Study: How a neuroparasite infection turns wolves into alpha animals

The parasite makes the leader of the pack
The infection gives the wolves a career boost

In a wolf pack, infection with the parasite determines who is more likely to become pack leader. Gray wolves who have had toxoplasmosis are more likely to become alphas, a US study shows.

Toxoplasmosis-infected gray wolves become pack leaders much more often than uninfected relatives. It is reported by American scientists in the journal “Communications Biology”. The neuroparasite probably makes the animals more aggressive, which could be an advantage in a battle for leadership. Wolves infected with the protozoan Toxoplasma gondii are 46 times more likely to become pack leaders.

In many animal species, such an infection is already known to significantly alter their typical behavior. Whether the neuroparasite causes behavioral changes in humans is still a matter of controversy. Among other things, studies report more reckless driving behavior among infected people, a greater desire to do business, and an association with pathological irritability. However, all these studies only show correlations, not causation.

For the current study, a team led by American biologists Connor Meyer and Kira Cassidy analyzed data on the behavior and distribution of gray wolves (Canis lupus) collected between 1995 and 2020 in Yellowstone National Park in the US state of Wyoming. In addition, they took blood samples from 229 anesthetized animals and tested them for antibodies against Toxoplasma gondii.

Advantage for the pathogen

Biologists have found that infected wolves behave more risky. On the one hand, this was reflected in a greater probability of leaving the pack earlier, both in males and in females. Behavior that makes sense with respect to pathogen spread: The pathogen is more likely to enter areas where it has not previously circulated. It has a similar effect when infected animals become pack leaders.

Toxoplasma gondii is widespread throughout the world wherever there are cats. The parasite produces eggs (oocytes) only in the cells of the cat’s intestinal lining. The eggs are shed in the cat’s feces and can cause infection after 1 to 5 days. Eggs in soil remain infective for months.

Healthy people usually do not notice anything at all about infection with the pathogen and remain without symptoms. If a person with a weakened immune system becomes ill, for example due to an organ transplant or HIV disease, toxoplasmosis infection can also lead to encephalitis.

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