Eesha Kulkarni

HBO’s post-apocalyptic drama television series created by Craig Mazin and Neil Druckmann, The Last of Us, follows the story of a dreaded smuggler who is tasked with escorting a teenager across a post-apocalyptic world and is compelled to join hands with a young apprentice to fulfil the mission unscathed.

The video-game inspired series starts by introducing a terrifying infection, known as Cordyceps, which has all but destroyed human civilization as we know it. It’s a bleak and horrifying scenario, rife with quarantine zones and armed guards set up in the aftermath—and a resistance movement known as the Fireflies gearing up to face off against FEDRA (Federal Disaster Response Agency).

What exactly is the infection Cordyceps, and how does it work?

Here’s everything you need to know about the creepy infection in the show—filling in some blanks with details from the original games. The virus is a very real type of Cordyceps infection which infects ants and inspired the version seen in The Last of Us. So, for a deep dive into the Cordyceps brain infection, look no further than the below.

What is the Cordyceps brain infection in The Last of Us?

The Last of Us episode 1 begins with a terrifying discussion between an epidemiologist and a TV show host about an infectious disease. The expert explains that humanity has faced many types of illnesses over the decades but has always prevailed—and the type of infection that really scares him is of the fungal variety. He explains how some fungi can essentially turn hosts into brainless zombies, and lists a number of such fungi, including Cordyceps.

Luckily, though, fungi isn’t built to survive a human body’s internal temperature, so it’s not a realistic worry. So here’s hoping that rising temperatures don’t push human bodies into evolving to withstand higher temperatures, otherwise we’re doomed, right?

The series then flashes forward to 2003, as ominous signs play harbinger to the impending havoc. Everything quickly turns to chaos and multiple infected people are spotted chasing survivors and violently attacking them. When another time skip takes us into 2023, we learn that Cordyceps has obliterated civilization as we know it.

It’s clear that Cordyceps is exactly what the epidemiologist had predicted in the beginning of the show; a parasitical fungal infection in the brain that turns humans into zombified hosts, whose only goal is to spread their infection to as many other people as they can. The protagonist Joel’s elderly neighbour is seen infecting the people she lives with, and, in one terrifying moment, we see tendrils of the fungus appearing from her mouth.

In the game, the infected come to be called clickers, thanks to the disturbing sound they make. Ultimately, the infection does completely kill the host, as seen when Joel and Tess come across a gruesome dead body in the premiere.

What is Cordyceps’ origin and how does it spread?

The origin of the show’s Cordyceps pandemic hasn’t been revealed just yet but, in the game, infected crops are responsible for the infection spreading to humans.

In the show, infected wounds seem to be the only medium of spreading the illness so far, but in the game, airborne spores are also a threat—though co-creator Craig Mazin has explained that this won’t be the case in the series.

“The game had spores in the air and people had to wear gas masks, and we decided, early on, that we didn’t wanna do that for the show,” he shared. “Eventually, those conversations led us to these tendrils. And then, just thinking about how there’s a passage that happens from one infected to another, and like fungus does, it could become a network that is interconnected. It became very scary to think that they’re all working against us in this unified way, which was a concept that I really liked, that got developed in the show.”

Signs that a person is infected include an involuntary twitching, and by 2023, a quick scan can indicate if someone has Cordyceps or not.

So, is Cordyceps real?

Yes, Cordyceps is very much a real fungus. Luckily, though, it doesn’t turn anyone into a mindless zombie, it just preys on insects. Hundreds of species of Cordyceps exist, though The Last of Us’s version is inspired by Ophiocordyceps unilateralis, which, per expert David Hughes, who consulted on the first game, doesn’t actually infect the brains of the ants it targets, rather the rest of the body—though this wasn’t discovered until long after the game was released.

But, even though the infection doesn’t affect the brain, the fungus does manipulate its victim’s behaviour via the muscles. It compels the infected ant to travel somewhere up high, bite down on a leaf, then hang themselves to death. After the ant has died, the fungus grows a long stalk from its body and releases infectious spores that float down below. The deadly parasitic fungus is capable of wiping out entire colonies of ants. The idea for the Cordyceps brain infection is inspired by the docu-series Planet Earth, that tracks one unfortunate ant through every stage of its infection.