Study: Wolves encouraged by parasites are more likely to lead the pack

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        <span class="t-location">Paris (AFP) - </span>A new study suggests that wolves infected with a common parasite are more likely to become the leader of their pack, suggesting that a brain-dwelling intruder encourages its host to take more risks.        </p><div>

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

It is estimated that between 30-50% of people worldwide are infected with the parasite, which remains for life as a latent tissue cyst. However, people with a healthy immune system rarely experience any symptoms.

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

The new study, published Thursday in the journal Communications Biology, drew on 26 years of data on gray wolves that live in Yellowstone National Park in the US to investigate how the parasite affects their behavior.

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

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

The study said that infected wolves were 11 times more likely to leave infected than wolves without parasites, indicating a higher risk rate.

The researchers estimate that an injured wolf is 46 times more likely to become the leader of the pack, adding that the role is usually taken over by more aggressive animals.

Kira Cassidy, a co-author of the study, told AFP that while being bold isn’t necessarily a bad thing, it can “reduce the survival of bolder animals because they may make decisions that put them in danger more often.”

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

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

Laboratory research has also found that rodents infected with the parasite lose their instinctive fear of cats — driving them into the hands of the only host in which T. gondii can breed.

William Sullivan, a professor of pharmacology and toxicology at Indiana University School of Medicine who has been studying chondriasis for more than 25 years, called Wolf Leaf a “rare gem.”

But he cautioned that such an observational study cannot show causation.

“A coyote born to risk may simply be more likely to venture into cougar territory and contract Toxoplasma,” he said.

“If the results are correct, they suggest that 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, “Nobody knows for sure and the literature is mixed.”

Ajay Vyas, a T. gondii expert at Singapore’s Nanyang Technological University, warns of the conclusion that infection can increase risk in people.

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

People often get toxoplasma gondii from eating undercooked meat — or via their pet cat, especially when cleaning 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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