David EngelthalerBy David Engelthaler
Adjunct Research Faculty, Biology
Director of Programs, TGen North

It may be because Halloween is near or because the next season of The Walking Dead just kicked off, but lately a lot of people are asking me whether a zombie apocalypse could really happen.

Most are surprised when I tell them, “Yes, it already is—kind of.”

That’s because a zombie apocalypse is in the eye of the beholder.

Imagine you’re a cricket, and you get infected with a parasite known as Spinochordodes. This parasite—a hairworm—not only grows inside you, it actually starts to take over your movements, ultimately forcing you to plunge into a water source so it can break out of you in search of another hairworm to reproduce with.

Or maybe you’ve heard of the “zombie ants” that get infected with a fungus called Ophiocordyceps, which also controls their neuro-motor system. An infected ant crawls to the underside of a leaf, clamps down on the central leaf vein and waits as the fungus consumes its inner tissues, bursts out of its head and sends spores floating to the ground to begin the process all over again.

While confined to the insect world, we’d certainly consider it a kind of apocalypse if these infections were transmitted between humans.

But humans do get infections that control our actions for the primary purpose of further spreading the infection. Consider the rabies virus, which spreads from the bite of an infected mammal—including humans. The virus travels up the nearest neuron to the central nervous system and eventually the brain. Infected animals/people can become stuporous and lose partial control of limbs—which is kind of zombie-like. They can become very aggressive and actually bite other people—which is very zombie-like—and further spread the virus, which moves to and replicates in the salivary glands.

Although tens of thousands of human rabies cases still occur—mostly in Asia and Africa—human-to-human rabies, thankfully, is very rare. There are a number of other neuro-tropic (i.e., brain-seeking) human infections, but fortunately not to the extent of causing the zombie apocalypse.

But could a new virus or pathogen just evolve out of nature and wipe us out? The true answer: Maybe. New pathogens occur all the time. Remember SARS from 2003? We had no way to vaccinate or treat it, and it killed more than 8,000 people before we could quarantine and isolate it. A new version is back—called MERS, for Middle East Respiratory Syndrome—and it has a fatality rate more than four times that of SARS, and again we have no treatments or vaccines. There are others as well, with names like Nipah, Hendra and ABLV.

So while we may not be having a zombie apocalypse anytime soon, who knows what is out there lurking in nature, just waiting to emerge? Happy Halloween!