Mind-altering parasite could make infected people more attractive, study suggests

(ORDO NEWS) — The brain addictive parasite Toxoplasma gondii seems to be almost everywhere. Up to 50 percent of humans are thought to be infected with this microscopic invader, and a number of studies show that it can alter the behavior of humans, as well as many other animals.

The parasite has been linked to a wide range of neurological disorders, including schizophrenia and psychotic episodes, and scientists continue to uncover more and more mysterious effects that can result from infection.

In one such new study, scientists found that men and women infected with the parasite were ultimately rated as more attractive and healthier than uninfected people.

At first glance, this may seem strange and unlikely. But hypothetically, this phenomenon may make sense from the point of view of evolutionary biology, the scientists say.

Mind altering parasite could make infected people more attractive study suggests 2
Composite images of 10 Toxoplasma infected women and men (a), next to 10 composite images of 10 uninfected women and men (b)

Amid the many neurobiological changes that T. gondii infection induces in its hosts, the researchers speculate that some of these changes may sometimes benefit infected animals – which may subsequently benefit the parasite, furthering its own transmission prospects.

“In one study, Toxoplasma-infected male rats were perceived as more sexually attractive and preferred as sexual partners by non-infected female rats,” the researchers explain in a new paper led by first author and biologist Javier Borras-Leon of the University of Turku in Finland.

Much research has been devoted to the study of whether similar effects are observed when infected with T. gondii in humans.

The evidence is far from clear, but some evidence suggests that infected men have higher testosterone levels than uninfected men.

It is possible that men with higher testosterone levels may be more prone to parasite infestation in the first place due to higher levels of risk-taking behavior associated with this hormone.

An alternative view, however, is that the parasite may be able to subtly alter its host’s phenotype by manipulating chemicals in the animal’s body, such as neurotransmitters and hormones, to achieve its own goals.

These changes could be far-reaching, suggest Borraz-Leon and his team.

“Some sexually transmitted parasites, such as T. gondii, can cause changes in the appearance and behavior of the human host, either as a by-product of the infection or as a result of the parasite’s manipulation to increase its spread to new hosts,” the researchers write.

To test this hypothesis, the researchers compared 35 people (22 men, 13 women) infected with T. gondii with 178 people (86 men, 92 women) who did not carry the parasite.

All participants (including those infected) were healthy college students who had previously been bled for another T. gondii study.

After running a number of different tests on participants, including interviews, physical measurements, and visual assessment, the researchers found that Toxoplasma-infected subjects had significantly lower fluctuating facial asymmetry than uninfected subjects.

Fluctuating asymmetry is a measure of deviation from symmetrical facial features, with lower levels of asymmetry (i.e., higher symmetry) associated with better physical health, good genes, and attractiveness, among other things.

In addition, parasite-carrying women were found to have lower body weight and BMI than uninfected women, and they reported both higher self-rated attractiveness and more sexual partners.

In a separate experiment, a group of 205 independent volunteers evaluated photographs of participants’ faces, and the experts concluded that infected participants looked significantly more attractive and healthier than uninfected ones.

Interpreting the findings, the researchers say it is possible that T. gondii infection may cause changes in the facial symmetry of its hosts through changes in endocrinological variables such as testosterone levels.

In addition, the parasite can influence the metabolic rate of hosts, pushing infected individuals to affect their health and perceived attractiveness.

However, all of this is just speculation so far, and the team acknowledges that other interpretations are possible, including the idea that highly symmetrical, attractive individuals might somehow better tolerate the physiological costs associated with parasitism, which are otherwise considered a burden on humans. health.

As to which interpretation is correct, it is impossible to say for sure based on this study alone, and the researchers acknowledge that the small sample size in their experiment is a limiting factor for statistical analysis.

For this reason, future studies with a larger number of participants will be required to confirm or refute their general hypothesis.

But maybe – just maybe, they say – this bewildered parasite is not necessarily our enemy.

“It is possible that the apparently non-pathological and potentially beneficial interactions between T. gondii and some of its intermediate hosts, such as rats and humans, are the result of coevolutionary strategies that benefit, or at least do not harm, both the parasite and owner,” the researchers write.


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