Humanity has lost. Twenty years earlier, she was hit hard by a devastating epidemic caused by the pathogenic fungus Cordyceps, and is now divided between a few survivors and infected who have turned into zombies. Based on a video game released in 2013, The Last of Us (currently airing on HBO/Amazon Prime Video) follows 40-year-old Joel and young Ellie on their perilous journey through a devastated America. Very successful, it offers an original take on zombies, as the infestation here is fungal.
But how much scientific truth is there in this? Can cordyceps really threaten the human race?
Cordyceps is a genus of entomopathogenic fungi (that is, infecting insects), of which there are more than 600 species, most of them in Asia: Nepal, China, Japan, Korea, in particular. When cordyceps attacks an insect, the mycelium of the fungus gradually invades and replaces the host tissue. Some species are even able to take control of the parasite, causing it to infect other insects. To do this, fungal outgrowths will appear on the body of the animal, which will release many infectious spores.
“This is also the first criticism that can be made of the series,” analyzes Luis Portillo, a cordyceps specialist at the University of Montpellier. Infection does not occur through spores, as in reality or as in the original game, but through bites, like in a classic zombie … “
On this point, the writers of the series made excuses, explaining that they were forced to change the mode of infection compared to the game, which would force the actors to wear a protective mask at all times, which would harm the visual look and immersion in the story.
An extremely rare and genetically fragile mushroom.
Yet in many ways, fiction has blithely separated from reality. “We are focusing on the one-sided cordyceps that infects ants,” the researcher continues. It mostly affects isolated people or people late in life whose immune systems are less efficient. But it turns out that this is an extremely rare mushroom. C. unilateralis was observed once in 1892, then in Germany in the 1970s, but no more. Since then, no one else has found it … The reason is that it is ineffective. Of course, we can imagine catastrophic scenarios, but biological reality catches up with us: this fungus has several flaws that prevent it from being a serious threat. The temperature in the first place, ideally 18°C, but we have more than 20°C in the brain. And let’s not talk about the rest of our body at 37°C…”
Even assuming that the mutation gives Cordyceps the ability to grow at 37°C, Luis Portillo sees a second limitation: “the humidity must be close to 100% for the fungus to survive.” This is the reason why it thrives in humid areas and rainforests.
Another weakness of Cordyceps is its genetic fragility. Unlike, for example, the Paris mushroom, which can be propagated indefinitely, the same cannot be said for cordyceps: after three generations, its genome deteriorates. “Imagine that I can get infected,” says Luis Portillo. “I will infect you. You will infect a third person, but things will not go further. Due to the degradation of the genome, transmission will be stopped!