Parasite could help wolves become pack leaders

To become chefs, not everyone is equal. This is shown by a study that suggests that wolves infected with the common parasite are much more likely to establish themselves as leaders of their pack. This colonizes the brain and pushes the host to take risks.

This single-celled parasite, called Toxoplasma gondii, breeds only in cats and felines, but can infect any warm-blooded animal. It is estimated that 30 to 50% of the population is infected with this parasite, which remains there for life as dormant tissue. The human immune system usually prevents any symptoms from appearing.

Research has established a link between its presence in the human brain and an increase in risky behavior and aggression. Others dispute the existence of such a link. The study, published Thursday in the scientific journal Communications Biology, is based on a 26-year observation of gray wolves in Yellowstone National Park in the United States. Researchers from the Yellowstone Wolf Project analyzed blood samples from 230 wolves and 62 cougars. The latter are known to spread the parasite when communicating with wolves.

Infected hyenas will move closer to lions

Their study found that an infected wolf is eleven times more likely than an uninfected wolf to leave its pack, indicative of a greater risk appetite. And an infected wolf is 46 times more likely to become a pack leader, according to a study that recalls that this role usually goes to the most aggressive and adventurous person.

These three findings provide “rare evidence that a parasitic infection affects the behavior of a population of wild mammals,” the study says. “Being more fearless is not a bad thing in itself, but it can shorten the lives of animals because their decisions can endanger them more often,” explained Kira Cassidy, co-author of the study.

Another study published last year concluded that the bolder, vermin-induced behavior of young hyenas in Kenya makes them more likely to approach lions and be bitten. The same scenario will work with rodents infected with the parasite: they lose all instinctive fear of their first predator, the cat, which is the preferred host for Toxoplasma gondii.

A parasite that can seriously affect a person

Praising the results of the wolf study, William Sullivan, professor of pharmacology and toxicology at Indiana University, warns that they do not prove causation. “A wolf with a risky temperament may simply be more likely to venture into cougar territory and contract toxoplasmosis there” (caused by the parasite in question), notes a professor who has studied the parasite for more than 25 years.

But “if the results are correct, they suggest we are underestimating the impact of Toxoplasma on ecosystems,” he adds. In humans, the parasite primarily affects immunocompromised individuals and causes toxoplasmosis, a disease that can damage the brain and eyes. Infection usually occurs when eating too raw meat or when caring for a cat, in particular, when cleaning her bedding.

Ajay 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 notes.