First of all, let us dismiss magical, supernatural, zombiism. Dead people coming “alive” and eating brains. It’s not entirely impossible (resorting to implants, one can remote-control an organism), but we are talking here about natural zombiism.
Natural zombiism is the transformation of a living being into something that bevaves like a zombie. A parasite (virus, bacteria, fungus) overrides the being’s will and takes control over its actions, making it serve the purpose of the parasite.
Usually, a parasite’s purpose is simply to reproduce itself, perpetuate by either infecting other organisms or completing its reproductive cycle inside another host.
So, the purpose of a natural zombie is to either infect others or to get eaten by a potential host.
Ants are the first victims of zombiism. A type of fungus (no, actually 160 types of fungi have been identified, so far), can infect an ant and control what it does. This has been observed in the ant specie Polyrhachis armata in Thailand. The fungus makes the ant leave its colony, bite into the vein of a leaf, upside down, at the time of the day where the colony is active all over the place, and then the fungus builds up pressure inside the ant’s head (hard exoskeletton). Once the fungus punches a hole through the head, the built-up pressure causes an explosion, shooting spores all over the other ants, who then get infected.
Such cases of zombiism have also been observed in some bugs, crabs and spiders. But these arthropods are rather simple organisms, they can’t be compared to humans, can they ?
No, they can’t, but some mammals can.
Take mice and rats. A parasite known as “toxoplasmosis” can infect these little mammals when they come in contact with cats or cat poo. The parasite makes the mouse or rat (let’s just reduce it to rat, to keep it simple) very nervous, agitated, it can’t sit still. Also, the parasite reduces the rat’s sense of danger, and makes it attracted to cat smell. In other words, the parasite manipulates the rat in order to make sure that it gets eaten by a cat. This allows the parasite to complete its reproduction cycle inside the cat (a host, but without any symptom of infection) before being transmitted to other rats.
We’ve talked about mice and rats. Well, although it doesn’t look like it at first sight, they are genetically very close to us humans. And as it happens, the parasite toxoplasmosis also works on us.
Well, it doesn’t make us fall prey to our cats, we are a little bit too big to get eaten by those, we are just an “accident”, a dead-end, for the parasite. Still, it changes us.
In humans, toxoplasmosis causes some of the same symptoms as in rats : anxiety and diminished sense of fear (possibly attraction to cats as well). Interestingly, men and women react oppositely to anxiety as anxious men tend to become more introverted and anxious women tend to become more extraverted. The diminished sense of danger doesn’t cause much harm in our comfortable society where we don’t need to outrun lions and catch buffalos for food. However, many of us perform regularily a dangerous activity : driving a car. Scientists believe that many cases of reckless driving could be linked to toxoplasmosis. It doesn’t turn us into road-rage maniacs, but it does reduce our sense of danger, making us take more risks. How much more is still to be determined.
Other parasites control us too… take something as simple as the common cold. There are 600 types of virus out there that cause the same illness. What they do is infect our respiratory tract, we get a sore throat. Then, the body defends itself : fever, coughs, sneeze and fatigue. These symptoms are not those of the infection, but those of our body fighting the infection. (This is why it’s a bad idea to take aspirin against the fever, it makes us feel better but also slows down the process of healing). So, coughing and sneezing help us expell them nasty virusses… but that’s exactly what they wanted us to do ! We infect other people through our coughing and sneezing, it’s part of their strategy. Our own defenses are manipulated by a virus.
The common flu does the same, and may also have added a trick. According to some research, before the acute symptoms of the flu, we tend to be more sociable. Apparently, the virus manipulates us into seeking more contact with other humans, in order to infect them.
So, it is indeed possible for a parasite to manipulate us. Not to the point of zombiism, as we still have our free will. But technically, a parasite could override larger chunks of our mind, it only depends on what it wants us to do. In theory, it could make us bite one another. Think of a bacteria or fungus that needs to be injected directly under the skin via a bite. But it probably won’t turn us into brainless maniacs.
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