The Last of Us is a new series from HBO that presents a dystopian post-apocalyptic world in which humanity has almost completely disappeared due to the outbreak of a dangerous infection that controls the brain and turns humans into bloodthirsty misshapen monsters.
The series presents two substantial differences with respect to typical movies like The night of the Living Dead o The Walking Dead: affected humans are not “undead” (zombies), but are alive; and the infecting organism is not a virus, but a fungus Ophiocordyceps that exists in real life.
Some manipulative mushrooms
The creators of the series and the video game on which it is based were inspired by an episode of the documentary Planet Earth. In it, an entomopathogenic fungus of the genus Ophiocordyceps infects a bullet ant (paraponera clavata), whose body it consumes inside leaving the brain intact, allowing it to manipulate the insect’s behavior.
More than two hundred species of Ophiocordyceps that can influence the behavior of insects. They were described in 1931 but, except for Tibetan farmers and in the Chinese domestic market where all kinds of organisms are traded, the Ophiocordyceps they were perfect strangers until just thirty years ago.
The strange case of Chinese athletes
September 1993. Sportswriters were impressed. In the Chinese national games held in Beijing, all the athletes in the sprints of 1,500, 3,000 and 10,000 meters broke the world record. Suspicion of the use of doping substances was immediately unleashed. The Chinese coach came out on top in an interview published in Track & Field News: no drugs. The secret was in training at altitude and in drinking an ancient concoction of traditional Chinese medicine.
It goes without saying that the search for that drink was unleashed, and even more so when it was learned that it also had aphrodisiac properties. He was immediately labeled the “viagra of Tibet”. The organic base of the miraculous potion was “yarsagumba”, a worm-fungus that grows between 3,000 and 4,000 meters of altitude in the Tibetan alpine meadows.
In reality, as if it were the mythological centaur, the yarsagumba is a chimera made up of the body of a ghost moth caterpillar. Thitarodes armoricanusmummified after being invaded by the fungus Ophiocordyceps sinensiswhose mycelium develops from spores existing in the soil.
During the fall, the mycelium infects the live caterpillar which grows underground and invades its body. In order to grow, the fungus absorbs all its nutrients from the caterpillar’s body. By the summer of the following year, after consuming it completely, the infection has killed the caterpillar, but left its skin intact.
Meanwhile, the fungus transforms into a hardened mass, the sclerotia, which retains the shape of the caterpillar’s body and pushes it with its head pointing upwards until it is a few centimeters below the soil surface.
Just before winter begins, from the head of the caterpillar, which remains buried in the ground, an erect structure emerges from the ground, the stroma. On this there are some crateriform structures, the perithecia, inside which the spores develop that will renew the cycle once autumn arrives, when the subterranean larvae that emerged from the eggs buried by the butterfly in late spring begin to develop.
For centuries, the mushroom has been coveted in Asia due to its medicinal and aphrodisiac properties. The uses of yarsagumba in traditional Chinese medicine have been extensively researched in the Orient. It has been successfully used in studies with animals and in clinical treatments with humans, among which its therapeutic use stands out as part of the antiretroviral treatment in patients with the HIV virus, which is based on an exclusive active principle of this fungus, the nucleoside didanosine. .
Can these fungi cause a pandemic like covid-19?
A fungal pandemic comparable to covid-19 is highly unlikely for several reasons.
First of all, although there are some microscopic fungi whose infections can be fatal and although some of them appear in cancerous tumors, fortunately most fungi do not affect humans at all. This does not mean that fungal infections kill the same number of people each year as tuberculosis.
For the most part, potentially lethal fungi are opportunistic pathogens. This means that we usually live with them without causing us problems, because they only take root in vulnerable people who are immunosuppressed by an underlying disease such as cancer, by a viral infection such as HIV, and even by the abuse of antibiotics, three factors that increase the risk of dangerous fungal infections.
Third, most fungi are mesophilic, growing at cool temperatures of around 10⁰C, which means that they cannot normally grow at the internal temperature of the human body. That is one of the reasons why most fungal infections are usually superficial dermatomycoses.
For the rest, all Ophiocordyceps Known insects are specific to certain insects (which have a body temperature identical to that of the air around them) and are not adapted to thrive at our body temperature nor can they compete with our immune system, much more complex and evolved than that of an insect.
A WHO report and some recent research based on the almost simultaneous appearance on three continents of White earsa yeast capable of causing life-threatening infections, suggest that climate change may be increasing the geographic distribution of some pathogens and causing more fungal infections in mammals and humans.
This is something that experts already knew when they predicted it three decades ago. Rising global temperatures mean fungi must adapt, which could hypothetically increase the number of species potentially causing serious human infections.
As suggested by one of the characters in The Last of Us, climate change may be raising new pandemic scenarios. Once again, reality may be stranger than fiction.