A zombie is eating you up from the inside

Washington – Hordes of brain-munching undead terrorising neighbourhoods make for fun television and movies, but zombies could never be real ... or could they?

There are, in fact, a growing number of documented examples in the animal kingdom of parasites that change their hosts’ behaviour – and increasing evidence that humans are not immune to zombie-like manipulations.

It’s a subject that fascinates theoretical evolutionary biologist Athena Aktipis of Arizona State University, who hosts a podcast called Zombified that applies realworld science to apocalyptic stories first popularised by filmmaker George Romero in the ’60s and now a staple horror genre.

“More than half of the species that we know on Earth are parasites,” Aktipis said.

One example is the Ophiocordyceps fungus, which releases spores that infect the carpenter ant’s body, allowing it to take over the insect’s locomotive activity.

Eventually, it kills its host by forcing it to leave its nest and bite down on a piece of vegetation which it gets stuck to as a result of a tetanus-like infection that gives it lockjaw.

The fungus erupts out of its host’s head with a mushroom-like growth called a stroma. At night, when uninfected ants are out foraging, this growth shoots out more infectious spores and the 2-3 week cycle repeats itself.

“We’re totally convinced that the behaviours that the ants show are all to benefit the fungus,” said Charissa de Bekker, an assistant professor of biology at the University of Central Florida, who is carrying out genetic research to understand the takeover process.

If you think nothing like that could ever happen to humans, think again.

The single-celled parasite Toxoplasma gondii may have infected about 40 million Americans, according to the Centres for Disease Control and Prevention.

The parasite “somehow evolved to make a rat get turned on by the smell of cat urine, so it goes up to a cat and snuggles with it, and then it gets eaten, which completes the life cycle of the toxoplasma – if that’s not zombification then what is?” said Aktipis.

People can get infected by eating undercooked meat – or through their cats, especially when cleaning out litter boxes.

Some studies have reported an association between brain infection of the parasite and personality traits such as risk-taking and aggression, though other research has disputed that.

Rabies, likewise, makes animals and people aggressive and, in some cases, makes humans extremely sexually aroused.

There’s even growing evidence that the bacteria in our gut change our behaviour, including what we want to eat, the subject of another paper that Aktipis recently co-authored. –