Wolves boosted by parasite more likely to lead pack: study

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Paris (AFP) – Wolves infected with a common parasite are much more likely to become their pack leader, according to a new study that suggests a brain-dwelling invader encourages its host to take greater risks.

The single-celled parasite Toxoplasma gondii reproduces sexually only in cats, but can infect all warm-blooded animals.

An estimated 30-50 percent of people worldwide are infected with the parasite, which remains as dormant tissue cysts throughout life. However, people with healthy immune systems rarely have any symptoms.

While some studies have linked people with a parasite in the brain to an increased risk, other research has questioned these findings and no definitive link has been shown.

A new study, published Thursday in the journal Communications Biology, used 26 years of data on gray wolves living in Yellowstone National Park in the United States to examine how the parasite might affect their behavior.

Scientists from the Yellowstone Wolf Project analyzed blood samples from nearly 230 wolves and 62 cougars – big cats are known spreaders of this parasite.

They found that infected wolves were more likely to penetrate deeper into a cougar’s territory than uninfected wolves.

Infected wolves were also 11 times more likely to leave their pack than wolves without the parasite, the study said, suggesting higher levels of risk-taking.

And an infected wolf is up to 46 times more likely to become a pack leader, the researchers estimated, adding that more aggressive animals usually win the role.

Study co-author Kira Cassidy told AFP that while “being bolder is not necessarily a bad thing”, it could “reduce the survival of the bravest animals because they may be more likely to make decisions that put them in danger”.

“Wolves don’t have the survival room to take too many more risks than they already have.”

Cassidy said this is only the second study of T. gondii’s effect on a wild animal, after research last year found that increased boldness in infected hyena cubs made them more likely to approach — and kill — lions in Kenya.

Laboratory research has also found that rodents with the parasite lose their instinctive fear of cats – bringing them into the hands of the only host where T. gondii can reproduce.

William Sullivan, a professor of pharmacology and toxicology at the Indiana University School of Medicine who has studied T.gondii for more than 25 years, called the wolf paper “a rare gem.”

However, he cautioned that such an observational study cannot prove a causal relationship.

“A wolf that is born risky may simply be more likely to venture into cougar territory and contract toxoplasma,” he said.

But “if the findings are correct, they suggest that we may be underestimating the impact of Toxoplasma on ecosystems around the world,” he added.

What about people?

“That’s the million dollar question,” Sullivan said, adding that “nobody knows for sure and the literature is mixed.”

Ajai Vyas, a T. gondii expert at Singapore’s Nanyang Technological University, cautioned against inferring that the infection could increase the risk in humans.

“Human behavior is very different from other animals,” he told AFP.

People often become infected with T. gondii by eating undercooked meat – or through their cat, especially when they clean out their litter boxes.

In some cases, especially in people with weakened immune systems, T. gondii can lead to toxoplasmosis, a disease that can cause brain and eye damage.

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