The Last of Us is a classic zombie apocalypse drama starring Joel (played by Pedro Pascal) and Ellie (Bella Ramsey) as they journey across the former United States (now headed by Fedra).
I like zombie and other post-apocalyptic fiction. My husband had mentioned how great the storyline in the video game that inspired the series, so I was expecting for interesting storytelling. What I didn't expect was to be so interested in the science behind the sci-fi.
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Two scientists on a fictional 1968 talk show discuss the microbes that keep him awake, rather than viruses or bacteria. Especially worrisome, he says, are the fungi that control rather than kill their hosts, as he puppeteers ants with hallucinogens.
Even if human body temperature kept us fungus-free, this might not be true if the world got a little warmer. A fungus that hijacks insects may mutate a gene capable of gaining access to human brains and controlling our minds, according to the author. There are no preventatives, therapies, or cures, nor a mechanism to accomplish them.
Although it is a brief segment, it captivated me. Everything sounded so chilling and... plausible. After all, fungi like ones that cause nail infections, yeast infections, and ringworm already infect people.
To investigate whether or not this might be the case, I consulted some experts on fungal infections.
I have good and bad news.
First, the bad news.
I wanted to know if warming has induced any fungi to alter and become infectious. So I contacted Arturo Casadevall. He believes that the need to avoid fungal infections may have fueled mammals and birds to develop warm-bloodedness (SN: 12/3/10).
Most fungal species simply can't reproduce at human body temperature (37° Celsius) or 98.6° Fahrenheit. However, as the world warms, "these strains either have to die or adapt," according to Casadevall, a microbiologist who specializes in fungal infections at John Hopkins Bloomberg School of Public Health.
In 2020, researchers in the United Kingdom estimated humans' average body temperature to be 36.6° C (97.9° F). Other people are even cooler.
Casadevall claims that Fungi's possible adaptation to higher heat and humans' subdued body temperature are on a collision course.
Climate change may have allowed a deadly fungus called Candida auris to adapt to human body temperatures (SN: 7/26/19). From 2012 to 2015, a different form of the fungus that might infect humans emerged on three continents simultaneously, according to Casadevall.
'But you have to think about all the really hot days that come with climate change,' says one man. Some of those fungi will die, but their offspring may be able to weather future much hotter heat waves.
Casadevall claims that fungi that infect people are usually wary about their hosts. They may grow in soil, in people, pets, or in other animals if given an opportunity. "The world is much colder than we are, and they have no need of us," says the fungi.
Fungal infections can be fatal, especially to people with weak immune systems, when people get infected.
The zombie-creating fungi first spread through people who ate contaminated flour, then those who are infected attack and bite others, spreading the virus.
Most human infections arise from breathing in spores in real life, but Casadevall claims that eating spores or being bitten is "not implausible."
Asiya Gusa, a fungal researcher at Duke University School of Medicine, has studied one possibility.
She and her colleagues published a paper in the Proceedings of the National Academy of Sciences on how a plant mutated at high temperature became more difficult to fight.
When grown at human body temperature, Cryptococcus deneoformans, which already infects humans (though it isn't a zombie-maker), became resistant to antifungal medications. The adaptation came about when mobile DNA fragments called transposons (often called jumping genes) joined together to form the antifungals' binding proteins.
Gusa and colleagues maintained C. deneoformans at either 30° C or 37° C for 800 generations, long enough to notice many changes in their DNA. Fungi had no problem growing at the mild 30° C (86° F), the temperature at which researchers typically grow fungi in the lab.
That heat stress really sent C. deneoformans flying. fungi grown at body temperature accumulated a median of 12 additional copies of themselves. By contrast, fungi grown at 30° C tended to pick up a median of just one additional copy of the transposon.
The bad news isn't great. Fungi are mutating in the heat, and at least one species has become capable of infecting people thanks to climate change. Other fungi that infect people are much more widespread than they were in the 1950s and 1960s, also because of a warming world (SN: 1/4/23).
I promised good news, and here it is.
It's not our body temperature, but our brain chemistry that protects us from being hijacked by harmful organisms.
Charissa de Bekker and Jui-Yu Chou, two researchers studying the fungal menace posed by the TV show. These insects are infected with a cocktail of chemicals that propel them to climb trees (SN: 7/17/19).
Unlike most fictional zombies, the ants remain alive throughout the process. De Bekker, a microbiologist at Utrecht University in the Netherlands, is glad to see the program "stick to the story of the host being very much alive while its behaviors change." However, eventually the ant dies, and a mushroom rises from the corpse, spraying spores on the ground where other ants may become infected.
Ophiocordyceps is a related species that infects a variety of insects and ants. Despite this, each fungal species is very specific to the host it infects. That's because the fungi had to personalize the chemicals they use to control the particular species they infect.
Chou, a fungal researcher at the National Changhua University of Education in Taiwan, believes that a fungus that is adept at infecting ants might be unable to get past humans' immune systems. Only this unique combination will open the lock, he says.
De Bekker notes that even if fungi could be trained to withstand human body temperature and immune system attacks, they would not be able to control our minds. “Manipulation is a totally different ballgame. You need a ton of additional equipment to get there.” After all, it took millions of years for the fungi to master piloting ants.
Casadevall agrees that fungi that mind control insects will likely not transform humans into zombies.
De Bekker adds that infected ants don't turn into vicious, biting zombies. "We actually see healthy ants being aggressive toward infected individuals once they discover that they're infected, to basically remove them." That "social immunity" protects the rest of the nest from infection.
The claim by a fictional scientist that we would not be able to prevent, treat, or cure these fungal infections is also a stretch.
Antifungal medications are available, although some infections may remain. Some that extend to the brain may be difficult to clear. A few fungal vaccinations are in the works, although they may not be ready for years.
Experts I spoke to said they hope the program will educate people about actual fungal diseases.
Gusa was particularly interested in seeing fungi in the spotlight. She also shares my fondness for the backwaters of the 1960s when the scientist predicted that climate change might result in mind-controlling organisms capable of infecting every individual on the planet.
"I was pretty much yelling at the TV when I saw the [show's] intro," says the lady. "This is the foundation of a lot of my grant funding... the danger of thermal adaptation of fungi.... It was a pleasure to see it play out on the screen."