[LUM#9] Chimpanzee Under the Influence

[LUM Magazine] - Published on March 19, 2019 in Science and Society

What could possibly drive a chimpanzee into the clutches of its only predator, the leopard? Answer: Toxoplasma gondii. Researchers have shown that when these primates are infected with the toxoplasmosis parasite, they are attracted to the urine of their natural predator. A phenomenon of manipulation that could very well occur in humans as well…

You’re being manipulated! “You”? It’s Toxoplasma gondii, the parasite responsible for toxoplasmosis. This protozoan can only reproduce within a cat’s body, but during its wanderings, it temporarily takes up residence in numerous so-called “intermediate” hosts, such as mice, chimpanzees, or humans. To return to the cat and perpetuate its lineage, there is only one solution: to ensure that this intermediate host ends up in a cat’s stomach. To achieve this, it appears that Toxoplasma gondii is capable of “manipulating” its host. Studies have shown that mice infected with the parasite are attracted to cat urine, which increases their likelihood of being eaten.

Parasitic dead end

What about humans, one-third of whose population is infected with the parasite? Since the days when humans were still the natural prey of other animals seem long gone, the likelihood of this host ending up in the stomach of some feline is very slim. A true dead end for the parasite… “Yet numerous studies suggest that infected humans also exhibit behavioral changes: slower reaction times or reduced concentration, ” explains Marie Charpentier, a researcher atthe Institute of Evolutionary Sciences in Montpellier (ISEM).

Are these side effects of toxoplasmosis, or atavistic attempts by the parasite to break free from this human impasse? To better understand these behavioral changes, Marie Charpentier and Clémence Poirotte turned their attention to humans’ closest relative, the chimpanzee, whose natural predator has always been a big cat: the leopard.

Easy prey

“We observed the behavior of 33 chimpanzees, 9 of whom were infected with Toxoplasma,” explains Marie Charpentier. The researchers spread leopard urine in the primates’ enclosures and observed their reactions. The result: “The healthy animals avoided the leopard urine much more than their infected counterparts, who approached it more closely and seemed intrigued by the scent, deliberately moving toward the urine.” In this way, Toxoplasma gondii makes infected chimpanzees easier prey for the leopard.

The fact that apes closely related to humans are indeed manipulated by the parasite suggests that the same mechanism could be at work in humans. “The behavioral changes observed in infected individuals could be remnants of an ancient parasitic manipulation, from a time when our ancestors were prey to big cats.”

Keywords: LUM#9, LUM Magazine, Research, Health