Wolves emboldened by parasite more likely to lead the pack: study

Wolves emboldened by parasite more likely to lead the pack: study

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Paris (AFP)- According to a new study, wolves infected with a common parasite are much more likely to become the leader of their pack, suggesting that the brain 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 and 50% of people worldwide are infected with the parasite, which remains for life as dormant tissue cysts. However, people with healthy immune systems rarely show symptoms.

While some studies have reported an association between people having the parasite in their brains and increased risk taking, other research has disputed these findings and no definitive link has been proven.

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

The Yellowstone Wolf Project researchers analyzed blood samples from nearly 230 wolves and 62 cougars – the big cats are known to spread the parasite.

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

Infected wolves were also 11 times more likely to leave their pack than wolves without the parasite, the study says, indicating a higher risk-taking rate.

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

Study co-author Kira Cassidy told AFP that while “being bolder isn’t necessarily a bad thing” it can “reduce the survival of the boldest animals because they might take decisions that put them more often at risk”.

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

Cassidy said this was only the second study of the effect of T. gondii on a wild animal, after research last year found that the increased boldness of infected baby hyenas made them more likely to approach – and be killed by – lions in Kenya.

Laboratory research has also revealed that rodents carrying the parasite lose their instinctive fear of cats, pushing them into the hands of the only host where T. gondii can reproduce.

William Sullivan, a professor of pharmacology and toxicology at 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 could not show causation.

“A wolf that is a born risk-taker may simply be more susceptible to venturing into cougar territory and contracting Toxoplasma,” he said.

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

What about humans?

“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 Nanyang Technological University in Singapore, cautioned against the idea that infection could increase risk taking in people.

“There are many things in human behavior that are different from those of other animals,” he told AFP.

People are often infected with T. gondii by eating undercooked meat – or via their pet cat, 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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