Contagion in The Last of Us occurs in a very similar way to pathogens in other apocalyptic stories. The infected, in general, become violent and bite healthy people, transmitting the fungus that little by little ends up taking over their organism. The difference is that often in other plots of this type, the disease-causing pathogen is a virus. In fact, it is usually some type of rabies virus mutation. And this, in reality, has its explanation.
Fungi, like the Cordyceps that appears in the series, are transmitted by spores. In real life, this usually infects the ants, causing them to climb to the highest part of the trees, where the fungus finally leaves its body and releases the spores more efficiently. It has nothing to do with what we see as contagion in The Last of Us.
Neither the ants nor the rest of the arthropods that may be affected become violent. And they don’t bite their victims either, so the contagion is different. This is not objectionable. After all, The Last of Us is a fictional plot. However, in real life there are other pathogens that could be the pieces that make up the fictional fungus of the video game and the series. From the rabies virus to the protozoan that causes toxoplasmosis.
Contagions in The Last of Us are much more like rabies
Contagion in The Last of Us occurs when the infected bite healthy people. Therefore, initially it could be said that it occurs through saliva. However, in the second chapter of the series it is observed, both in the corpse of patient zero and in the infected person who kisses Tess, that a kind of rootlets or tendrils are born from her mouth.
These would be the masses of hyphae, known as rhizomorphs, that many fungi use to explore and expand. Therefore, rather than through saliva, it would be through this kind of roots.
However, we have already seen that with Cordyceps the most common is that it is transmitted by spores released from the corpse of its victims. Yes, the rabies virus is transmitted through bites. In fact, this pathogen has several peculiarities that make it cannon fodder for pandemic apocalypse plots.
This is so because, as often happens in these stories, the virus affects the behavior of those infected at many levels to facilitate its spread through bites. On the one hand, it makes them more violent. There is more to see what happens to rabid dogs. And, on the other, it causes them a great aversion towards water. This is because the more concentrated the virus is in the saliva, the easier it is to spread through bites. If the infected drink water, the saliva is diluted and this is something that the rabies virus does not like. Therefore, behavior is also modified in this regard.
It should be remembered that viruses do not have consciousness and that they do not do so on purpose. Simply, evolutionarily, based on mutations, they have reached points that are very beneficial for them.
Infected, manipulated and violent
Apparently, contagion in The Last of Us occurs when the infected attack violently. However, the authors of the series have recognized, with Tess’s kiss scene, that this is so because, in reality, the victims resist. If they remain quiet and wait for the contagion, as she does, they could pass their hyphae to her peacefully.
Leaving this aside, what is clear is that the Cordyceps manipulates them to take them to the place where they can spread. This does happen —in part— with the fungus in real life. once it releases in the organism of the ants some substances that affect their brain and produce changes in behavior, such as the need to climb to the highest treetops.
The case of ‘Toxoplasma gondii’
Another pathogen that does that, in an even more impressive way, is Toxoplasma gondii. Known to cause toxoplasmosis, this protozoan has a life cycle that is divided into two parts.
In the first stage it can reproduce in any of the animals known as “warm-blooded”. For example, this includes mammals and birds. However, the second must occur in cats. That is why he manipulates the former to take him to the latter.
In this first stage, it proliferates inside some cysts that are located mainly in the muscles and brain of the hosts. Therefore, if a cat eats them, it will go directly to its body. This means that Toxoplasma gondii has also developed the ability to manipulate its victims so that they take it where it needs to go. For example, infected mice have been shown to be fearlessly attracted to cat urine, and chimpanzees to leopard urine.
Thus, when the cat eats the other animal, the protozoan goes directly to the intestines, where it ends its life cycle. In addition, from there it goes outside in its feces, with which new infections can occur. For example, humans can get it by handling their cat’s feces or eating poorly washed vegetables.
It also affects humans
Generally, Toxoplasma gondii does not cause serious effects in humans. It is only usually dangerous for immunocompromised people and fetuses, hence pregnant women must be very careful not to become infected.
However, there have been cases of infected people who show great impulsiveness. After all, that is what the protozoan does with mice and chimpanzees as well. Cancels the feeling of fear and makes them more impulsive. It has even been linked to cases of schizophrenia, although this needs to be studied further.
What is clear is that both the rabies virus and the Toxoplasma gondii protozoan actually produce something similar to the contagion of The Last of Us. Fortunately, they haven’t teamed up to trigger an apocalypse. That would also be very scary.