How did The Last of Us outbreak start? Cordyceps explained

An image of Joel and Ellie in HBOs The Last of Us, played by Pedro Pascal and Bella Ramsey.HBO

The Last of Us is set in a post-apocalyptic world that has become overrun by various types of dangerous infected but what caused the initial outbreak in the HBO show? Here’s everything you need to know about the outbreak in The Last of Us.

The Last of Us has become one of the most celebrated video games of the 2010s due to its emotional character-driven narrative, and the beloved story is about to be shared with a wider audience in the form of the upcoming big-budget HBO show.

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The original game follows Joel and Ellie as they journey across a virus-ridden post-apocalyptic America, facing many dangers including the perilous infected – humans taken over by a virus that results in them becoming blood-craving monsters – but what initially caused the outbreak that created the infected?

Here’s everything you need to know about the outbreak in HBO’s The Last of Us.


What caused the outbreak in The Last of Us?

An image of Joel and Ellie in The Last of Us HBO show hiding from an infected clicker.HBO
The outbreak that created the infected in The Last of Us was caused by a Cordyceps brain infection.

In the show, the outbreak that devastated the world was caused by the Cordyceps brain infection (CBI) – an infection born from a mutated strain of Cordyceps fungus that develops on the brain. This is exactly the same as the game.

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The parasitic fungus begins to grow while the host is still alive and mutates multiple times causing various stages of infection – the first of which is the loss of higher brain function which irradicates a person’s sense of rational thought and renders them hyper-aggressive.

CBI can be spread via exposure to airborne spores or being bitten by an infected. Once a person has been infected the first symptoms of the virus take effect within a couple of days.

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Stages of infection

An image of a Bloater from HBOs The Last of Us.HBO
There are various mutations of infected in The Last of Us.

Those infected with Cordyceps may notice symptoms such as coughing, slurred speech, muscle spasms, and mood changes. The infection takes just 5-15 minutes to take over one’s neck and head, 2-8 hours for the torso and arms, and 12-24 hours for the legs and feet.

The Cordyceps fungus infection continues to mutate over time once a person has been infected which results in multiple kinds of infected.

In the original game, there are four distinct stages of infection – from the still human-like Runners and stealthy Stalkers to the iconic Clickers and imposing Bloaters, each mutation has unique qualities depending on how much the fungus has spread around the body.

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If you want to know more about the different mutations, you can read all about them right here.

What is The Last of Us outbreak based on?

The CBI in the game was inspired by and based on a real infection that according to an Inverse article, specifically affects carpenter ants.

The fungal parasite known as Ophiocordyceps unilaterali grows inside the ants and takes them over in much the same way that the Cordyceps infection affects humans in The Last of Us.

This is also explained by Dr Newman (John Hannah) in the prologue of Episode 1. He says a viral pandemic doesn’t keep him up at night, because we “always win.”

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But what if our bodies evolved with the changing heat of the planet, allowing fungus the sustenance it requires to live in our bodies indefinitely? What if infections limited to ants could affect humans, with the fungus growing into our brains, filling them with hallucinogens, and devouring its host – all while keeping them alive to spread to “billions of puppets”, without any conceivable treatment?

This is the nightmare Dr Newman envisions, and he’s asked what would happen if such terror ever came to pass. “We lose,” he says, capping off the show’s chilling opening.

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When did the outbreak happen in The Last of Us?

The official date of the outbreak in the show was September 26, 2003, which was the day the Cordyceps infection reached critical mass and led to humanity’s eventual downfall.

This meant that the core events of the game took place in 2033, however, it has been rumored that the timeline of the HBO show will be adjusted by 10 years – meaning the main story would take place in 2023 with the initial outbreak happening in 2003.

Until the show airs, however, there’s no official confirmation as to whether the timeline will be changed.

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The Last of Us Episodes 1 & 2 are available to stream now.

For more TLOU content, check out some of our below guides:

Joel & Tess explained | Sarah spoilers | Fungus threat is terrifying | The dog’s fate | Who is Marlene? | Why is Ellie so important? | Soundtrack choice | FEDRA & the Fireflies explained

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