like fruit flies, an area studied by Dr. Carolyn Elya, a postdoctoral fellow at Harvard University. It dies similarly to the ants with the fungus, Entomophthora muscae, growing out of the fly’s exoskeleton, releasing spores into the environment.
The video game doesn’t mention climate change, but HBO’s adaptation of The Last of Us starts with a televised interview in 1968 where a scientist declares, “There are some fungi who seek not to kill, but to control,” speaking of the zombie ant. When the scientist sitting next to him challenges whether this can happen to humans whose bodies are too warm for these species of fungi, he responds: “Currently, there are no reasons for fungi to evolve to be able to withstand higher temperatures, but what if that were to change? What if, for instance, the world were to get slightly warmer?”
Well, we live in a warmer world now. Does that mean humans are next?
“This is pure fantasy (but so cool, right?),” Araujo said. “The fungus would require millions of years of genetic changes and adaptations in order to infect such a completely different group of organisms from what they are currently adapted to infect.”
Still, scientists still have a lot to uncover about these specific sorts of fungi, Elya at Harvard said in an email: “There is a ton that we don’t know about how these fungi alter host behavior. What’s great about shows like The Last of Us is that, in addition to entertaining folks, it can drive more awareness about the real natural phenomenon that inspired this story.”
“Mycology is one of the most neglected disciplines in biology and harbors one of the largest reservoirs for new discoveries.”
But it’s not just these parasitic fungi that control their hosts; scientists still don’t know enough about the kingdom of fungi as a whole. “Mycology is one of the most neglected disciplines in biology and harbors one of the largest reservoirs for new discoveries,” Araujo said. What they do know suggests that climate change may impact fungi in other ways. For instance, it may drive extinction across fungi species, said Dr. Patricia Ononiwu Kaishian, a mycologist and visiting biology professor at Bard College.
Extinction is rarely (if ever) a good thing. While parasitic fungi sound like a nightmare, there are plenty of beneficial fungi people need. Sure, we eat some mushrooms for dinner—but our bodies’ microbiomes are also full of fungi. Those actually do influence our brains and behaviors, Kaishian said. Scientists are still working to understand how exactly.
“The more we know about our microbiomes, the more we understand that these organisms do influence our moods and personalities,” she explained over email. “There are more fungal and bacterial cells in our body than human cells, and there is no complete understanding of our bodies without accounting for their influence.”
Trent Blizzard, president of the North American Mycological Association, also emphasized the medicinal and nutritional qualities of fungi. “Perhaps focusing on all the benefits they bring to humans and to our world, in general, would be more realistic than the science fiction of zombies,” he said via email.
Still, the public health sector can’t ignore the threat harmful fungi present. Rising temperatures are sure to alter where fungi can live, pushing them into new habitats and exposing new populations to them. The onslaught of floods, storms, and hurricanes that comes with climate change can also help disperse pathogenic fungi through wind or water, as outlined in a 2021 peer-reviewed study published in the journal PLOS Pathogens.
And this is where the danger lies.
In 2022, the World Health Organization published its first-ever list of fungi that threaten human health. Why? Well, they’re a “major threat,” to put it in the organization’s words.
At the moment, there aren’t enough medicines to treat these infections, which are building resistance to the treatments we do have. No single vaccine exists for these infections, which already kill about 1.7 million people a year. Meanwhile, globalization and climate change are expanding the range of these fungal diseases, pushing the WHO to prioritize research and policy intervention on the matter.
“We need to dramatically increase our investment of time, energy, and money in understanding fungi broadly and, specifically, combatting pathogenic fungi,” said Dr. Brian Lovett, an insect pathologist at the USDA Agricultural Research Service. “Lives are already at stake.”
The WHO categorized several fungi species by measuring their resistance to antifungal medicine and the number of deaths they cause. Many pathogens attack the lungs, brain, and blood. The ugly thing about fungal infections is their discriminatory nature. Not everyone faces the same risk of death. People with compromised immune systems are most vulnerable: people with cancer, HIV/AIDS, chronic disease, and organ transplants.
“That means that it can be particularly deadly and dangerous to these groups, but it also means that people aren’t paying attention to it because we’re talking about populations where we have to fight for airtime,” said Dr. Colin Carlson, an assistant research professor at Georgetown University’s Center for Global Health Science and Security.
These are also the same people who face high vulnerabilities from COVID-19, and world governments have made clear that their lives are not a priority. What’s more, research is finding that COVID-19 makes people, even those who were previously healthy, more susceptible to fungal infections.
As an example of a disease that needs more attention, Carlson pointed to valley fever, which is caused by a fungus historically found only in the desert soils of the Southwest. That fungus is now being found higher north in Washington state, likely due to climate change as the fungus prefers hot and dry environments. People become infected when they breathe in the fungal spores, which can cause flu-like symptoms.
The disease has disproportionately affected Indigenous peoples in the Southwest and incarcerated people in California—two groups that tend to see higher rates of illness that make them more vulnerable to contracting fungal infections. These communities aren’t responsible for any of these health issues, though. A failed healthcare system that ignores and marginalizes people who are low-income, Black, Indigenous, or of color is at fault here.
How can a sick person receive a diagnosis (much less treatment) if they can’t afford to visit a doctor? How are they supposed to feel safe visiting a doctor when history has shown them time and time again that they shouldn’t trust clinical institutions? How is a person who is incarcerated supposed to advocate for themselves when the state dehumanizes them?
“Fungal diseases are decently treatable, but they’re often misdiagnosed, or people don’t have access to healthcare,” Carlson said. “This is a lot of how you end up with things like the massive racial disparity in valley fever burden in Arizona. That is not an intrinsic property of the pathogen. It’s not even a direct property of climate change. It’s a property of inequality in the society we live in.”
The solution, of course, is quite simple: climate adaptation and preparation. That means leaving fossil fuels in the ground and implementing social safeguards, such as universal healthcare, Carlson urged. That was the thinking, after all, behind the now seemingly dead Green New Deal, a progressive political blueprint that put decarbonization strategies alongside social investments like affordable housing and green jobs training.
“Every single job we have should be a climate change job because that’s the biggest problem.”
David Hughes, a professor of global food security at Penn State University, used to study fungi and ant behavior, but he left that all behind to focus his efforts on the climate crisis instead. He was actually one of the consultants on the initial release of The Last of Us back in 2013. Now, he’s researching the ways climate change is impacting food systems, whose crops also face fungal infection risk but not the sort we see play out on The Last of Us. That’s what the public should focus on instead of science fiction, Hughes emphasized.
“Studying these things like the evolutionology of strange fungi in rainforests or making TV shows about them is all a waste of time; it’s all a distraction,” he said. “Every single job we have should be a climate change job because that’s the biggest problem.”
After all, climate change is affecting everything. Solving it won’t require smuggling a teenage girl across the country (as becomes the objective in The Last of Us). What the climate crisis does demand is political will for structural change and empathy for the communities already suffering.
Otherwise, we might as well be zombies chomping away at one another because the result will be mass death. People are already dying—in Pakistan, California, Kenya, and countless more places. And the cause isn’t only an airborne virus.
It’s a pandemic alongside multiple states of emergency due to record-breaking heat waves, blizzards, hurricanes, wildfires, monsoons, tornadoes, and landslides. It’s a pandemic alongside unprecedented weather events all while a war incites world leaders to consume more fossil fuels, not less.
The cause of death is a polycrisis, and it’s not coming. It’s already here. We’re living in it. What the world faces now dwarfs in comparison to the world our fossil fuel-obsessed leaders are creating by delaying climate action. Sadly, that future may not look much different than The Last of Us, after all. Except we wouldn’t have a parasitic fungus to blame—we’d only have ourselves.
