How would Ophiocordyceps unilateralis need to be modified to make a realistic “The Last of Us” apocalypse scenario?

Question

In the story I am writing, the United States never pulled out of Vietnam, with the conflict continuing into the present day. During this time, the United States decided to use Vietnam to secretly field test illegal bioweapons (since the USBWL was never disestablished), one of them being a genetically modified version of Ophiocordyceps unilateralis. The modified version of the fungus was designed to do two things: make the host kill and eat members of its own species, and use the nutrients from the consumed flesh to produce spores to spread to new hosts.

So, my questions are:

1) What modifications would be required to allow Ophiocordyceps unilateralis to infect humans?

2) How would Ophiocordyceps unilateralis modify the host's brain to cause the host to exhibit the behaviours stated above?

Answer 1

As far as I’m aware, our understanding of how mind control works is essentially based on hormones and chemical signals. These are sent through the host’s nervous system against their will in order to create the desired reaction. Imagine having an assembly line that delivers numbers to a terminal and the number “3” will cause a specific reaction. The facility runs as normal, but someone has broken in and is constantly throwing 3’s into the system. You could essentially “control” something this way. A potentially dark side effect of this is that the host is completely aware it is being manipulated, but is powerless to do otherwise.

Additionally, a species of mind controlling parasite called leocochloridium which infects snails sends additional signals to castrate the snail. This ensures more energy available to be used for the parasite’s intentions. Infected snails are effectively “super snails” and travel much faster than normal. Your form of cordiceps could do something similar to the infected host; shutting down additional bodily systems to provide energy for other areas. Basically, after all this, you’re looking at very primal, hunger-fueled monsters built for one single purpose: hunting. Hope this helps.

Answer 2

After reading this article, I have an idea.

It's mentioned that there are probably about 1000 different kinds of Ophiocordyceps, and that it and ants have adapted over time both in arsenal and defense. It behaves similar to that of yeast that is found in beer.

To answer your first question, I think it would be an interesting idea in a story to find a way for people to have a yeast infection, perhaps through beer (any other ways, sure).

How would it modify the host's brain (second question)? The host would have to be dead, with significant fungal cells in the body/brain. Then, similar to the ant, the human (now dead human) would behave the same way:

While the manipulated individual may look like an ant, it represents a fungal genome expressing fungal behavior through the body of an ant. - quote from article link above

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In conclusion, this kind of outbreak would start by people drinking an especially yeasty modified beer that will cause a kind of yeast infection in the brain... killing the host... and the behavior is fungal in nature.

So your characters should think twice about drinking that cheap skunky beer.

Answer 3

First, you would have to engineer a Ophiocordyceps species that is interested in human targets, which may be a challenge as human are significantly bigger and might be harder to infect, or at least maintain the infection. The parasite would have to be able to either neutralize the host's immune system or avoid it.

However, since humans are much bigger animals, the fungus would probably have access to much more nutrients and therefore produce much more spores (or at least you could engineer it to do so).

To infect more humans, you could "teach" the fungus to lead the host to ventilation systems but it might be a bit cold and dry for the fungus to grow. Doing so would allow the infection to spread into a whole building. It needs to be able to find a "comfortable" place to grow from which it can spread its spores. From what I know, it needs to be a shady, humid and warm place.

As for the mind control, I do not have sufficient knowledge to know in details how the fungus controls the host. Maybe it could act on synapses to modify brain signals.

I am not sure if the fungus would benefit from an aggressive host. Judging by the original fungus' behaviour, it kills the host once it wants to spread its spores. Maybe it is because it needs as much energy as possible to create spore. If so, maybe the fungus would only need to consume part of its host to start producing spores and aggressiveness would allow the host to get closer to non-infected humans and ensure the spread of spores directly on non-infected individuals.

Answer 4

Have you considered making it a sexually transmitted disease?

The kind of ant infection you are interested in is very unlikely to scale to a whole human body. It operates not through hormones or neurotransmitters, nor brain manipulation, both of which are more likely to work on a large complex organism. Instead it overrides existing motor controls and sends signals to ant muscles directly, while the ant might be fully conscious. Even if it somehow gains the processing power to navigate a human body through complex environments, it would be a slow and inefficient process and give people too much time to notice and react. Humans also have a more powerful and very different immune system.

Instead, shallow fungal infection is much easier and faster, and much less alarming than total body control. To achieve the goal of killing and eating humans, it could be sexually transmitted and destroy and consume human reproductive cells and fetuses, which at least some people consider human beings - even if you disagree, the goal of destroying humanity would still be achieved. To speed up spreading, it could use its muscle-controlling powers to affect human sexual behavior and make its host continually stimulated and have more pleasure/last longer, so they will have sex with more people(but not so obvious to be alarming), and this would be easier and require less "intelligence" than controlling the whole body. People may even willingly get infected even after it's found out if it doesn't otherwise negatively impact their lives too much. If you are being nice, just stop there. If you want to make it slowly destroy the host or turn them into classical zombies, this method can buy you time.

A zombie apocalypse doesn't have look like "The Last of Us". In some sense, what the organism's behavior is helping to reproduce and evolve is what's really in charge. We could be living more or less normal lives and still be scientifically zombies if all human achievements and desires and relationships would only serve our invisible fungal masters.

Answer 5

Zombie, Vampire and Werewolf myths are all loosely based on Rabies which is a much shorter biological reach. That fungus is particularly adapted to infect specific ant species, and you have to go from that all the way to humans while rabies already does some of what you want and it works on most mammals already.

In humans, that fungus' intrinsic workings would have to work on fundamentally different:

• circulatory system and chemistry
• nervous system

In addition, with increasing degrees of certainty, I don't believe ants have

• dedicated lymphatic systems
• internal skeletons
• medicine

It's a scary fungus with incomprehensibly complex interactions, but ants are far simpler than humans. Perhaps rabies gets some DNA from Ophiocordyceps unilateralis or vice-versa. One could never hybridize the two because one is a virus and one is a fungus.

Answer 6

If your pathogen shut off the satiation circuits in the human brain it could create voracious humans who would want to eat everything. If it also damaged the disinhibition function of the fore brain and the mirror neurons that create empathy with others, it would turn humans into voracious eaters who couldn't help themselves and wouldn't even feel bad about it. If it could also make other humans smell absolutely delicious, watch out!