A global disease outbreak is on everyone’s mind right now – and not just because of the Covid-19 pandemic.
The last of us The TV show, based on the popular video game, debuted this month on HBO, and the deadly pandemic is teased in the show’s opening moments. Two scientists debate whether a fungus or a virus is more likely to cause a pandemic.
(Spoilers ahead for The last of us!)
“Viruses can make us sick, but fungi can change our minds,” explains one researcher, arguing that the right fungus can create “billions of puppets with poisoned minds, permanently fixated on one unifying goal: to spread the infection to every human being alive. by any means necessary.”
Cut to later in the show and we learn that the cordyceps fungus has caused a deadly global pandemic that few have survived twenty years after the initial outbreak. The fungus appears to affect the brain, manipulating the human body to attack, eat and infect others.
But is it really fungi we need to fear – not viruses – when it comes to disease outbreaks? Although that question is debatable, there is one thing scientists are clear about.
“There is no infectious agent that turns you into a zombie,” says William Schaffner, professor of infectious diseases at Vanderbilt University. Reverse. But that is not the case for all living things…
Reel Science is a Reverse series that reveals the real (and fake) science behind your favorite movies and TV shows.
What is the cordyceps fungus and can it infect humans?
ONE National Geographic video shows how a parasitic fungus can manipulate ant behavior.
The show portrays the cordyceps mushroom as the source of the global zombie outbreak. It turns out: this fictional depiction actually originates from a real parasitic fungus known as Ophiocordyceps.
“Ophiocordyceps is a genus of behavior-manipulating fungi closely related to Cordyceps mushroom starring in the new HBO series The last of us,” William C. Beckerson, a postdoctoral fellow who studies Ophiocordyceps at the University of Utrecht, says Reverse.
The fungus is widely used as a traditional Chinese medicinal supplement for its supposed anti-inflammatory properties, but it also has a more sinister reputation for its parasitic ability to infect and manipulate ants’ behavior through its spores. It falls into a category of fungal parasites known as “entomopathogens” that turn insects into zombie-like creatures.
“Many of these ‘zombie-creating’ entomopathogens cause their hosts to show increased activity, seek elevated positions, and display body postures that promote spore dispersal,” the authors of a 2021 paper published in mBio.
“Fungi can clearly cause human diseases”
So: if the fungus can infect and manipulate ants, can it do the same for humans?
“When it comes to infection, one of the biggest barriers for fungi that Ophiocordyceps is the difference in body temperature between us and their usual insect hosts, says Beckerson.
Humans are endothermic, meaning we have an internally regulated body temperature that hovers around 98.6 degrees Fahrenheit. Ants, on the other hand, are exothermic, meaning their body temperature depends on the external environment. Therefore like mushrooms Ophiocordyceps evolved to infect ants when the temperature is between 60 degrees Fahrenheit (16 degrees Celsius) and 75 degrees Fahrenheit (24 degrees Celsius). So this specific fungus is unlikely to infect a human.
“However, this does not mean that any of the compounds made of Ophiocordyceps could not affect people, says Beckerson.
Beckerson is currently studying a molecule made of Ophiocordyceps — similar to the plant pathogenic fungus Aspergillus mentioned briefly in the show – which causes tremors in cows eating fungus-infected grain fodder. He hopes such research will one day lead to researchers developing better therapeutic drugs for behavioral disorders.
“This is at least one example of a chemical that can affect both insects and mammals and highlights the value of scientific research on these fascinating fungi,” adds Beckerson.
Is the show’s depiction of the cordyceps mushroom realistic?
In the opening scene of the show, a scientist in the 1960s states that fungi cannot survive if the host’s internal temperature is above 94 degrees Fahrenheit. But the researcher goes on to suggest that fungi could evolve to withstand higher host body temperatures – like in humans – in a slightly warmer world.
Cut to decades later and we are actually living in a slightly warmer world due to climate change.
“I was very impressed with the scientific accuracy of this opening scene. One of the indirect consequences of global warming is actually the emergence of new fungal pathogens,” says Beckerson.
Beckerson explains that as environmental temperatures rise closer to 98.6 degrees Fahrenheit—the body temperature of humans—humans become a more likely host candidate for fungal pathogens. He says that microorganisms such as fungi are “particularly good at adapting to rising temperatures, and at a strikingly fast pace.”
“As the planet continues to warm, we will see more and more cases of fungal infections,” says Beckerson.
But even in a hypothetical scenario where a cordyceps pathogen from a zombie fungus – the same one that infects ants – could infect humans in a warmer world, it would still be difficult for the fungus to turn us into mindless zombies. Most zombie ants are infected by a particular Ophiocordyceps fungi that are unable to infect other ant species. Beckerson explains:
If you consider how these fungi are unable to manipulate organisms with very similar biology and behavior … it becomes clear that it would be extremely unlikely that – even in the event that humans were infected by such a fungus – that it would be able to manipulate our behavior in the ways depicted in The last of us.
Could fungi cause a global disease outbreak?
Fungi can infect humans and have done so for millennia. Athlete’s foot infections and vaginal yeast infections are common types of fungal infections.
“Fungi can clearly cause human diseases,” says Schaffner, an infectious disease expert at Vanderbilt University.
Nevertheless, he does not necessarily agree with the researcher The last of us that a fungus can cause a global pandemic. The main reason: fungi – especially those that cause serious illness – are not easily transmitted from person to person.
“You have to make something that fungi currently absolutely don’t know how to do, which is transferred quite quickly,” says Schaffner.
But Schaffner says there’s one fungus that’s causing serious outbreaks in hospitals around the world — though it’s unlikely to explode into a full-scale pandemic. That mushroom is called Candida auris, which the CDC says “presents a serious global health risk.”
Some sick individuals in hospital take antibiotics that suppress bacteria in the body, making them vulnerable to drug-resistant ones Candida auris, Schaffner explains.
“It’s long been thought to be a benign fungus, but it’s suddenly more than one place around the world. How did this happen? It’s still unknown and a big mystery,” says Schaffner.
So while it’s unlikely we’ll turn into flesh-eating zombies any time soon, The last of us offers a timely reminder not to overlook the very real threat fungi can pose to the world.
The last of us currently streaming on HBO Max.