‘The Last of Us’: Everything to Know About the Fungus That Transforms People Into Zombies

These shrooms are definitely not to be experimented with


There’s a fungus among us — and it’s taking over.

HBO’s “The Last of Us,” like the video game it’s based on, takes place in a world ravaged by a fungus that kills whoever it infects — but not before turning them into apparently mindless, zombie-like monsters driven to attack anyone who remains uninfected. 20 years after the outbreak, at least in America the only remnants of civilization are brutally oppressive “Quarantine Zones” run by FEDRA, a fictional organization that appears to be all that’s left of the U.S. government, and scattered survivor settlements.

What is the fungus and what are its effects? Where did the outbreak start? How did it spread so fast that the world was overwhelmed? Is there a cure? After each episode of “The Last of Us,” we’ll add what we know. Warning, there are spoilers ahead.

What Is it?

via Wikipedia

The fungus, referred to in the show only as “cordyceps,” is a fictional, mutated form of the real-life Ophiocordyceps unilateralis, a fungal infection found in tropical locations that has the unfortunately apt nickname “zombie ant fungus.”

O. unilateralis slowly hijacks an ant’s motor functions until the ant is compelled to leave its nest and seek a location nearby that is more favorable to the growth of the fungus. This usually means crawling down a plant to a point 10 inches off the ground, where humidity is higher than in the nest, at which point the ant clamps its mandibles on the stem or on a leaf and remains there until it dies.

And of course, the dying part is horrible. The affected ant’s internal organs are slowly consumed as fungus grows, with death coming 4 to 6 days in. At that point, a fruiting body explodes out of the base of the ant’s head, releasing spores that infect other ants. Of course, unlike on “The Last of Us,” infectees don’t suddenly start attacking other ants, but they are forced to behave in ways that guarantee the fungus is able to reproduce and spread.

Horrifyingly, during the first few days the ant displays no symptoms, which means it isn’t kicked out of the nest as is normally the case with sick ants. Even worse, scientists have found that the fungus never actually infects the ant’s brain. Imagine then being infected with something that robs you of any control over your body — while being aware of every agonizing moment.

And yes, infection is 100% fatal.

How Did It Infect Humans?

In real life, fungi in the genus Ophiocordyceps (roughly translated, it means snake-like club-headed) only infect insects. So what changed? The prologue of the first episode of “The Last of Us” has the answer.

It opens with the broadcast of a late 1960s chat show (modeled after the “Dick Cavett Show”) where learned guests are discussing potential risks to the survival of the human race. One of the guests, a scientist named Neumann (John Hannah) dismisses the suggestion that viruses or bacteria are the bigger threat.

“Mankind has been at war with the virus from the start. Sometimes millions of people die as in an actual war, but in the end, we always win,” Neumann says, arguing instead that we should be worried about fungi.

“Fungi seem harmless enough. Many species know otherwise, because there are some fungi who seek not to kill, but to control … Viruses can make us ill but fungi can alter our very minds,” Neumann continues, specifically referencing O. Unilateralis.

The show’s other guest points out that human bodies are too warm for such fungi to survive.

“True, fungi cannot survive if its host’s internal temperature is over 94 degrees. Currently, there are no reasons for fungi to evolve to withstand higher temperatures,” Neumann replies. “But what if that were to change? What if, for instance, the world were to get slightly warmer? Now there is reason to evolve. One gene mutates…and any one of them could become capable of burrowing into our brains and taking control not of millions of us but billions of us. Billions of puppets with poisoned minds permanently fixed on one unifying goal: to spread the infection to every last human alive by any means necessary.”

In short, global warming created the necessary conditions for O. Unilateralis to mutate into a form that can infect humans. And in the alternate history timeline of “The Last of Us,” that ended up happening in 2003.

How Does the Infection Spread?

Nana after being infected. (Photo credit: HBO)

In the original video game the infection spread via spores, just like the real-life version. That posed visual problems for live-action television — Actors’ faces would have to be constantly covered with masks to maintain any realism. So on the TV series, cordyceps are spread via ingestion.

The most common means portrayed on the show is fluid-to-fluid contact: Infected humans transmit it by biting their victims, or via a unique form of Mycelium (threads common in fungal colonies) that present as disgusting tendrils emerging from their mouths.

But that’s not the only way.

In Episode 3, it’s revealed that the prevailing theory among survivors is that the fungus was helped by the (then-still new) globalized marketplace. Foodstuffs like bread or grains that were manufactured wherever the initial vector was, the theory goes, somehow became tainted by the fungus. Then, sold all over the world, these goods would have arrived in stores around the same time, at least within countries, and thus would have been sold, and subsequently consumed, around the same time.

About that…

When Did ‘The Last of Us’ Fungus Outbreak Start?

As seen in the first episode, civilization collapsed on Sept. 26, 2003. In Austin, Texas, Sarah Miller (Nico Parker) and her father, Joel (Pedro Pascal) are planning to celebrate Joel’s 36th birthday with a pancake breakfast. That is, until Joel’s younger brother Tommy (Gabriel Luna) shows up to remind them they have a big job that day. Joel skips breakfast and leaves with Tommy, and Sarah never ends up making the pancakes.

Sarah goes about her day normally but as time passes we get glimpses of growing chaos all over the world. Accounts of local violence, a massive increase in police activity, and news reports of chaos in several cities around the world — including Jakarta, the capital of Indonesia. By the end of the day, Austin is overrun by infected humans, the military has resorted to summarily executing anyone who looks even slightly off, and Sarah is killed while she, Joel and Tommy are trying to escape.

20 years later (2023), we learn Joel and Tommy are still alive, with Joel in the Boston Quarantine Zone (QZ).

Episode 2 reveals the likely origin of the outbreak. On September 24, 2003, Indonesian military police enlist Dr. Ibu Ratna, Professor of Mycology at the University of Indonesia, to conduct an autopsy on a local woman.

To her horror, Ratna confirms the woman was infected with cordyceps, something that shouldn’t have been possible. The commanding officer explains that the woman worked at a factory that manufactures grain flour, which Ratna calls “a perfect substrate” — the optimum place for the fungus to grow. It seems that just over a day earlier, the deceased woman suddenly became violent and attacked three coworkers. All four were killed, the fungus was discovered, but whoever bit her was still loose, and now 14 workers are unaccounted for.

Ratna tells government officials that they need to bomb Jakarta to rubble and kill everyone in it if they want to stop the spread of the diseases. But as we saw in the previous episode, she was too late. The implication seems to be that the fungus got into the grain much earlier and had already been shipped worldwide. But hey, good thing Joel decided to skip that pancake breakfast.

How Quickly Does the Infection Spread?

The speed at which someone succumbs to the infection depends on how they were infected. A poster seen in the Boston QZ in 2023 for instance breaks down how it depends on where someone was bitten by another infected:

  • Neck, face, head — 5-15 minutes until full infection
  • Torso, arm, shoulder, hand — 2-8 hours
  • Leg, foot — 12-14 hours

What Does the Infection Do?

A man whose body has been consumed by the fungus. (Photo credit: HBO)

The infection takes over a person’s cognitive functions, turning them into mindless, flesh-craving zombies. It also takes over their motor functions. In the case of Nana — who was wheelchair bound — the infection restored her ability to walk and even run.

In 2023, Joel and Tess stumble upon the body of a man whose body has exploded after being infected with the fungus now growing on the wall.

In Episode 2, Tess explains the fungus can spread over a vast area, serving as a network for the cordyceps. Movement in one area can be detected up to a mile away. The survivors discover this the hard way after killing one Infected in the state hall alerts the other infected in the Boston area.

However, it does appear the fungus can be “burnt out” or be rendered inert in some areas as well.

What Types of Infected Are There in “The Last of Us”?

People who are recently infected, like Nana, are referred to as “runners.” Per their name, they tend to rush toward their prey.

Episode 2 introduces “clickers.” These are people who have been infected for over a year and the fungus has grown over their heads, rendering them blind. They still can hear very well and are super strong. Joel, Ellie and Tess fight off two “clickers” in the Boston museum.

Episode 5 introduces “bloaters,” people who have been infected for years. The fungus has hardened to essentially form a suit of armor around an infected’s body. The bloaters are also superhumanly durable and strong, and able to literally tear their victims in half.

Is the Infection Detectable?

By 2023, mankind has developed the ability to detect cordyceps.

A boy who stumbles into the Boston quarantine zone is scanned with a handheld device. His scan turns red, showing he is infected. Later, Joel disposes of the boy’s body in an incinerator.

A poster on the wall outlines the symptoms of cordyceps infection: coughing, slurred speech, muscle spasms and mood change.

At the end of Episode 1, the FEDRA soldier Lee scans Joel, Tess and Ellie. Joel and Tess’s scans are green, but Ellie’s scan is red.

In Episode 6, the survivors in Jackson, Wyoming use specially trained dogs to sniff out if someone is infected.

Is There a Cure?

As of now, there doesn’t appear to be a cure for infection.

In Jakarta, when asked about a cure, Professor Ratna answers, “There is no medicine. There is no vaccine.” Her only recommendation? Bombing the city and everyone in it.

In Episode 2, it was revealed that Boston and other major metropolitans were bombed, which only slowed the infection temporarily.

Ellie has survived despite claiming to have been bitten three weeks prior, so there may be something unique about her physiology preventing her from being infected.

Otherwise, according to the poster, she should’ve been fully infected within 2 to 8 hours.

Ellie is confirmed to be immune when she is bitten again in Episode 2 and does not turn.

In Episode 5, she cuts her hand and rubs her blood on Sam’s leg, which was bitten by an Infected as they were fleeing Kansas City. Unfortunately, it has no effect, and he turns in the morning.