The Last of Us Fungal Infection Explained | MojoPlays

VOICE OVER: Dave Thibault WRITTEN BY: Johnny Reynolds
We've seen humanity fall to zombies countless times, but never quite like this. Welcome to MojoPlays, and today we'll be exploring the history and science behind the Cordyceps Brain Infection from “The Last of Us.”
The Last of Us Fungus Infection Explained
We’ve seen humanity fall to zombies countless times, but never quite like this. Welcome to MojoPlays, and today we’ll be exploring the history and science behind the Cordyceps Brain Infection from “The Last of Us.”

The fungal infection’s effects are similar to those in other zombie media. Once infected, the host loses all higher brain functions and lashes out animalistically. But this isn’t some biological weapon produced in a lab. Writer and co-director Neil Druckmann wanted the outbreak to seem realistic. And the inspiration the team used for their infection is pretty terrifying in its own right.

CBI is based on the real-life fungus Ophiocordyceps unilateralis, or Cordyceps for short. It’s predominantly found in tropical forests and infects small insects. After the release of “Uncharted 2,” the staff at Naughty Dog were searching for inspiration for their next IP. A clip from the BBC documentary “Planet Earth” is where they found their jumping off point.

There are different versions of Cordyceps for different insects, but the “Planet Earth” clip focused on one that afflicts ants. The fungus will infect a single ant, growing on the brain to control them. From there, it forces the ant to latch onto a nearby plant. After the ant dies, its infected corpse will produce spores, spreading the fungus to the colony. The higher population of an insect, the more likely it is to be targeted. Given that Earth is obviously well-populated with humans, Naughty Dog knew they had something special.

The fall of humanity began on September 26th, 2013. Also known as Outbreak Day, this is when the fungus reached critical mass and when the infected began to turn ugly. But it had been spreading for some time before then. According to a newspaper players can find in the opening chapter, the fungus began by infecting crops in South America. However, the FDA also warned against crops from Central America and Mexico. Unfortunately, it spreads extremely quickly. At least in Texas, hospital admittance increased by 300%. In a matter of months, around 60% of the world’s population had either died or become a creature of nightmares.

Once CBI has its host, it travels to the brain swiftly where it will grow and eventually control the host’s actions. Even when a host dies, the fungus continues to grow. Some infected will go into dark, dank places to produce infectious spores when they die. However, unlike the real Cordyceps, CBI makes the host behave violently in order to poison the healthy through bite. And since the fungus grows constantly over time, there are a variety of stages and physical changes the infected go through.
It takes less than 2 days for a completely normal person to turn into an enraged beast. The Federal Disaster Response Agency classifies Stage 1 infected as Runners. These will sprint towards their prey in large numbers to overwhelm them. Since the host has not been infected long, there aren’t many changes in their physical appearance other than bloody eyes and small warts on the neck and head.

Infected hosts progress to Stage 2 within a year. Classified as Stalkers, these monsters are usually a bit stealthier than Runners. With the Cordyceps fungus continuing to grow, it will protrude from the skull, partially blinding them. This also heightens their sense of sound, but the following stages are truly the most horrific.

After a year, hosts will enter Stage 3. Here, the fungus has grown to cover the entire top half of their head, blinding them completely. To adapt, the host will develop a form of echolocation. By making clicking sounds, the infected can determine the location of prey, thus giving them the popular branding of “Clickers”. This is also something taken from real life. Neil Druckmann was inspired by a news story about a blind boy using clicking sounds for the same result.

While in the real world it’s fascinating, in the game it’s absolutely frightening. In addition to advanced hearing, Clickers are also much stronger than the standard infected. If the player can’t put a Clicker down before it reaches them, it’ll rip their throat out. And that’s a lot easier said than done. The hardened fungal growths act as plates of armor which makes it a lot harder to land a headshot.

Stage 4, the “Bloater” is clearly the most troublesome, though thankfully rare. It takes more than a decade for an infected to become a Bloater. Here, the physical changes are at their most extreme. Fungal plates have grown over the entire body, causing the infected to grow larger and slower. The growths make them incredibly difficult to kill. Even though they’re much slower, Bloaters can rip fungal growths from their bodies and hurl them at prey. And just like with Clickers, they’ll kill you as soon as they touch you.

“The Last of Us” takes place with humanity on the brink of collapse. Less humans seem to be left at the end of every day. In the 20 years since Outbreak Day, no one has found a cure. Although, one could theoretically exist. Ellie is the only person shown to be immune to the fungi’s effects. While Firefly doctors planned to remove the fungus from her brain in order to produce a vaccine, we all know how that turned out.

“Part II” may explore the possibility of a cure again, but it will also show how the infection can adapt and mutate. A new class known as Shamblers is produced through a combination of exposure time and environmental factors. It’s similar in size to Bloaters, but it can spray infectious gas that will burn a victim’s skin and impair their vision.

CBI is one of the deadliest plagues to ever appear in video games. It’s basis in real-life science, it’s rapidity, and it’s ability to mutate hosts is what makes “The Last of Us” so uniquely terrifying. We’re excited to explore how this infection has grown and adapted in the sequel. But we’ll be infinitely grateful if the real Cordyceps never evolves past insects.