Could Global Warming Cause a Fungal Zombie Apocalypse?

Could a zombie fungus evolve like in The Last of Us?

If you haven’t seen or played The Last of Us, both the TV series and the games it’s based on are amazing, and I’d definitely recommend them. They’re based around a zombie apocalypse, but with a little bit more science compared to other examples of the genre. Most zombie films have pretty similarly vague origin stories, with a plague, or contagion, or virus originating in country X, and quickly spreading across the planet until only scavengers and brain-eating monsters are left. The Last of Us gives us a few more details about the nature of its plague though, and unlike most counterparts, it’s a fungal infection.

The opening scene brings up the mind-altering capabilities of compounds found in several fungi species, highlighting in particular Ophiocordyceps unilateralis; a parasitic fungus of the Ophiocoryceps genus able to control the behaviour of ants. The scene then goes on to propose that, while humans have largely avoided widespread fungal infection due to our warmer body temperatures, rising global temperatures could prompt species like this to evolve heat resistance and begin infecting us too. Unfortunately, while the Last of Us certainly takes this to the extreme, this scenario isn’t entirely as wild as it might seem. But exactly how possible is it?  

We can break this into two parts:

1. Could climate change give rise to a new deadly fungus, capable of infecting humans?
2. Could a fungal disease evolve which can turn humans into mindless zombies?  

Let’s start with the first.

Could climate change give rise to a new deadly fungus, capable of infecting humans?

Pretty terrifyingly the answer to the first of these isn’t only yes, but it already has. The fungus Candida auris (C. auris) was completely unknown prior to 2009 (although a sample from 1996 was retroactively identified as C. auris after its discovery). Shortly after, it was discovered to have emerged seemingly independently on three continents, and has since spread across much of the world, including the majority of North America, South America, Europe, Asia and Australasia, and many countries in Africa have also reported infections. This emergence and spread isn’t a completely solved mystery, but is generally agreed to be the result of an pre-existing species adapting for increased heat resistance in the face of rising temperatures.

Fortunately, like most fungi, C. auris infections are mainly opportunistic, in that they mostly occur in those with weakened immune systems or other infections, often in hospitals. But there’s no reason a more deadly fungus couldn’t similarly evolve better heat immunity.

Other examples of fungi that seem to have emerged as a result of climate change include wheat and barley pathogen Fusarium graminearum, which has replaced the less aggressive and less heat resistant Fusarium culmorum in many regions, and Batrachochytrium dendrobatidis, which infects amphibians. This fungus has now spread across all continents besides Antarctica and is responsible for one of the greatest pathogen-caused losses of biodiversity in history, driving the extinction and dramatic decline of about 200 species.

What makes this even scarier is we currently have very few antifungals to treat fungal infections. You’ve likely heard of antibiotic resistance: overuse of antibiotics quickly causing the evolution of dangerous bacteria, immune to the drugs used to kill them. Antifungal resistance gets far less press because at the moment it’s much less of a problem, with far fewer fungi capable of infecting humans, and those that can rarely being dangerous except to those with increased vulnerability (e.g. people with weakened immune systems). However, if more fungi capable of causing real harm to humans were to emerge, it would take far less for them to become resistant to our small repertoire of drugs, and we may find ourselves facing untreatable diseases.

So you can add fungal pandemic to the list of potential disasters that come with global warming.

Could a fungal disease evolve which can turn humans into mindless zombies?

Theoretically, but it’s pretty unlikely. A fungus would have to evolve in precisely the right way to induce any sort of specific behaviour in humans, and it’d far more likely to just kill you or cause some form of brain damage. Even the existing zombie ant Ophiocordyceps unilateralis fungus primarily targets a single species, although other species can be infected and manipulated to a lesser extent.

Having said that, there are several examples of fungi that influence host behaviour more subtly, like the rat-infecting Toxoplasma gondii, which reduces rodent’s fear of cats and makes them more likely to be eaten, so the fungus can reproduce in the cat’s gut. More worryingly, Toxoplasma infections in humans have also been associated with schizophrenia and other behavioural changes, possibly by increasing dopamine production in affected brain cells. This suggests that while unlikely, a fungus evolving to influence human behaviour more dramatically isn’t as wild a notion as you might think.

Despite all this, while evolution has been seen on surprisingly short timescales in some species, it generally takes thousands or even millions of years for more complex changes in an organism’s function to arise. A fungus rapidly and almost simultaneously evolving mind-altering abilities and the heat resistance needed to infect humans is pretty unlikely, and that’s without talking about numerous other things that are required for a fungus to be an effective pathogen and successfully survive the human immune system.

So to answer the question, ‘Could global warming really cause a fungal zombie apocalypse?’ - it might be more possible than you’d have thought, but it’s extremely unlikely. Let’s maybe just focus on all the other climate change disasters first :)