Like so many others, I watched the HBO series The last us. The classic zombie apocalypse drama follows Joel (played by Pedro Pascal) and Ellie (Bella Ramsey) as they travel through the former United States (now run by a fascist government called Fedra).
I’m a big fan of zombie and other post-apocalyptic fiction. And my husband told me how good the storyline is in the video game that inspired the series, so I’m ready for some interesting storytelling. What I didn’t believe was behind sci-fi so much.
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In the opening minutes of the series, two scientists are shown talking in the fictional 1968 show discussing the microbes that plague them in their nightmares. He says that they are fungi that are not viruses or bacteria – they keep watch. The most worrisome, he says, are fungi, which control rather than kill their hosts. He gives the example of mushrooms that turn ants into living undead, car insects with hallucinogens infused into their brains.
He goes on to warn that although the human body’s body temperature keeps us free from fungus, that cannot be true if the world is a little warmer. He predicts that as the thermostat climbs, a fungus that hijacks insects can change genes allowing it to be implanted in the human brain and take over our minds. Such a fungus could introduce its human robots to the fungus “by any means necessary,” he said. What is worse, there are no preventions, no treatments, or remedies, and they are not being done in any way.
The segment is short, but it had me hooked. It all sounded so cool and… likely. After all, the same fungi that cause nail infections, yeast infections and ringworm already infect people.
So I consulted some experts on fungal infections to find out if this was possible.
I have good news and bad news.
First, the bad news.
The bad news: Climate change has already helped one fungus mutate to infect humans.
I wanted to know if the heating caused some fungi to mutate and become infectious. So I called Arturo Casadevall. He thought for a long time about fungi and heat. He proposed that the need to avoid fungal infections may have provided the evolutionary pressure that led mammals and birds to develop blood yeast (SN: 12/3/10).
Most fungal species simply cannot reproduce the human body temperature (37° Celsius or 98.6 Fahrenheit). But as the world warms, “these species must either die or adapt,” says Casadevallus, a microbiologist who specializes in fungal diseases at the Johns Hopkins Bloomberg School of Public Health. It raises the possibility that fungi that currently infect insects or reptiles may be able to grow at temperatures closer to that of the human body.
At the same time, people’s average body temperature has increased since the 19th century, at least in high-income countries, the researchers reported. eLife in 2020. One study pegs the UK’s average body temperature at 36.6° C (97.9° F). And some of us are even cooler.
Fungi can adapt to higher heat and cool the body temperature of humans during a collision, Casadevall says.
He and his colleagues produced evidence of one such collapse. Climate change has allowed a deadly fungus White ears acclimatization to human body temperatures (SN: 7/26/19). A version of the fungus that could infect humans independently emerged on three continents from 2012 to 2015. “It’s not like someone just spread out on a plane. These things never came out at the same time,” Casadevallus says.
Some argue that the planet has not warmed enough to solve the problem, he said. “But think about all the really hot days [that come with climate change]. Every day is a really hot reading event “in which many fungi die. But some of those fungi will have changes that help them handle the heat. They will escape. Their offspring will be able to survive even hotter heat waves until the temperature of the human body is no longer a challenge.
Fungi that infect humans aren’t usually picky about their hosts, says Casadevall. They grow in the soil or – if given the opportunity – in humans, pets or other animals. The reason fungi don’t infect humans is because the world is much colder than us, and they don’t need us, he says.
When people become infected, the immune system usually keeps the fungus at bay. But fungal infections can cause serious illness or even be fatal, especially in people with weakened immune systems (SN: 11/29/21; SN: 1/10/23).
The second event The Last of Us indicates that the fungus initially causes zombie-creation by eating contaminated food. then infected people invade and bite others, shedding the fungus.
In real life, most human infections arise from breathing in spores. But Casadevallus says it’s “not improbable” that humans could become infected by eating spores or being bitten.
Even worse: Fungal genes can adapt to higher temperatures.
And I was totally surprised how the fungus could develop in response to the heat. Asiya Gusa, a fungal researcher at Duke University’s school of medicine, published one possibility.
In 2020, she and her colleagues resigned Journal of the Academy of Sciences how a single fungus changes at elevated temperature to become more difficult to fight.
Cryptococcus deneoformans; which already infects humans (albeit a zombie-maker), are resistant to some antifungal drugs that have grown in the human body at room temperature. Resistance is born when bits of mobile DNA called transposons (often called jumping genes) jump into the few genes necessary for antifungals to work.
In subsequent studies, Gusa and colleagues grew C. deneoformans or 30° C or 37° C for 800 generations, it is long enough to detect multiple mutations in their DNA. The fungi have no problem growing at a balmy 30° C (86° F), the temperature at which researchers typically grow fungi in the lab. But their growth slowed in the higher temperature, a sign that the fungi were stressed by the heat.
In C. deneoformansas heat stress really jumps out. One type of transposon accumulated a median of 12 extra copies of itself in fungi grown at body temperature. Fungi, however, grown at 30°C to collect a median of only one extra copy of the transposon. The team announced those results on January 20 PNAS. Researchers do not yet know the effect transposon hops may have on fungi’s ability to infect humans, cause disease or resist fungus-fighting drugs.
So remember, bad news isn’t great. Fungi are changing in the heat and at least one species has gained the ability to infect humans due to climate change. Other fungi that infect humans are more widespread than in the 1950s and 1960s, even as the world warms (SN: 1/4/23).
But I promised good news. And here it is.
The good news: The human brain can resist zombification.
It may not be our body temperature, but brain chemistry that protects us from being hijacked by zombifying fungi.
I tracked down two researchers, Charissa de Bekkero and Jui-Yu Chou Ophiocordyceps fungi that are a model in the fungal threats show. These fungi infect ants, flooding the insects with a cocktail of chemicals that direct the ants to climb the plants. Once in the ant position they collapse and hold the muscles locked in place (SN: 7/17/19).
Unlike most fictional zombies, ants live in this process. “Many people get the misconception that we work with dead ants,” says de Bekker, a microbiologist at the University of Traje in the Netherlands. He’s happy to see the show “very much alive in the history of the military while his character is changing.” The mushrooms also keep the ants alive while they feed on it. But at last the ant dies. The fungus then rises from the corpse, spreading its spores on the ground where other ants are infected.
Kindred species of Ophiocordyceps they infect various species of ants and other insects. However, each fungal species is very specific to the host it infects. This is what fungi use to individualize their economies, as they infect particular species. The ability to treat behavior comes at the cost of not being able to infect multiple species.
A fungus that specifically infects ants probably can’t get past people’s immune systems, says Chou, a fungal researcher at Changhua National University of Education in Taiwan. “Think of a key that fits into a specific lock. This is the only combination that will open the lock,” he said.
Even though fungi evolved to support the human body’s temperature and attack the immune system, they probably couldn’t take over our minds, says de Bekker. “Manipulation is like a whole ballgame. You need to have a ton of additional tools in there.” It took millions of years of evolution for fungi to pilot ants, after all.
While fungi produce alchemical mind-altering agents that can affect human behavior (eg LSD and psilocybin), Casadevall agrees that fungi that control the mind of insects are unlikely to turn humans into zombies. “There is no copper,” he said.
Infected ants do not turn into vicious or biting zombies, says Bekkero. “If anything, we’re actually seeing healthy ants attacking infected people, and once they’re infected, it’s like basically removing them.” That “social immunity” helps to protect the rest of the nest from infection.
Also good: People are interested enough to develop treatments.
The poetic saying that we cannot prevent, treat or cure these fungal infections is also a stretch.
Antifungal medications exist and can cure many fungal infections, although some infections may persist. Some things that have spread to the brain can be extremely difficult to clean up. Fungi also develop drug resistance. A few fungal vaccines are in the works, although they haven’t been ready for years.
Experts I spoke with said they hope the show will bring attention to real fungal diseases.
Gusa was especially happy to see the mushrooms in the limelight. And she shares my indulgence in that opening sequence in which a scientist predicts that climate change may continue to cause mind-controlling fungi to infect every human being on the planet.
“I was pretty much crying on TV when I was watching [show’s] inwardly, in an excited manner, he said. “This is the basis of much of my grant funding… the threat of adaptation of chocolate fungi. …
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