Zombies, a cross-cultural symbol of the living undead, mindless beings on the hunt for people to infect and brains to eat. Alternatively, a PhD student in the last week before thesis submission. However you think about zombies, I’m sure you still think about them, and if you’re smart about it, you’re afraid of them. The threat of human zombification appears to have become more prominent over recent months, with ‘bath salts’ zombies showing up in America to remove people’s clothing and attempt to eat their faces. Not so sure about the nudity, but the face eating sure sound threatening.
For those who aren’t quite convinced, or who think that people who take street drugs aren’t zombies in the traditional sense – mostly because they chose to take drugs rather than falling victim to a virus or having an unfortunate incident where a man came up to them, mumbled about brains and then took a chunk out of their arm – have a look to the animal world.
Ophiocordyceps camponoti-balzani, for example, a fungus that grows on ants, forces the little soldiers to essentially become zombies. The fungus grows through the exoskeleton and bides its time after weakening the ant, until it reaches maturity and releases chemicals that cause the ant to essentially commit suicide. The ant, under the influence of the those chemicals, returns to a place with a high ant population, attaches itself to the underside of a leaf and stays there until it dies. Soon after, the fungus grows reproductive structures from within the ant’s body and releases spores onto unsuspecting ants crowds below. It’s a classic zombie story of takeover, loss of neural control, and transfer of the zombification to other creatures.
Not afraid yet? In a similar story to the plight of the ant, Entomophthora muscae fungi create housefly zombies which die in open areas. As the flies are encouraged by the fungus in their brains to stick in high areas when they die, they provide a good location for spores to be released into the air, increasing the likelihood of further fungal growth. In a different case, Spinochordodes tellinii – parasitic hairworms – infest the soft tissues inside crickets and force the insects into water, causing them to drown themselves so the worms can breed.
Toxoplasma gondii © Copyright Microbe World and licensed for reuse under this Creative Commons Licence
Still nothing? Try Toxoplasma gondii, a protozoan which increases dopamine levels in the area of rodent brains associated with fear: the amygdala. The increased neurotransmitter levels create a sensation of pleasure which overrides the fear sensation that the amygdala would ordinarily produce, preventing the natural escape response that rodents would feel when faced with feline predators. Once eaten by the cats, the rodents are digested and the protozoan escapes into the cat’s digestive system, allowing it to be excreted and re-ingested by the next unfortunate rodent.
Keep in mind that with that last one, rodents are mammals, only a few steps away from humans. And, T. gondii can and does infect humans, though it causes less severe reactions that range from paranoia to decreased reaction time, with less jumping between feline teeth.
So if you’re not afraid yet, despite numerous zombies in popular fiction, articles about zombies in the international news, and stories of zombie fungi infecting non-human life forms, you might need your amygdala checked.
Zombie Parade – DSC 0533 ep © Copyright Eric.Parker (Erik Parker) and licensed for reuse under this Creative Commons Licence