Is Cordyceps the biggest threat to humanity?

We answer the main question that remained after the first season of The Last of Us.

What happened?

The first season of the TV series The Last of Us has ended. The action takes place in a post-apocalyptic world where the cordyceps fungus has learned to turn people into contagious “zombies” rather than ants, as before. According to the plot, the rise in global temperatures caused cordyceps to rapidly evolve and adapt to the temperature of the human body. Critics are delighted, viewers are as well, and even fans of the video game on which the show is based seem to have enjoyed it.

All this is great, but there is one small question left: Can mushrooms really turn people into zombies?

And what, can they?

No, you can sleep peacefully. Although the plot of the series (and game) is based on a real family of fungi-cordyceps, humans have nothing to fear. Cordyceps infects only certain insects and cannot turn a human into a zombie.

Mushrooms from the genera Cordyceps and Ophiocordyceps grow all over the world in tropical, subtropical, and even temperate forests. They infect insects, such as ants, and essentially turn them into “zombies”. The fungi manipulate the nervous system of their victims, forcing them to spread their own spores. It may sound creepy, but there is nothing for humans to fear.

Screenwriters also indulged in other artistic exaggerations: in real life, cordyceps does not compel its victims to bite for the spread of infection, and infected individuals do not connect with each other in a network.

You say that cordyceps is only dangerous to insects. But how exactly does it affect them?

At first, the spores of the cordyceps attach to the exoskeleton of the ant and climb inside its body, turning the victim into a obedient “puppet”. To achieve this, the fungus releases bioactive compounds that affect the ant’s nervous system and control its movements.

As the infection spreads, the ant is forced to leave the nest and search for a place with a more humid microclimate suitable for the growth of the cordyceps. When the ant reaches the ideal location for the fungus “housing,” the parasitic mushroom paralyzes the insect and slowly kills it. After that, a fruiting body of the fungus sprouts from the victim’s head, and new spores are released into the air in search of the next victim.

To see cordyceps in action, you can watch a fragment from David Attenborough’s Planet Earth, which once inspired the creators of The Last of Us game.

Why doesn’t cordyceps infect humans? Do we have immunity against it?

First of all, the nervous system of insects is not as complex as that of humans – that’s why it is easier for the cordyceps to take control of them. In addition, this parasite is not a match for the human immune system. Lastly, the human body temperature is too high for most fungi, including the cordyceps, to grow inside. Fungi generally prefer lower temperatures. That’s why fungal infections in humans usually develop on the skin, where it’s cooler. Some mycologists believe that humans and other animals have developed such a high body temperature precisely to protect themselves from fungi.

But what if mushrooms eventually overcome these barriers and “jump” onto humans?

This will take too much time. Parasites have adapted well to their hosts, learning to utilize their physiology and immune system, but the transition from one species to another is not so simple. Hosts and parasites engage in a kind of arms race – one develops defense mechanisms, while the other seeks workarounds. This is a very complex process from an evolutionary standpoint.

Parasitic fungi have developed alongside insects for millions of years and typically specialize in infecting a specific species. The specialized species of the Ophiocordyceps genus is responsible for infecting each individual ant species. The dangerous Cordyceps for one species of ants will not harm another.

Insects parasites are unable to “switch” to humans due to the incomparable time scale required to adapt to a new species. Fungi and insects are much older than humans. The age of the kingdom of fungi is estimated to be hundreds of millions of years, and some estimates suggest it may reach 2.4 billion years. Insects appeared approximately 480 million years ago. Parasitic fungi and their insect hosts had hundreds of millions of years to get used to each other. Modern humans, in turn, have only existed for about 200,000 years – one can say that cordyceps have not yet noticed our appearance.

It would take millions of years for one of the species of cordyceps to “settle in” inside a human and start controlling us. But it’s not a fact that by that time humanity won’t go extinct from something else or, for example, won’t leave the Earth.

So, does it mean that mushrooms have no effect on human behavior at all?

Although mushrooms cannot turn us into zombies, they can definitely affect mood and behavior. One group of mushrooms – yeast – causes fermentation of grapes and barley, converting sugars in them into ethanol. This property of yeast allows for the production of wine and beer, which can cause intoxication in people. And hallucinogenic mushrooms, in turn, contain psychedelic substances that increase activity in certain areas of the brain.

What will happen if you accidentally eat cordyceps?

Actually, people have been using cordyceps for centuries, and no one has turned into a zombie. Cordyceps is used in traditional Chinese medicine. It is believed to treat coughs, strengthen the immune system, and also increase potency. It should be noted that there is no convincing scientific evidence of the benefits of cordyceps for the body.

But does cordyceps turn ants into zombies literally?

It depends on how we define the term “zombie”. From the perspective of mass culture, zombies are undead. Ants infected with cordyceps are not dead – they continue to perform their life functions.
In fact, it is advantageous for the parasite to leave its victims alive as long as possible in order to increase the chances of spreading its spores. In the process, infected ants obey the host, losing their independence – and in this sense, they really resemble characters from horror movies.

Great, we’re not threatened by a zombie apocalypse yet. So, the main thing is just not to eat pale rotten stuff, right?

Unfortunately, this is not the only problem. Fungal infections, or mycoses, annually claim over 1.6 million lives, and approximately one billion people suffer from parasitic fungus infections of the skin, nails, and hair. For comparison: fungi kill approximately the same number of people as tuberculosis, and three times more than malaria.

Fungal infections often affect people who are already seriously ill, such as those with cancer, tuberculosis, COVID-19, and other diseases. For example, during the pandemic, India experienced an outbreak of black fungus infection, or mucormycosis. As a result, more than 4,300 people died, whose immune systems were weakened by drugs for the treatment of coronavirus.

The spread of infections is facilitated by the fact that pathogens develop resistance to antifungal drugs due to their excessive use in agriculture. The problem is exacerbated by the fact that historically less attention has been paid to the study of fungal pathogens than to viruses and bacteria.

From this point of view, is cordyceps dangerous?

No. Last year, the World Health Organization identified 19 fungal pathogens posing the greatest threat, and cordyceps was not among them. However, experts included in the “critical group” the most harmful fungi, such as drug-resistant Candida auris, responsible for outbreaks of infection in hospitals worldwide, and Aspergillus fumigatus, a mold that causes tumor-like formations in the lungs and sinuses. It’s not The Last of Us, of course, but it still looks unpleasant.

However, there is also good news: the majority of mushrooms are not harmful to humans – out of over 150,000 known species, only about 200 can infect a person.

And can global warming somehow affect Cordyceps and make it really dangerous for humans?

If it does happen in reality, it won’t happen soon. But other types of pathogenic fungi are becoming more common due to climate change and this creates problems for people right now.

Do you remember when we mentioned outbreaks of Candida auris in hospitals? It actually thrives in high temperatures, which means that it could become one of the beneficiaries of global warming. Additionally, it spreads from person to person, even though such behavior is not typical for parasitic fungi. Scientists discovered this fungus just over a decade ago, and outbreaks of infection caused by it have already occurred on several continents, possibly due to higher temperatures. Along with its resistance to antifungal drugs, all of this makes it as dangerous as the fictional cordyceps from the series.