Cordyceps Brain Infection (CBI) is a parasitic fungus that has devastated mankind in The Last of Us.
The Last of UsEdit
In The Last of Us, nearly 60% of humanity has been either killed or infected by a cordyceps fungus, referred to as Cordyceps Brain Infection. The fungus grows while the host is still alive, taking away their higher brain function (and with it, their humanity), and causing the infected to become hyper-aggressive (stage 1).
As the infection progresses, they lose their sight as a result of fungal growth over most of the head and damage to their visual cortex (stage 2). These infected develop a primitive form of echolocation to compensate (stage 3). Over a very long time, they will eventually develop hardened fungal plates over most of their body (stage 4). If the fungus kills the host, the host's body will grow stalk-like fungal projections which release infectious spores. The infection can also be spread through bites from living hosts. Hosts can only be infected while alive, as the fungus is unable to infect dead bodies.
The infection seems unable to spread in open air areas, such as the countryside, although it thrives in underground areas, especially sewers and subway tunnels.
In the Left Behind DLC, during her search for medical supplies, Ellie discovers that an attempt was made by Captain Regan to stop the infection from spreading throughout the body of her fellow survivor Private Ellis by quickly amputating his bitten right arm. Regan chose not to follow the military's Infection Protocol to kill Ellis after having already killed Officer Caulfield when it was discovered he was bitten earlier. It is implied that the amputation may have stopped Ellis from becoming infected, but not knowing the future consequences of Regan's actions had made both of them doubtful and fearful of whether this course of action was right or wrong. Ellis later shot Regan dead out of fear that she would kill him, and later bled out and died in an airduct after escaping from some infected.
- An episode of the BBC documentary Planet Earth entitled "Jungles" features an infected ant being killed by ophiocordyceps unilateralis, as well as showing a variety of other insects and arachnids that were killed by different species of the fungus. This scene partially inspired the development of The Last of Us.
- Cordyceps spores can be seen blowing away as a loading screen when booting up the game. Spores are also plainly visible in the air.
- It is stated in a newspaper, in Joel and Sarah's house in the beginning of the game, that the Cordyceps outbreak spread to humans due to infected crops.
- Despite the CBI being based and classified from the cordyceps as a pathogen under the 'fungi' class, which usually fatal to insects rather than humans (in real world term). In the game however, the fungi became an epidemic which acts as both infectious fungi and virus. The cordyceps itself is considered as mutated by a certain 'virus' which somewhat like how bacteriophage (a virus which breeds and kill a bacteria from the inside) does. Like the description, the mutated cordyceps could have a much more horrendous infection to its host and rather, killing them or 'abominating' from the inside, like bacteriophages.
- In reality, it is quite impossible for humans to be fatally infected by the ophiocordyceps genuses, but may undergo behavioural change or 'disorder'. Since humans are easier to disect (in terms of removing foreign substances or matter) than insects (also body size can also have different outcome for the infection), normal cordyceps would take weeks or months for it to be fatal.