[Reading Science] Parasites Manipulating Hosts... Are You Also a Victim?

US Montana University Research Team Publishes Study on Ecology of Wolves Infected with Toxoplasma gondii
"Much Higher Probability of Becoming Leader or Independent," "Evidence of Significant Impact on Ecosystem"
One-Third of Humans Chronically Infected... Become Reckless and Brave, '2.6 Times More Traffic Accidents'

*Reference photo - Appearance of Yeongasi (Source: National Institute of Environmental Research)

[Asia Economy Reporter Kim Bong-su] The 2012 film "Yeongasi" sparked a nationwide craze for deworming medication with its premise that parasites infecting the human body control the host's behavior, causing drowning. However, a study from the United States has revealed that wolves infected with a specific parasite become braver and more resilient, often becoming leaders of their packs, showing clear behavioral changes.

According to the international journal Nature on the 26th, a research team from the University of Montana in the U.S. published these findings on the 24th (local time) in the biological science journal Communications Biology. The team focused on wolves infected with Toxoplasma gondii, a parasite for which cats are the definitive host. The researchers conducted a long-term study over approximately 27 years on wolves living in Yellowstone National Park. These wolves often become infected with Toxoplasma gondii by preying on cougars, a type of cat, or through their feces.

The research team collected 256 serum samples from 229 wolves and observed their behavioral traits, social status, and how they lived within their groups. The results showed that wolves infected with Toxoplasma gondii were 46 times more likely to become pack leaders than uninfected wolves. They were also 11 times more likely to leave their family and form new packs.

Regarding these findings, the research team highlighted the influence of Toxoplasma gondii. This parasite is mainly found in wild animals but can also infect humans, and it is known to make hosts behave recklessly and bravely. In other words, this parasite reproduces sexually inside cats and manipulates the host’s behavior to return to the cat’s body. In the case of mice, it makes them unafraid of cats and even strongly attracted to cat urine. It forms cysts in the host’s brain region, where it secretes specific substances that affect the nervous system.

Wolves infected with this parasite exhibited aggressive and risk-taking tendencies. This behavior is suitable for exploring new breeding grounds for the wolf pack or protecting the pack from enemies. Even in humans, infection with this parasite has been linked to increased secretion of testosterone and dopamine, leading to 2.6 times more traffic accidents and associations with psychiatric phenomena such as suicide and schizophrenia. It is estimated that about one-third of the global population is chronically infected.

Dan McNulty, a biology professor at Utah State University, said, "This study provides compelling evidence that (Toxoplasma gondii) infection has a significant impact on the behavior and ecology of wild animal populations." Connor Meyer, a biology professor at the University of Montana who led the research, explained, "The significance of this study is that parasites may have had a much greater impact on entire ecosystems than previously thought."