The long-awaited HBO series ‘The last of us’, Inspired by the video game of the same name, it presents a dystopian future after an epidemic caused by a fungus, Cordycepswhat has mutated due to global warming. The human hosts lose control of themselves and become zombies ready to lash out, devour, and infect anyone who crosses their path. The plot is a fantasy, but Cordyceps exists and in real life it also behaves quite sinisterly.
This genus of fungi encompasses some 500 species throughout the world, most of them in tropical areas of Asia (precisely, in fiction the first cases begin in Jakarta, Indonesia) and America, where they have sufficient temperature and humidity to develop well. «In general they are insect parasitic fungi: wasps, ants, locusts… They are very striking because they form a fruitful body, a mushroom, on the corpse,” Javier Diéguez, a CSIC researcher at the Royal Botanical Garden of Madrid, explains to this newspaper.
Fungi produce a series of enzymes, proteins that degrade other proteins, in such a way that they break the exoskeleton of insects to colonize them. With their nervous system altered, the insects lose their will and become puppets of the fungi, which, after a while, force them to go to a suitable area of the ecosystem, such as open spaces or the highest tips of plants. , to disseminate their spores and colonize other insects. Once the objective is achieved, the host dies gruesomely, with the body completely pierced by the mushrooms.
Cordyceps sprouting from a wasp
“It is very morbid, but it is a complex life cycle, the result of evolution, to find the most efficient path for the survival of the species”, explains the researcher. A manipulated organism may seem like science fiction, but we may not be free either. “We are beginning to understand how our behavior is influenced by the bacteria in our gut flora,” he adds.
threat to diversity
In recent decades the number of species infected by fungi has increased “exponentially”. According to Diéguez, it is a phenomenon that, like Covid-19, has been driven by globalization. In this case, due to the introduction of affected invasive species that have wreaked havoc: river crayfish are on the brink of extinction; a third of the world’s amphibians and some of its fish have disappeared, and sea turtle eggs suffer massive die-offs. Aspergillus, for example, is considered to be the culprit in the disappearance of corals. Fungi are “one of the main threats to diversity,” says the researcher.
The question is, Could fungi change human behavior? As Diéguez explains, neither mammals nor birds have fungal diseases “because we regulate our temperature. Mushrooms grow poorly above 32ºC.” Only one exception is known: several species of bats in the US, which suffer from the white nose disease (SNB). When they hibernate, a fungus introduced from Europe (Pseudogymnoascus destructans) colonizes the coldest part of their body, which is the nose, and they die.
Thanks to the fact that we are warm-blooded animals, fungi are not a big problem for humans, except in two cases: burned and immunosuppressed. “During chemotherapy, our immune system is weaker and body temperature drops, so a fungal infection could be serious,” warns Diéguez. Similarly, some fungi, such as Aspergillus, can also cause lung disease and cancer. «It is even suspected that the curse of the pharaohs -the deaths of the discoverers of their tombs-, could be related to fungi. They were buried in closed areas with high humidity,” says the scientist.
Climate change
In the series, Cordyceps has mutated to adapt to life in higher temperatures, a consequence of climate change, allowing it to subdue humans. Diéguez believes that, in effect, climate change will select the most resistant fungal species and perhaps they will be able to colonize us. But “they are evolutionarily complex conditions that take many years to occur. And at the rate we’re going I don’t think our species is going to survive that long,” he says. Even if it did, fungi lead their hosts to a horrible and inevitable death, but none cause them to attack another member of their own species.
However, these parasites can represent a threat to our species from another point of view. “We have simplified agriculture by planting the same thing all over the world: wheat, rice, olive trees… If a fungal disease were to wipe out one of these crops, it would devastate our food base,” he warns.
If someone starts to fear Cordyceps after watching the series, they can calm down. It is a common component of some health supplements and, as far as is known, no one has ever bitten their neighbor for taking them. Not forgetting that bread and beer and other yeast foods are made with mushrooms. Of course, in line with other stories of the genre, ‘The last of us’ recalls that altering the rules of the game of nature produces monsters. And that is a very real fear.