Have you watched the series yet?
“No I haven’t, but I did play the video game it’s based on. I want to watch the series though because I really enjoyed the game, not only because of how it’s made but also because it’s about fungi. I did watch the intro of the series and what’s really surprising is that the yellow thing you see there is not a fungus. It’s a slime mold, which is an entirely different organism.”
Ouch.
“Yeah, I saw it and was like: come on, that’s not a fungus!
The Last of Us is based on the fungus Ophiocordyceps unilateralis, which hijacks the behaviour of ants and turns them into zombies. How does that work?
“First, spores of the fungus infect the ant and the fungus starts growing in the ant’s body. After a while, the fungus starts changing the behaviour of the ant. The exact mechanism is unknown but recent studies didn’t find any fungal cells in the brain of the ants. Instead, the fungus uses bioactive compounds that interfere with the ant’s nervous system and control the ant’s muscles. The ant is pretty much aware of this but it cannot control its body anymore, which makes it even scarier.
“Eventually, the fungus hijacks the ant’s movement and makes the ant leave the nest and climb to a higher place. It bites a twig or leaf very hard – called a death grip – and then it dies. Researchers noticed that lighting, humidity and temperature are all very specific in that spot: they are the perfect conditions for the fungus to sporulate.”
Vasilis Kokkoris
In the series, global warming causes the fungus cordyceps to evolve and withstand the internal temperature of humans, infecting them and turning them into zombies. Could that happen in real life?
Well, it’s definitely a nice concept that the makers put together. It’s based on science, but exaggerated of course. To answer your question: something like this might be possible in a million years of co-evolution. It would require interaction with specific fungi and humans in a step-by-step process through many, many years of evolution. For instance, the hypothesis of the zombie ants is that it took 45 million years of evolution to occur. And humans are way more complex than insects.”
According to mycologist Vasilis Kokkoris, fungal infections in humans are really common. “We breathe in thousands of fungal spores every day. Our immune system is really well-equipped to make sure the fungi can’t survive. However, if your immune system is compromised, for instance by advanced cancer or serious cases of Covid, fungi could make you sick or could even lead to death.”
Imagine you were the scriptwriter, how would you make the series more realistic?
“Well, even if an infection like the one in the series would be possible, the parasite wants to survive. Therefore, it would have a way milder infection mechanism than in the series, so it doesn’t infect the entire human race. Because if the human race becomes extinct, the parasite also dies. It’s the same with the ants: only a small percentage of a colony gets infected, so the colony and the fungus both stay alive.
“On top of that, there’s a very interesting single-celled parasite that’s called Toxoplasma gondii. This parasite – not a fungus – can infect all warm-blooded animals, but it can only reproduce in felines such as house cats. It has been shown that this pathogen alters the behaviour of mice, it somehow changes the wiring of their brain. It causes the mice to lose their sense of fear and become attracted to the smell of cat urine. So they willingly go to their prey and are eaten by cats, causing the parasite to enter the cats and sexually reproduce.
‘Infections have been correlated to schizophrenia and road rage’
Now, to blow your mind even more, this parasite might also be altering the behaviour of humans. Because we have been living with cats for so long, the majority of people carry Toxoplasma gondii. Some studies found some eerie correlations, with infections being correlated to the frequency of schizophrenia, suicide attempts and road rage. We have to be careful because correlation doesn’t always mean causation. If you ask me, a scenario with this scary parasite would be more realistic.
That sounds scary, should we be afraid of fungi?
“No, I think we should be thankful for the extremely important and very diverse kingdom of fungi. Millions of years ago, fungi helped plants to colonize the land and caused a dramatic drop in the atmospheric carbon dioxide, basically making our planet habitable. Here at VU Amsterdam, we study this symbiotic relationship that still exists in every ecosystem. Also, fungi recycle dead plants and animals and turn them into nutrients for other organisms to take and grow. And fungi even produce our bread, wine, beer, and many of our medicines.”