‘The Last Of Us’ Different Stages Of Cordyceps Brain Infection, Explained

The premise of HBO’s “The Last of Us,” adapted from the critically acclaimed video game of the same name, revolves around a post-apocalyptic world set two decades after a global pandemic triggered by a Cordyceps fungal infection decimates human civilization around the globe. The fungal infection presents a predicament worse than death. Akin to how real-life Cordyceps affect ants and bugs, in the game/series, the mutated Cordyceps fungus affects its host’s neurons, kills brain cells, and assumes control of the motor functions. After getting cognitive capabilities erased, the host turns rabid as the fungus modifies its only objective to spread the infection and thrives on its host’s body until death.


The unfortunate victims, known as “infected,” live out the rest of their remaining lives in a zombified existence. In its first two episodes, the series introduced viewers to variants of the infected, differentiated by the stages of infection, and these terrifying “living dead” ones constitute the primary hurdle for our protagonist duo, Joel and Ellie, in their quest for survival. The showrunners have managed to faithfully adhere to the game lore so far while adding some new changes that improve upon the source material, and the Infected ones are no exception. We will briefly discuss the inception of the infection, the different variants, and how they differ from the conventional zombified humanoids shown in fiction.

Spoilers Ahead


The Inception

In the prologue of the pilot episode of “The Last of Us,” we see in the year 1968 epidemiologist Doctor Neuman issuing an ominous warning for humankind in a talk show regarding a global outbreak of fungal infection. He opines that till then, the infection’s spread was constrained to smaller, simpler life forms like bugs, but in the near future, due to rising global temperature, the fungus mutating itself enough to make human beings their host is a strong possibility. In the year 2003, his apprehension comes true soon, as the prologue portion of the second episode shows that a flour mill in Jakarta becomes the ground zero of the infection, and as Mycologist Dr. Ibu Ratna remarks, flour makes the perfect substrate for the fungi. The viciousness of the infection can be understood by the fact that it took only a couple of days after the initial discovery to become a global outbreak. The spread through flour had significant foreshadowing in the first episode, as we see the surviving characters miss a bullet by not ingesting gluten or flour-based products. The ones who were not so lucky were turned into mind-controlled aggressive infected ones; their actions limited to spreading the infection to every last living human being. 

What Differentiates Infected From Other Zombified Humanoids?

Amidst the abundance of zombie-related content in live-action media, it is easy to confuse the infected ones with any random zombie terminology, and in a broader sense, they are encapsulated in the term “zombie,” but there are few differences that make the monstrosities of “The Last of Us” stand out. For starters, unlike conventional Zombies inspired from Haitian folklore, who are reanimated corpses, to begin with, the infected ones are very much alive human beings who have lost control over their neurological functions and intellect. They can be referred to as human beings who have turned rabid and feral after the Cordyceps takeover. This interpretation is closer to the entities in “28 Days Later,” “Left 4 Dead,” etc. Secondly, the source of inspiration behind the creation of the infected is based on real-world instances. As the game co-creator and creative director, Neil Druckmann, himself stated, they were inspired by the nature documentary “Planet Earth” after seeing instances of carpenter ants being zombified by the infestation of Ophiocordyceps.


Cordyceps use the infected ants like puppets, draining their nutrients completely. The fungus bursts out of the ant as a fruiting body, and by developing spores from the stationary, dead husk of the ant’s body, it infects the colony of ants. The infection in bugs worsens gradually, stage by stage, something which is also emulated in the lore. Appearance and activity-wise, the infected ones in the game and series were thus very similar to the given real-life instance. Even in the context of changing behavior patterns, a recent case study in a similar vein has shown instances on selected mammals – that Wolves in Yellowstone National Park are prone to be controlled by the protozoan parasites residing in Cougar’s feces which makes them act bolder and more courageous. The bottom line is that the biologically grounded and comparatively more plausible nature of the monster lore in “The Last of Us” gives it a distinctive edge.

Different Stages Of Infection

Depending on the severity of the infection through the varying time frame, the infected ones go through several stages in the game. Unlike the game, the stages are not explicitly mentioned by name in the series yet, but the production design made them instantly recognizable.


Runner: In the very first stage, the victims show clinical signs sometime after getting infected, which is often signaled by limb twitching, awkward movements, and loss of motor control. As the infection takes hold within a few hours or a day, depending upon the spot of the contamination, the victim starts acting extremely hostile and seeks to hunt down any living being. Once they get hold of a new host, they either transfer the fungal spore through tendril-like extensions in their mouth or kill them. In the first episode of the series, we see the elderly woman of the Adler family becoming the “runner,” and the reason can be speculated to be related to flour ingestion, which was the carrier substrate. The Runners are physically stronger than their host’s usual self, and as we see the elderly Adler running toward the Miller family at incredible speed after getting infected, perhaps the reason for the name is attributed to this behaviour. In the first episode, all the infected ones we see are ‘Runners.’

Stalker: After a couple of weeks into the infection, if the host survives, the fungus grows out of the human body, especially through the eyes or head, and gives a distinctive, gnarly appearance. As their name suggests, this group of infected stalk their prey and prefer to hide in dark places as a natural response to the fungus’ affinity to dark, cold places. Sometimes the stalkers attach themselves to walls or other look-alike structures and wait for their prey to arrive. One such instance is shown in the first episode when Tess and Joel encounter a body that had attached itself to the wall, but due to a lack of new prey, it drained the human body completely and formed mycelium inside the body, which got stuck and became a vicious sculpture of sorts. Stalkers prefer to stay in groups, and the way they spread the spores is by inserting tendrils through the mouth, which is shown in the second episode. They are tougher than the runners and lead their respective infected colonies.


Clicker: Ever since “The Last of Us” was rumored to be adapted into a live-action series, the fans of the game have waited expectantly to witness the design of Clickers, the iconic villain of the series, on screen. A year or more through the infection allows the fungus to change the morphology of its host as it grows into fungal bloom, splitting open the skull of the human inside. The major portion of the head up to the teeth gets covered in tough, scaly fungal protrusions. The eyes get consumed, and the host essentially becomes blind. To compensate for this, the host is forced to use echolocation using its vocal cords by creating “click” sounds; hence, the name. The human host at this stage is completely overtaken to the point where it has become a new creature of sorts, and it is much more aggressive toward any target it can shift focus on. Clickers are especially tough to kill as their speed is further complemented by their tough outer skin and strong armor-like layers on the head, which protect the brain. In the second episode of the series, we witness the encounter between our team of survivors, consisting of Joel, Ellie, and Tess, and two Clickers in the abandoned Bostonian Museum. Clickers gave a perfect chance to showcase the perfection of body horror excellence of the game, and the majorly prosthetic design served the purpose perfectly. 

Bloaters or Shamblers: Answering Ellie’s question about the lifespan of the infected, Joel remarks that some of them have been roaming the earth for twenty years. Bloaters are the kind of Infected whose infection took hold through several years and transformed the host’s entire physiology into some kind of fungal humanoid hybrid. In an environment with a wetter climate, Bloaters turn into Shamblers. This extremely strong and clumsy variant of Infected is almost entirely made of plate-like armor around its body, something that offers prolonged protection against any oncoming attacks. They can hurl toxin pouches or deadly spores by ripping portions out of their body, and Ellie’s mentioning about Super-Infected, who can throw explosive spores, was a reference to the Bloater. We have not seen a Bloater appear yet, but as the series trailer indicates, we will see one in action this.


Rat King: An extremely mutated mega organism consisting of multiple numbers of Bloater, Clicker, and Stalker is known as Rat King, something which references the natural chain connect model, which can sometimes be seen among rats. It can be assumed it happens after decades of fungal infection; the colony expands by fusing multiple stationary hosts into one. Although we are not sure whether we will witness this rare monstrosity, which is the toughest and strongest of the bunch, on-screen this season, the fungal mycelium-linked chain was shown in the second episode as the team sees from the hotel rooftop that a swarm of Infected are connected to a chain and are moving in unison – hinting at the presence of Rat King.     

Final Words

Veteran Production Designer John Paino and his team deserve praise for the beautiful sets they made for the series, which were practical and not CGI-based for the most parts, and the faithful rendering of Infected on screen was proof of the practical effects / prosthetic excellence, which made the scenarios very palpable. Thanks to them, the detailing of the appearance of Infected Stalkers and Clickers pop up in their gnarly glory and establishes a brutal reconnection with nature, which can be as beautiful as it can be terrifying. 


See more: What Does HBO Series Do Differently Than The Video-Game In ‘The Last Of Us’ Episode 1?

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Siddhartha Das
Siddhartha Das
An avid fan and voracious reader of comic book literature, Siddhartha thinks the ideals accentuated in the superhero genre should be taken as lessons in real life also. A sucker for everything horror and different art styles, Siddhartha likes to spend his time reading subjects. He's always eager to learn more about world fauna, history, geography, crime fiction, sports, and cultures. He also wishes to abolish human egocentrism, which can make the world a better place.

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