(Paris) Wolves infected with an ordinary parasite are much more likely to impose themselves as the leader of their pack, according to a study which suggests that the intruder, which colonizes the brain, pushes its host to take risks.
Toxoplasma gondii, a single-celled parasite, breeds only in cats and felines, but can infect any warm-blooded animal.
It is estimated that between 30 to 50% of the human population is infected with the parasite, which remains there for life in the form of dormant tissue. The immune system of humans usually prevents the onset of any symptoms.
Studies have established a relationship between its presence in the human brain and an increase in risky behavior and aggression. Others have disputed the existence of such a link.
The study published Thursday in the scientific journal Communications Biology is based on 26 years of observing gray wolves in the United States’ Yellowstone National Park.
Researchers from the Yellowstone Wolf Project analyzed blood samples from 230 wolves and 62 cougars. The latter are known to spread the parasite in their interactions with wolves.
Increased danger
Their research established that an infected wolf is eleven times more likely than an uninfected wolf to leave its pack, which is characteristic of a greater propensity to take risks.
And an infected wolf is 46 times more likely to become leader of the pack, according to the study, which recalls that this role normally falls to the most aggressive and adventurous individual.
These three findings provide “rare evidence of a parasitic infection influencing behavior in a wild mammalian population,” according to the study.
“Being more fearless isn’t in itself a bad thing, but it can shorten animals’ lives because their decisions can more often put them at risk,” said study co-author Kira Cassidy.
Another study published last year concluded that bolder, parasite-induced behavior in young hyenas in Kenya made them more likely to approach lions and be bitten.
The same scenario would be at work in rodents infected with the parasite: they lose all instinctive fear of their first predator, the cat, which is the host of choice for Toxoplasma gondii.
The impact of Toxoplasma
While praising the wolf study’s findings, William Sullivan, professor of pharmacology and toxicology at Indiana University, cautions that it does not prove a causal relationship.
“A wolf with a risk-taking nature might simply be more inclined to venture into cougar territory, and contract toxoplasmosis there” (caused by the parasite in question), notes the professor, who has studied the parasite for over 25 years.
But “if the results are correct, they suggest that we are underestimating the impact of Toxoplasma on ecosystems”, he adds.
In humans, the parasite primarily affects immunocompromised people, and causes toxoplasmosis, a disease that can damage the brain and eyes. The infection generally occurs by the absorption of too raw meat, or through the care given to his cat, in particular by cleaning his litter.
Ajai Vyas, a parasite specialist at Nanyang University in Singapore, doubts that such an infection in humans could lead to risky behavior. “Human behavior is very different from that of other animals,” he points out.