HBO’s The Last of US has popularized one of the many spectacular ways in which mankind could go almost extinct. This time, it’s not a meteorite or a virus, it’s a deadly fungal transmission occurring on a large scale. While you may be only familiar with edible fungi, the WHO has recently released a whole list of deadly mushrooms that could bring you to your knees. However, the real question is — can any of these fungi turn us into zombies?

The Last of Us show is based on a video game of the same name featuring a fungal species called Cordyceps. The creators of the game did some good research because Cordyceps exists for real and it does have the power to make ants behave like zombies. However, what happens in the game and the TV show is that these fungi become evolved enough to infect humans as well, causing a Cordyceps-driven zombie pandemic.

A reality check on The Last of Us fungal outbreak

A 2020 study reveals that pathogenic fungal species kill over 1.5 million people every year, making fungi one of the most underrated yet deadly sources of infections that affect humans. However, if we only take into account the risk from Cordyceps, the chances of a fungal pandemic like the one depicted in The Last of Us are highly unlikely. The internal environment of the human body is not suitable for the survival and growth of Cordyceps.

The reason why Cordyceps infects only insects and particularly ants is that their bodies are naturally at low temperatures, their immune systems are weak, and their brains are not as complex as those of humans. The fungi leave their spores on the land, and as an ant comes into contact with the spores, the fungal cells make their way into its body. The cells thrive inside the hospitable environment of the ant’s brain and muscles and start releasing chemicals to alter the host’s behavior. 

The fungi keep eating the ant from inside and there comes a time when the fungal cells occupy about 50 percent of the host’s body mass. This is when the zombie behavior of the infected can be easily observed. The poor insect being controlled by the fungi leaves its own nest and starts moving towards another plant.  The ant moves as if it is heavily intoxicated and mindlessly climbs this new plant. When it reaches the desired height, it bites into the major vein of a leaf and then dies.  The spores of the fungi finally burst out of its head.  

Even if cordyceps-controlled ants bite a human, the fungal cells won’t be able to survive the high body temperature of the human body. Plus, there seems no way the fungi could survive our body’s complex immune responses. Another popular argument is — can Cordyceps evolve in a way that it learns to survive the human body? Well, according to biologists, it took Cordyceps millions of years to master their control over ants. So to infect much more complex human bodies, they’d have to evolve in an unbelievable way which seems unlikely.

“Our body temperature is simply too high for most fungi to nicely settle and grow – and this is the same for this Cordyceps. Their nervous system is simpler than ours, so it would definitely be easier to hijack the brain of an insect versus our brain, also their immune systems are very different from ours. For this fungus to be able to jump from an insect to us and cause an infection is a very big leap,” Dr. A.M. (Charissa) de Bekker, assistant Professor and biologist at Utrecht University told BBC.

However, Cordyceps is not the only threat. There are numerous fungal species that may not turn us into zombies but can cause inflammation in various parts of the human body and can even alter human behavior. For instance, studies show that exposure to Psilocybin mushrooms popularly referred to as magic mushrooms can change the mood of a person. They have both medicinal and hallucinogenic properties.

Whereas other fungal species like Cryptococcus neoformans and Histolasma can infect the lungs and cause diseases such as meningitis and pneumonia. The WHO list highlights several other species that can lead to a dangerous fungal outbreak. 

Reality is changing fast with the climate

Fungal infections have stayed limited to particular areas and geographies because fungi require a specific type of environment to grow and thrive. However, many experts believe that climate change could change this, and it’s already doing it. In a study published in the journal PLoS Pathogens in the year 2021, a team of researchers note:

“Climate change alters attributes of the fungus, the environment, and the host, which can then drive the emergence of novel, uncommon, or adapted fungal species, with consequences for health, biodiversity, and food security.” 

Another 2022 study published in the journal Annals of Internal Medicine claims that fungal infections are likely to become more common and widespread in the near future. They argue that due to the fast changing environmental conditions across the globe, many pathogenic fungi are now able to inhabit areas where they couldn’t survive previously. During their research also, they found that 10 percent of pathogenic fungi are now spreading in areas outside of their previously known geographical boundaries.

“We’re definitely seeing disease in locations that we previously have not and that’s concerning, because if we’re recognizing those locations, where are the places it’s occurring that just have not been recognized quite yet?” said George Thompson, first author of the 2022 study in an interview with NBC News. 

The rising global temperatures, disturbed rainfall patterns, and decreased immunity resulting from diseases like COVID-19 and cancer are increasing the risk of deadly fungal infections among humans.  

We can’t afford to underestimate fungal pathogens

Unlike bacteria and viruses, fungi don’t have a bad reputation among the masses. Most people know fungi only either as edible mushrooms or as the yeast which allows them to make bread and cheese. However, what they don’t know is there are numerous pathogenic forms of fungi as well. According to a report from Global Action for Fungal infections (GAFFI), more people die from such deadly fungal diseases than TB or malaria.

While there are many super-effective antibiotics and vaccines available to curb different kinds of bacterial and viral infections. There exist either fewer or no treatment options when it comes to many diseases caused by fungi. Interestingly, one of the main factors that contributed to the fats and uncontrollable spread of Cordyceps infection in The Last of Us was that there was no vaccine available. Well, you’d be surprised to know that in the real world also, we don’t have any vaccines to protect us from fungal infections.

Of course, there are some anti-fungal medicines but they are not equally effective against all kinds of fungal infections. What makes the situation worse is that some of the previously identified pathogenic fungi such as Aspergillus fumigatus and Candida auris have even developed resistance against antimicrobial drugs, according to the WHO deadly fungi list.

“Fungal diseases have become increasingly problematic. We have seen major issues with secondary respiratory mold infections in the context of the COVID pandemic leading to greatly increased mortality, and because we have witnessed the emergence of new outbreaks of antifungal drug resistance, with Candida auris and Aspergillus fumigatus a particular concern. In addition, it is notable that fungal disease is generally underappreciated by the wider public, for instance in the HIV-AIDS pandemic, it is not widely known that fungi were in fact the major cause of death as opportunistic infections,” said Darius Armstrong James, Director at Imperial College London’s Fungal Science Network.

In reality, the possibility of a fungus-driven zombie pandemic like the one seen in The Last of Us is highly unlikely (for now); but we can’t rule it out entirely. Especially with our constant tampering with nature, we cannot and should not ignore the risk of a deadly fungus outbreak because the truth is that we are not prepared for it. 

“I think we underestimate fungal infections at our peril. We’ve already done that for too long and we are completely unprepared for dealing with a fungal pandemic,” Dr. Neil Stone, an expert on fungal diseases told BBC.

We need more awareness, research, and treatment options to prevent the spread of any such infections because the one thing that COVID made pretty much clear to the entire human species is that — never underestimate the power of a tiny microbe.