Wednesday, December 07, 2022

Mind-altering parasite may make people more attractive, study finds

While disease usually may make us worse for wear, a cunning parasite makes its human carriers more physically desirable, a new study claims.

In experiments, volunteers looked at photos of people who had and hadn’t been infected with Toxoplasma gondii, the parasite that causes the disease toxoplasmosis.

The parasite spreads through exposure to infected cat faeces, as well as through contaminated food or sex with an infected person.

The study authors found that infected men and women were rated as appearing ‘healthier and more attractive’ than those not carrying the parasite.

It’s likely the clever parasite somehow manipulates our appearance to make us more sexually desirable, which in turn increases its risk of being transmitted to other humans, although researchers don’t known exactly how.

A Disease-Causing Parasite Known To Cause Psychiatric Symptoms Such As Hallucinations Can Make Infected People More Attractive, A Study Shows.  Here Shows Composite Images Of 10 Toxoplasma-Infected Women And 10 Toxoplasma-Infected Men (A), And 10 Non-Infected Women And Ten Non-Infected Men (B)

A disease-causing parasite known to cause psychiatric symptoms such as hallucinations can make infected people more attractive, a study shows. Here shows composite images of 10 toxoplasma-infected women and 10 toxoplasma-infected men (a), and 10 non-infected women and ten non-infected men (b)

Infected Men And Women Were Rated As Appearing 'Healthier And More Attractive' Than Those Not Carrying The Parasite, The Experts Found

Infected men and women were rated as appearing ‘healthier and more attractive’ than those not carrying the parasite, the experts found


Toxoplasma gondii (T. gondii) is a parasitic protozoan that causes toxoplasmosis.

It infects species of warm-blooded animals, including humans. Transmission routes include contact with cat feces, contaminated food or water, or sex with an infected person.

It can persist for long periods of time in the bodies of humans (and other animals), possibly even for a lifetime.

Of those who are infected however, very few have symptoms because a healthy person’s immune system usually keeps the parasite from causing illness.

However, pregnant women and individuals who have compromised immune systems should be cautious; for them, a Toxoplasma infection could cause serious health problems.

Source: Centers for Disease Control and Prevention

The study was led by Javier Borráz-León, a biologist at the University of Turku in Finland, and published in PeerJ.

‘Our results suggest that some sexually transmitted parasites, such as T. gondii, may produce changes in the appearance and behavior of the human host,’ say the team.

,[This is done] either as a by-product of the infection or as the result of the manipulation of the parasite to increase its spread to new hosts.’

Acute toxoplasmosis in adults has already been associated with psychiatric symptoms such as delusions and hallucinations.

In mice, toxoplasmosis has also been linked with a loss of fear of cats – a clever manipulation by the T. gondii parasite to increase the probability of transmission by way of ingestion by the feline.

Another study has shown male rats infected with T. gondii were preferred as sexual partners by non-infected female rats.

For this new study, the experts compared 35 men and women infected with T. gondii and 178 men and women who did not have the parasite.

As well as having their photos taken, various measures were taken to determine their overall health, including body mass index (BMI) and hand grip strength.

Other data collected included number of minor ailments, self-perceived attractiveness and number of sexual partners.

3D Rendering Of Toxoplasma Gondii, A Parasitic Protozoan That Causes The Disease Toxoplasmosis

3D rendering of Toxoplasma gondii, a parasitic protozoan that causes the disease toxoplasmosis


Toxoplasma gondii is usually spread to humans through contact with cat faeces, or by eating undercooked meat.

Most people who become infected with the parasite are not aware of it, and will not experience any major symptoms.

However, research indicates that T. gondii could increase your risk of developing glioma, an aggressive type of brain cancer.

Scientists found people who have glioma – a type of tumor that occurs in the brain and spinal cord – are more likely to have antibodies to T. gondii (indicating that they have had a previous infection) than a similar group that was cancer-free.

According to the researchers, this suggests that exposure to the parasite could increase your risk of aggressive brain tumors.

Another 205 people were then recruited to evaluate the attractiveness and perceived health of the infected and non-infected people in the photos.

Photos of the participants were also assessed by the researchers for facial fluctuating asymmetry – a measure of how symmetrical the face is. It’s thought high symmetry of the face is an indicator of beauty and good health.

Researchers found that infected men had lower facial fluctuating asymmetry, although no significant differences were found for the other health variables.

Infected women, meanwhile, had lower body mass, lower body mass index, a tendency for lower facial fluctuating asymmetry, higher self-perceived attractiveness and a higher number of sexual partners than non-infected ones.

Toxoplasma-infected subjects from both sexes were also rated as more attractive and healthier than non-infected ones.

Currently, the experts can only speculate how the parasite boosts our health and perceived attractiveness.

One theory is that T. gondii infection may produce changes in facial symmetry of its hosts through changes in the endocrine system – the collection of glands that produce hormones including testosterone.

Prior studies found toxoplasma-infected men have higher testosterone levels and toxoplasma-infected women have lower testosterone levels than non-infected people.

The researchers speculate that T. gondii may be specially adapted to ensure it does not inflict too many ‘physiological and energetic costs to their hosts’.

The authors say: ‘If parasites diminish a host’s attractiveness and health to such an extent that finding a potential mate becomes almost impossible and survival is heavily comprised, parasites can decrease their own odds to reproduce and pass to the next generation, especially if the parasites ‘ route includes sexual transmission.’

Further studies with larger sample sizes will have to be carried out to confirm their hypotheses, they add.

‘The results lay the foundation for future research on the manipulation of the human host by sexually transmitted pathogens and parasites,’ the team concludes.


Chronic infection with the parasite Toxoplasma gondii makes mice lose their innate, hard-wired fear of cats, effectively turning them into zombies.

Toxoplasma gondii, a parasitic eukaryote, is known to remove rodents’ fear of cats and make them more careless in their presence.

This increases the chances of being passed from the rodent to the cat, its definite host and ultimate destination.

The loss of their innate fear may persist after the parasite is no longer detectable in their brains

So initial infection may cause permanent changes in the rodents’ brains.

A 2013 study by the University of California, Berkeley, found the mind-controlling parasite is even more powerful than was first thought.

Wendy Ingram, a graduate student at the university, tested mice by seeing whether they avoided cat urine, which is normal behaviour, versus rabbit urine, to which mice don’t react.

While earlier studies showed that mice lose their fear of cat urine for a few weeks after infection, Ingram showed that the three most common strains of Toxoplasma gondii make mice less fearful of cats for at least four months.


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