You’ve seen them. The twitching. That awful clicking sound that echoes in a tiled hallway. Most people playing Naughty Dog’s masterpiece just see the Last of Us infected as another hurdle to jump over—another head to pop with a brick or a shiv. But honestly? The deeper you look into how these creatures actually function, the more you realize that the "zombie" label doesn't even come close to covering it. It’s a parasitic tragedy.
Let's get one thing straight right away. These aren't undead. They aren't Romero's shuffling corpses or the sprinting ghouls from 28 Days Later. They are living, breathing human beings whose brains have been physically hijacked by a real-world fungal genus called Ophiocordyceps unilateralis. Well, a mutated version of it, anyway. Neil Druckmann and the team at Naughty Dog didn't just pull this out of thin air; they saw a BBC Planet Earth segment about ants and thought, "What if that happened to us?"
The Four Stages of the Last of Us Infected
Becoming one of the Last of Us infected isn't a quick transformation. It’s a slow, agonizing descent. It starts with the Runners. These are the people who just got bit or breathed in enough spores. They still look human. They still wear their clothes. But their eyes? Bloodshot and vacant. They scream when they run at you, and if you listen closely to the audio in the game, it sounds like they’re crying or gasping. It’s like the person is still in there, watching their body do things they can't control. It’s a loss of agency that’s way scarier than just dying.
Then comes the Stalker phase. This is where the fungus starts growing out of the head. It’s messy. Stalkers are the smartest of the bunch, which makes them the most annoying to fight. They won't just run at you. They hide. They wait for you to turn your back. If you’re playing The Last of Us Part II, you’ve probably felt that spike of adrenaline when one of these things peels itself off a wall. They literally fuse with the environment. It’s gross.
The Sound of a Clicker
We have to talk about the Clickers. By this point, the fungus has completely blinded the host. The skull has split open, replaced by calcified fungal plates. Because they can't see, they use echolocation. That click-click-click isn't just a spooky sound effect; it’s the fungus navigating the world. They’re stronger than Runners. They’re tougher. One bite and you’re done. There’s a reason they’ve become the face of the franchise. They represent the moment where the human is officially gone, replaced by a biological machine designed only to spread spores.
Bloaters, Shamblers, and the Shifting Biology
The longer an infected survives, the weirder things get. You’ve got the Bloaters. These are the tanks. They’ve been infected for years, and the fungus has grown into a thick, armored hide. They throw "mycelium bombs" that release toxins. It’s basically chemical warfare. In the first game, the Bloater in the high school gym is the first "oh crap" moment for a lot of players.
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But then Part II introduced Shamblers. These are a mutation caused by high-moisture environments—specifically the rainy, damp streets of Seattle. They don't bite as much as they just release clouds of acidic spores. It’s a perfect example of how the Last of Us infected adapt to their surroundings. The fungus isn't static. It’s evolving.
And then there's the Rat King.
Honestly, the Rat King is the stuff of nightmares. Found in the basement of the Seattle hospital, it’s a "super-organism." It’s multiple infected people who have been trapped in a single room for twenty years, fused together by the fungus into one massive, multi-limbed horror. It’s the ultimate expression of what Cordyceps wants: total biological unity. It’s not just an enemy; it’s a graveyard of people who never got to leave.
Why the Spore System Matters
In the games, spores are the primary way the infection spreads through the air. You see Joel or Ellie pull on a gas mask, and the world turns into a hazy, yellow nightmare. But did you notice the HBO show changed this? They swapped spores for "tendrils."
A lot of fans were upset, but from a purely scientific standpoint, it makes sense. If spores were as prevalent as they are in the game, the whole world would be infected in a week. Wind would carry them everywhere. The tendril system—where the Last of Us infected are connected by an underground fungal network—creates a different kind of horror. It’s a hive mind. You step on a mushroom in one street, and a hundred infected a mile away wake up. It’s a terrifying concept of connectivity.
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Whether it's spores or tendrils, the goal of the fungus is the same: reproduction. When an infected person dies, they don't just rot. They find a dark, damp corner, lay down, and let the fungus grow out of them like a vine. They become a "fruiting body." They spend their literal afterlife spreading the very thing that killed them.
Real World Parallels: Is This Actually Possible?
Scientists like Dr. Hughes, who actually studied Ophiocordyceps, have weighed in on this. In nature, the fungus targets the muscles of ants, not the brain. It leaves the brain intact so it can pilot the ant to a high point, kill it, and then burst out of its head to shower spores on the colony below.
Could it happen to humans?
Probably not. Our body temperature is too high. Fungi generally hate heat. This is actually a major plot point in the TV show’s prologue—the idea that as the world warms up, fungi might evolve to survive in warmer hosts. Like us. It’s a chilling thought because it’s grounded in a sliver of biological truth. We are seeing more fungal infections in the real world, like Candida auris, which are becoming resistant to drugs.
How to Handle Infected in Gameplay
If you’re playing the games, you need to change your mindset. Most players try to "action" their way through. Bad idea.
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- Stealth is everything. Especially with Clickers. If you don't have a shiv or a brick, you're better off just staying in the shadows.
- The environment is a tool. You can often lure infected into human enemies. It’s fun to watch a group of Hunters deal with a Clicker you let loose.
- Fire is your best friend. Fungi hate fire. Molotovs are the most effective way to clear a room of Stalkers or to soften up a Bloater.
- Don't waste ammo on Runners. If you have to take them out, use melee. Save the shotgun shells for the things that won't die from a pipe to the face.
The Tragedy of the Last of Us Infected
At the end of the day, the Last of Us infected are symbols of a world that moved on without us. Nature won. The fungus isn't "evil." It doesn't hate Joel or Ellie. It doesn't have a political agenda. It just wants to exist. It wants to grow.
The horror doesn't come from the jump scares. It comes from the realization that every Clicker you kill was once a person with a family, a job, and a favorite song. They are the physical manifestation of the world's collapse. When you look at the beautiful greenery growing over the ruins of Boston or Pittsburgh, you have to remember that the same "nature" is what’s eating the characters from the inside out.
Actionable Survival Steps for Players
If you want to master the encounters with the infected, start paying attention to the details. Watch the growth patterns on the walls; they tell you if spores are nearby. Listen to the pitch of the shrieks; a Runner’s scream is different from a Stalker’s hiss.
- Invest in the "Listen Mode" upgrades. It feels like cheating, but seeing silhouettes through walls is the only way to survive Grounded difficulty.
- Always carry a brick. Bricks are objectively better than bottles. You can hit an enemy three times with a brick in melee, or throw it to stun a Clicker for a quick kill.
- Check your corners. Stalkers in Part II don't show up on Listen Mode if they’re standing still. You have to use your actual eyes.
The Last of Us infected aren't going anywhere. Whether we get a Part III or another season of the show, these fungal nightmares will continue to evolve. The best thing you can do is learn how they move, how they think, and exactly how much fire it takes to stop them.