Washington (AFP)
Hordes of undead terrorizing the neighborhood: that makes some really good horror movies, but zombies, of course, do not exist in the real world ... really?
There is actually more and more literature on parasites that can change the behavior of the animal they have chosen to host - and more and more studies showing that humans are not totally immune either. to this kind of zombie manipulations.
The subject fascinates the biologist Athena Aktipis, from the University of Arizona, who is also the author of a podcast called "Zombified" (zombified).
"More than half of the species we know on Earth are parasites," she told AFP.
An example is the Ophiocordyceps mushroom. It releases spores that, when they infect the body of a certain species of ant, allow it to take control of its motor activity.
It forces the insect to move away from its congeners and to cling to a plant, before dying, frozen by an infection. A new mushroom then grows from the victim's head, and in turn releases spores that will affect other ants, thus repeating this cycle for two to three weeks.
"We are totally convinced that the behavior of the ant is to the benefit of the fungus," says Charissa de Bekker, assistant professor of biology at the University of Central Florida, who conducts research on these two species to better understand this process of ownership.
- "Rather disgusting" -
Another example is gall wasps, targets of another parasitic wasp, the Euderus set.
Kelly Weinersmith, a professor of biology at Rice University, was part of the team that discovered this particular phenomenon. At first everything goes smoothly: the first wasp lays in a cavity formed in the wood of an oak, called a "crypt". The larva grows there, and finally chews the walls in order to exit at the end of its growth.
But when the second wasp finds one of these larvae, it places its own egg in the crypt, and the parasite then comes into action. He manipulates the first larva to become a young wasp so that the hole it digs is actually too small for it to come out, so it gets stuck there, with only the head protruding.
"Once trapped there, the parasitoid eats (the first wasp) from within," says Kelly Weinersmith. "And when the parasitoid has finished developing, he eats his host's head and goes out through his head." The process "is pretty disgusting," agrees the researcher.
- And humans? -
And if you think that none of this can happen to humans, you may have to reconsider your judgment.
The unicellular parasite Toxoplasma gondii may have affected 40 million Americans, according to the Centers for Disease Control and Prevention (CDC), and some studies have shown that it can influence human behavior.
This parasite develops originally in the cat's intestine. And he "evolved to make sure that an (infected) rat is attracted to cat urine." Thus, the rat approaches the cat, which can eat it, and the loop is closed.
"If it's not zombification, what is it?" Asks Ms. Aktipis.
Humans can become infected by eating undercooked meat, or through their pet, for example by cleaning their litter box.
Some studies have reported a link between brain infection with this parasite and some personality traits, such as aggression, although other studies have questioned these findings.
Rabies, in the same way, makes animals and people very aggressive.
But the jump in the evolution of the parasite should be considerable so that it can do to humans what it does to rats. We are still far from the hordes of zombies in the street.
But for Athena Aktipis, who organized a medical meeting on the theme of the "zombie apocalypse" last year - and is preparing another for 2020 - make the subject fun is a way to think about possible threats future.
She also recommends keeping an emergency bag with food, a first aid kit and whiskey at home to sterilize wounds - or to drink, if things go really bad.
© 2019 AFP