An epidemic of a parasitic fungus infection that turns people into zombie-like monsters sets the stage for the events of the The Last of Us video game series.

The Cordyceps fungus normally only affects ants and other insects, but in the setting of The Last of Us, it has evolved to affect human hosts as well, leading to an untreatable brain illness.

The prologue of the game's newspaper reveals that the outbreak in The Last of Us was primarily caused by fungus-infected crops.

Just enough Cordyceps was present in the food to infect people, and once infected, the fungus almost drove the sick individuals insane. But there are other ways to become ill except by consuming cordyceps.

The disease can be transmitted through bites, like in most zombie tales, but it can also be contracted through close contact with Cordyceps spores.

You know, this fungus wants to spread itself as widely as it can in every situation.

Real-world In order to use the dead ants' bodies as fuel to grow and release more of its spores into the air to restart the cycle, the fungus Cordyceps will infect them, take over their motor functions, and cause them to die.

As they explore the game's environment and come across spore-filled rooms, players of The Last of Us come upon decaying bodies that have succumbed to the illness.

Gas masks are necessary in the game to walk through these locations safely, but it seems that the upcoming HBO series may change how the Cordyceps infection works.