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!
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. In France we can find a dozen species in the wild. 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.
“In addition, this is the first reproach that could be made for the series,” analyzes Luis Portillo, a cordyceps specialist in the laboratory of botany, phytochemistry and mycology of the pharmaceutical faculty of 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 … “
Pedro Pascal in The Last of Us. HBO/Prime Video credit
On this occasion, the writers of the series justified themselves by saying that they were forced to change the infection mode from the game, which would force the actors to wear a protective mask at all times, which would harm the visual look and immersion of 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, and our body is 37 ° C … “
Even imagining that a “miraculous” mutation allows Cordyceps to grow at 37°C, Luis Portillo sees a second limitation: “the humidity must be close to 100% for the fungus to survive.” blooms in autumn in Europe in humid areas and tropical forests.
Another weakness of Cordyceps is its genetic fragility. Unlike, for example, champignon, which could be propagated indefinitely, this cannot be said about cordyceps: after three clonings, its genome deteriorates. “Let’s imagine that I could be infected,” says Luis Portillo. I will infect you. You will infect a third person, but it will not go beyond that. Due to the degradation of the genome, preventing the growth of its cells, the transmission will be stopped! In addition, it is very sensitive to inbreeding: crossing between spores of the same individual rarely produces viable offspring.
Other much more dangerous parasites
Despite the monstrous and visually very impressive transformations to which it subjects insects, Cordyceps is far from being an absolute parasite. “This fungus has been around for 48 million years,” says the scientist. However, in all this time, he has never managed to bypass the immune system of insects, since he still cannot infect healthy people.
Moreover, in terms of pathogenic fungi, there are more formidable ones that directly threaten the human race. University of Montpellier. Those that cause superficial skin infections, the best known of which is nail fungus. Those that cause more serious, deeper infections, such as the lining of the vagina, or mouth infections (oral thrush) caused by Candida albicans, a yeast. For people with a weakened immune system as a result of cancer treatment or diseases such as AIDS, these types of infections can be quite serious. Finally, the third type of mycoses concerns deep mycoses. Again, very dangerous for immunocompromised people.”
These infections can mainly occur through food. But they can also be inhaled. Indeed, our environment is saturated with yeast and mold spores that we constantly breathe. “In this context, the most dangerous species is by far the Aspergillus genus, which affects the lungs and can spread throughout the body. But otherwise, most of these spores are harmless, since our body is too hot for them to grow.
Pathogenic fungi are carefully controlled in hospitals
However, in hospital departments, these fungi are under close observation. Patients with a weakened immune system are placed in a sterile ward, their food and drink are controlled.
Since 2009, the date of the description of the first human infection, the most monitored yeast remains Candida auris, responsible for epidemics in hospital wards. For the CDC, the US Centers for Disease Control, Candida auris, currently multi-resistant to the three available classes of antifungal drugs, poses a “serious global threat to human health.”
In fact, for humans, cordyceps is more of an opportunity than a threat. “Cyclosporine, a very valuable immunosuppressive agent for organ transplantation, was isolated from a fungus related to Cordyceps,” recalls Françoise Fons, head of the laboratory of botany, phytochemistry and mycology at the University of Montpellier. Another interesting compound in human medicine is fingolimod, used in the context of multiple sclerosis. It is an improved derivative of a myriocin compound produced by another fungus, Cordyceps sinclarii, an entomopathogenic fungus that parasitizes cicada nymphs.”
Cordyceps is considered an aphrodisiac in the Chinese Pharmacopoeia.
In the Chinese Pharmacopoeia, cordyceps is even considered an aphrodisiac because of its stimulant properties. This is a precious and expensive dish, because it is rare, it was offered to members of the imperial elite of the time of the emperors. Tested for antioxidant, anti-inflammatory and antimicrobial activity, different types of cordyceps have protective properties for various organs such as the kidneys, lungs, liver, brain. They are also the subject of much research, especially in the field of cancer treatment. “During the Beijing Summer Olympics in 2008,” Françoise Fons clarifies, “controversy arose about some players who were “doped” with cordyceps-based nutritional supplements…”
And some scientists even argue that cordyceps could be our best ally in conquering the planet. “Indeed, says Luis Portillo, the fall of a giant asteroid 66 million years ago caused a massive cooling of the planet. According to explorer Merlin Sheldrake’s theory, dinosaurs, cold-blooded animals already weakened by this drop in temperature, could have been infected with Cordyceps, which would have found fertile ground in them to spread. Without the help of Cordyceps, mammals and the human species would not have been able to reproduce as strongly.”