Wolves boosted by parasite more likely to lead pack: study

Wolves boosted by parasite more likely to lead pack: study

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

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

It is estimated that between 30-50 percent of people worldwide are infected with the parasite, which remains lifelong as cysts of dormant tissue. However, people with healthy immune systems rarely have symptoms.

While some studies have reported a link between people having brain parasites and increased risk-taking, other research has disputed these findings and no definitive link has been proven.

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

Researchers from the Yellowstone Wolf Project analyzed blood samples from nearly 230 wolves and 62 cougars — big cats known to spread the parasite.

They found that infected wolves were more likely to invade deeper into cougar territory than uninfected wolves.

Infected wolves were also 11 times more likely to leave their pack than parasites-free wolves, the study said, indicating a higher rate of risk-taking.

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

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

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

Cassidy said it was only the second study of the effect of T. gondii on a wild animal, after research last year showed that increased boldness in infected hyena cubs made them more likely to approach and kill lions in Kenya.

Laboratory research also found that rodents with the parasite lose their instinctive fear of cats – putting them in 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 demonstrate causality.

“A wolf born at risk may simply be more likely to venture into cougar territory and become infected with 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 concluding that the infection could increase the risk in humans.

“There is a lot about human behavior that is different from other animals,” he told AFP.

People often become infected with T. gondii by eating undercooked meat – or through their pets, especially when cleaning 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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