Ophiocordyceps unilateralis is a parasitic fungus, coming from the fungus family Cordyceps. This malignant affliction commonly affects insects and arthropods. It is commonly, but not exclusively, found in tropical and temperate rain forests in the Americas, and in smaller cases worldwide.
Traveling through airborne spores, a Cordyceps fungus will infiltrate its species-specific host and control its nervous system, directing it in a certain direction to make future delivery of spores easier before the fact. The host may live under the influence of a Cordyceps fungus for some time, though the fungus will sap its organs and tissue and soon enough kill it. Cordyceps received much of its press and partially inspired the development of The Last of Us by appearing in the BBC documentary Planet Earth. The Cordyceps appeared in the Rain Forests episode, where an ant was shown shaking uncontrollably and scratching at its head. A different, uninfected ant was shown carrying the afflicted worker away from the nest and into the trees, leaving it convulsing on a branch.
There, the Cordyceps fungus revealed why it is now so infamous. The documentary showed a period of a fast-motion videography, where the now-dead ant was shown as a lifeless husk. As the shot went on, a fruiting body became apparent as it pierced from the ant's head and growing to about the length of the ant's body. The documentary went on to show the corpses of different insects and arthropods (including spiders) and described that most if not all Cordyceps fungi were evolved to infect a certain type of small animal. It can be safely described as a neuroparasite, given its influence over the victim's nervous system and likely its brain as well.
In The Last of UsEdit
Before the events of The Last of Us, it is revealed that the bulk of humanity has been infected with what seems to be an invasive parasite similar in symptoms and effects to a Cordyceps fungus. The Ophiocordyceps unilateralis found in the game is fungus that is evidently evolved from the Ophiocordyceps unilateralis strain that we know, the prime difference being that this strain infects only human subjects, while the modern strain is specific to certain species of insect, including ants. The other main difference is that, instead of directing the host into a convenient place for the fungus to grow and spread spores right away, the in-game fungus would direct them into harm's way in a classic, "zombielike" quest to infect uninfected individuals by way of a bite. The subject can only be infected alive, contrary to other survival horror games such as Dead Space, where the host dies before mutating. The usage of gas masks by survivors is present in the game, due to the fact that the fungal spores are airborne, which upon entering a human's lungs, can infect them (Joel has one such gas mask strapped to his hip). This is also evident in some of the concept art (shown here).
VideosEditThe Last Of Us - Nature Encroaches(04:06)