From 2012 to 2015, a strain of the fungus that could infect humans independently appeared on three continents.
I’ve been watching the HBO series “The Last of Us,” just like a lot of other people. The story follows Joel (played by Pedro Pascal) and Ellie (Bella Ramsey) as they travel across the former United States during the zombie apocalypse (now run by a fascist government called Fedra). I love reading post-apocalyptic and zombie fiction.
I was also expecting engaging storytelling because my husband had told me how well-written the plot is in the video game that served as the Last of Us series inspiration. I didn’t anticipate being so fascinated by the science that underlies science fiction.
Two scientists on a fictitious 1968 talk show discuss the microbes that give them pandemic nightmares in the first minutes of the television show of The Last of Us series. One person claims that fungi, not bacteria or viruses, are the cause of his insomnia.
He claims that the fungi that control their hosts rather than consuming them are especially dangerous. He uses the example of fungi that manipulate insects by flooding their brains with hallucinogens, turning them into living zombie ants.
In The Last of Us series, he continues by stating that even though our body heat keeps us fungus-free, if the world got a little bit warmer, that might not be the case. He believes that as the temperature rises, an insect-stealing fungus could mutate a gene that would enable it to enter human brains and seize control.
He claims that such a fungus could persuade its human puppets to spread it “by any means necessary.” And to make matters worse, there are no available treatments, cures, or preventative measures.
Despite it being only a short while, I became engrossed. Everything sounded so terrifying and believable. After all, people are already susceptible to fungi such as those that cause ringworm, yeast infections, and nail infections.
I therefore sought the advice of some specialists in fungi to determine whether this was actually possible. I was curious to know if global warming has caused any fungi to mutate and spread disease. I then gave Arturo Casadevall a call.
He has been considering heat and fungi for a while. He has suggested that the pressure on evolution that led mammals and birds to develop warm-bloodedness may have come from the need to prevent fungal infections.
At human body temperature (37° Celsius, or 98.6° Fahrenheit), the majority of fungal species simply cannot reproduce. But as the planet warms, “these strains either have to die or adapt,” says Casadevall, a microbiologist at the Johns Hopkins Bloomberg School of Public Health who specializes in fungal infections.
This suggests that fungi that currently infect insects or reptiles may evolve to grow at temperatures more similar to those of the human body.
The average body temperature of people has also decreased since the 19th century, at least in high-income nations, according to research published in the journal eLife in 2020. According to one British study, the average body temperature is 36.6 ° C (97.9 ° F). Some of us are even cooler than that.
According to Casadevall, the potential for fungi to adapt to higher temperatures and the cooling body temperatures of humans are in direct conflict. Evidence of one such crash was presented by him and his colleagues. A deadly fungus known as Candida auris may have been able to adapt to human body temperatures as a result of climate change.
From 2012 to 2015, a strain of the fungus that could infect humans independently appeared on three continents. “It’s not like someone spread it on a plane. At the same time, these events appeared out of nowhere,” says Casadevall.
Climate change will lead to a selection event in which many fungi will die but some will survive, and their offspring may be able to survive until human body temperature is no longer a challenge.
Fungi that infect people are usually not picky about their hosts, and can grow in soil or in people, pets, or other animals. The reason they don’t infect people more often is that they have no need of us, and the immune system usually keeps them in check.
However, fungal infections can cause serious illness or be deadly, particularly to people with weakened immune systems.
The second episode of The Last of Us series reveals that the zombie-creating fungi initially spread through people eating contaminated flour. In real life, most human infections arise from breathing in spores, but Casadevall says it’s “not implausible” that people could get infected by eating spores or by being bitten.
Asiya Gusa, a fungal researcher at Duke University School of Medicine, has published a paper on how one fungus mutated at elevated temperature to become harder to fight.
Cryptococcus deneoformans, which already infects humans, became resistant to some antifungal drugs when grown at human body temperature. The resistance was born when mobile bits of DNA called transposons hopped into a few genes needed for the antifungals to work.
Gusa and colleagues grew C. deneoformans at either 30° C or 37° C for 800 generations, long enough to detect multiple changes in their DNA.
Heat stress accelerated the growth of the fungi, with one type of transposon accumulating a median of 12 extra copies of itself in fungi grown at body temperature. By contrast, fungi grown at 30° C tended to pick up a median of only one extra copy of the transposon. The team reported their results January 20 in PNAS.
The researchers don’t yet know the effect of these transposon hops on the fungi’s ability to infect people, cause disease, or resist fungus-fighting drugs.
Charissa de Bekker and Jui-Yu Chou are two researchers who study the Ophiocordyceps fungi that are the model for the TV show’s fungal menace. These fungi infect ants, flooding them with chemicals that steer them to climb plants.
Unlike most fictional zombies, the ants are alive during this process, and the fungi even help preserve the ant while it is feeding on it. When the ant dies, a mushroom rises from the corpse, showering spores onto the ground where other ants may become infected.
Numerous species of ants and other insects are infected by related Ophiocordyceps species. But each type of fungus has a very specific host that it infects. This is due to the fact that the fungi had to tailor the chemicals they produced to each species they infected. The inability to infect multiple species is sacrificed for the ability to manipulate behaviour.
According to Chou, a researcher on fungi at Taiwan’s National Changhua University of Education, a fungus that specialises in infecting ants can’t likely survive the immune systems of people. “Consider a key that opens a certain type of lock. Only this particular combination will cause the lock to open “He claims.
Fungi have evolved to withstand human body temperature and immune system attacks, but they cannot take control of our minds. It took millions of years of coevolution for the fungi to master piloting ants, and Casadevall agrees that fungi that mind control insects probably won’t turn humans into zombies.
Antifungal drugs exist and cure many fungal infections, but some infections may persist, and some fungi are evolving resistance to the drugs. A few fungal vaccines are in the works, but they may not be ready for years. Infected ants don’t turn into vicious, biting zombies but instead show “social immunity” to protect the rest of the nest from infection.
The experts I spoke with expressed their hope that the program would raise awareness of actual fungal diseases. Gusa was particularly happy to see fungi getting attention. She also enjoys the Last of Us series opening in which a scientist speculates that climate change may give rise to mind-controlling fungi that aim to infect everyone on the planet.
She claims that when she watched the Last of Us series introduction, she was practically yelling at the television out of excitement. “The threat of fungi developing thermal adaptation is the basis for a large portion of my grant funding. It was amusing to watch it play out on the screen.”
Originally published at ScienceNews