Much to my surprise, I’ve become a bit of a zombie junkie.

I’m a big fan of the Walking Dead television show and zombie films in general (I could watch Shaun of the Dead endlessly). I’ve been intrigued and spooked by the genre’s post-apocalypic visions of a humanity overrun by a mysterious virus that brings the dead back to life—only to stalk the living.

While it doesn’t necessarily speak to the kind of speculative fiction that I normally enjoy, it does offer some food for thought as far a the science is concerned. And it got me thinking: Could such a thing ever happen? Moreover, given the potential power of future technologies, could a ‘zombie virus’ be deliberately engineered? The more I thought about this, the more I became convinced that such a thing might actually be possible.



Solanum virus
According to zombie canon, it’s a virus called Solanum that is responsible for converting the living to the undead. According to the Zombie Survival Guide, the virus works by traveling through the bloodstream from the original point of entry to the brain where it uses the cells of the frontal lobe for replication, destroying them in the process. During this period, all bodily functions cease and the infected subject is eventually pronounced “dead.” The brain remains alive but dormant while the virus mutates its cells into a completely new organ.

Once the mutation is complete, this new organ reanimates the body—but typically to a form that bears little resemblance to the original corpse. Some bodily functions remain constant, others operate in a modified capacity, and the remainder shut down completely.

The result of the transformation is a zombie, a member of the living dead.

But it doesn’t stop there. The reanimated corpse develops an insatiable appetite for human flesh, the brain in particular. It is through the relentless stalking and attacking of the living that zombies attempt to satiate their appetites, while spreading the virus to their surviving attack victims.

Solanum is 100% communicable and 100% fatal. While the virus is neither waterborne nor airborne, infection can only occur through direct fluidic contact. A zombie bite is the most common vector for transferring the virus, but it’s not the only one. Humans can be infected by brushing their open wounds against those of a zombie or being splattered by its remains after an explosion.

As for the zombies, there is no cure. Nor can their relentless thirst for the living be quenched. They are single-purpose automatons, stalking the living until their bodies have completely rotted away, or their brains destroyed.



The zombies among us
This might all sound rather fantastical, the stuff of cheesy horror flicks, but the concept is not as outlandish as it might appear. Natural selection has, quite disturbingly, produced a number of viruses that, for all intents and purposes, turn their hosts into virtual zombies.

Take mind controlling parasites, for example. These are viruses and simple organisms that have evolved such that they can alter the behavior of their hosts. Essentially, they cognitively re-engineer their victims, turning them into their transmission vectors. It is not uncommon for organisms to leech off several different species in this way as part of their reproductive cycle.

For example, there is Plasmodium gallinaceum, more commonly known as malaria. It’s been known for some time that this protozoan uses mosquitoes as its vector. What has not been known until recently, however, is how malaria alters the blood sucking behavior of mosquitoes. Malaria has had a significant impact on the evolution of mosquitoes and their behavior, much like flowers, have contributed to the evolution of its pollinators, namely bees and other flying insects. Specifically, a mosquito will continue to search for victims until it reaches a threshold volume of blood. When it hits this threshold point, it stops host-seeking. It is thought that the stage-specific effect of the malaria parasite on host-seeking behavior is likely to be an active manipulation to increase its transmission success.

Then there’s Dicrocoelium dendriticum. It’s a virus that primarily infects sheep—but it has a rather convoluted way of going about its reproductive business. First, adult worms lay eggs in the bile ducts of the sheep and are excreted. These eggs are in turn ingested by various species of land snails and the eggs hatch in their digestive tracts. This hatching releases a compound that continues to change until it is released by the snail in the form of a slimeball. This slimeball is then eaten by ants. This eventually develops into metacercariae within the abdominal cavity of the ants. And here’s where it gets interesting (not that it hasn’t been a riveting tale to this point): the ant’s behavior is in turn altered such that it is compelled to climb to the very top of a blade of grass where it waits to get eaten by sheep. The sheep eats the grass with the ant on it and subsequently becomes infected. The cycle is complete.

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