The Cordyceps brain infection is central to the narrative and the storytelling on HBO's post-apocalyptic drama, The Last of Us. It breaks among the masses in the United States on Friday night, September 26, 2003, and two days later, everything is destroyed.

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The Last Of Us season 1, episode 1, "When You're Lost In The Darkness," opens with the Millers, Joel, Sarah, and Tommy listening to a vague news report about "...continued disturbances in Jakarta." The show doesn't immediately clear what this disturbance is, but come night, it's obvious that some sort of pandemic is underway. Twenty years later, the Cordyceps outbreak has ravaged humanity and turned humans into the infected. The Last of Us shows the infected (host) go through goes different developmental stages depending on how long they've been infected.

4 Runners

Nana is infected in The Last of Us.

Runners, as the name suggests, are intensely fast, sluggish attackers, and they tend to run in swarms. Tommy, Joel, and Sarah encounter Runners in The Last of Us premiere while making their way out of Austin, Texas. Runners are in the early stage of infection, quite aggressive but the least scary of all. The Millers' neighbor, Nana is the first Runner encountered in The Last of Us. The show subtly teases that the fungus got to her through the contaminated biscuits and sugary items she consumed.

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Twenty years later, Joel (Pedro Pascal) explains to his cargo, Ellie that the outbreak likely spread among the human population through contaminated basic ingredients like flour and sugar. There were certain brands that were sold all across the world and got the world population infected. On the actual night of the outbreak, Sarah walks into the Miller household and sees Danny Adler bitten on his shoulder. She moves forward to see Nana in the process of infecting her daughter, Connie. As soon as Nana spots Sarah, she rushes toward her in a vain attempt to bite her. Sarah quickly makes her way out of the Adler house, only to watch her dad, Joel kill Nana with a wrench a minute later.

3 Stalkers

Infected under debris in The Last of Us.

Stalkers are second in the developmental stage, and they are right behind Runners in terms of scariness. This stage arrives anywhere between two weeks after the host contracts the Cordyceps brain infection. Ellie encounters a Stalker in trapped debris right in the basement of the Cumberland Farms at the beginning of The Last of Us season 1, episode 3, "Long, Long Time." The infected has its eyes on Ellie the whole time, and it emits croaks as she approaches closer. It has tendrils growing through one of its eyes, and it still retains some of its human features. Ellie gives it a slash on the forehead and eventually stabs it to death with her folding pocket knife.

The infected can remain in the Stalker stage for over a year. They are much more methodical than Runners, in that, they can prefer to hide and attack humans, thus earning them the name Stalkers. They are also stronger than Runners and are known to attach themselves to walls with fungus gradually sprouting out of them.

2 Clickers

Joel aims at a Clicker in The Last of Us.

Stalkers shift into Clickers in the third stage of the Cordyceps brain infection. These types of infected are scarier than their preceding kind, and they are named Clickers because of the clicking noise they emit while searching for their prey. The fungal infection is prominent on their head, and it overtakes their eyes, thus rendering them blind. Unable to see, Clickers limp around their space and demonstrate the use of rudimentary echolocation to prey on humans and to communicate with their kind. Once they hear noises, they rush toward the source of the sound.

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Clickers' heads are badly deformed by the infection, and their skull is split in two to allow further fungal growth. At this stage, they only retain their mouth and teeth in order to bite the victims. Clickers are seen lurching through a museum in The Last of Us season 1, episode 2, "Infected." Unfortunately for Joel's smuggling partner, Tess, she gets bitten by one of the infected in the melee. Clickers are essentially more fungus than human and are much harder to kill.

1 Bloaters

A Bloater in HBO's The Last of Us.

Clickers turn into Bloaters several years after being infected with Cordyceps. Bloaters are entirely fungus, and scarier than Clickers. Their outer body is completely covered in thick fungal armor because of which they become incredibly hard to kill. The Infected develop into Bloaters in dry locations.

The Last of Us season 1, episode 5, "Endure and Survive," features an enormous Bloater that pops up from underground during the confrontation between Kansas City revolutionaries, led by Melanie Lynskey's Kathleen, and Henry and Sam. Because of the Bloater's fungal armor, it is able to withstand a barrage of bullets from Kathleen's right-hand man, Perry's assault rifle. It towers over humans, and lifts and smashes them to death. It runs towards Perry and tears his head off his body thereby terrifying those who witness the scene.

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