In 2016 scientists found a parasite is able to manipulate the behaviour of its chimpanzee hosts, making them morbidly attracted to the odour of their only natural predator.
Toxoplasma gondii is a tiny single-celled cat parasite that also infects a range of other mammals and birds as intermediate hosts, forming cysts in their brains and other organs.
These hosts must be eaten by a feline if the parasite is to complete its life-cycle.
There is good evidence that the parasite aids its own transmission to cats by modifying the behaviour of its intermediate hosts so that they are more likely to be killed by felines.
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Scientists working in Gabon found that infected chimpanzees are attracted to the urine of leopards. Crucially, however, this fatal attraction did not extend to the urine of lions or tigers, neither of which prey on the apes.
“This suggests that it could be real parasite manipulation,” said the leader of the research Clémence Poirotte, of France’s Centre d’Écologie Fonctionnelle et Évolutive.
Humans can contract toxoplasmosis, too – those who are infected suffer from concentration problems and slow reaction times. Intriguingly, there is some evidence that they are attracted to the urine of domestic cats, even though these particularfelines don’t eat humans.
“The behavioural changes reported in humans are generally assumed to be side effects of a manipulation that evolved in appropriate hosts, like rodents, to increase parasite transmission to cats,” Poirotte told BBC Wildlife.
“It is possible that the parasite acquired the ability to manipulate our ancestors when they were predated by big cats, and that such an olfactory modification in infected humans nowadays is an ancestral legacy of this evolutionary past.”
