While disease can usually make us worse from weariness, a cunning parasite is making its human carriers more physically desirable, according to a new study.
In the experiments, volunteers looked at pictures of people who had and had not been infected with toxoplasma, the parasite that causes toxoplasmosis.
The parasite is spread through exposure to infected cat litter, 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 to be “healthier and more attractive” than those who did not carry the parasite.
It’s possible that the intelligent parasite somehow manipulates our appearance to make us more desirable for sex, which in turn increases the risk of passing it on to other humans, although researchers don’t know exactly how.
A study shows that a disease-causing parasite known to cause psychiatric symptoms such as hallucinations can make sufferers more attractive. Shown here are composite images of 10 toxoplasma-positive women and 10 toxoplasma-positive men (A), 10 uninfected women and 10 uninfected men (B).
Experts found that infected men and women were rated as appearing to be “healthier and more attractive” than those who did not carry the parasite.
What is Toxoplasma gondii?
Toxoplasma gondii (T. gondii) is a protozoan parasite that causes toxoplasmosis.
It infects species of warm-blooded animals, including humans. Modes of transmission include contact with cat feces, contaminated food or water, or sex with an infected person.
It can persist for long periods in the bodies of humans (and other animals), possibly even for life.
However, of those infected, very few develop symptoms because a healthy person’s immune system prevents the parasite from causing disease.
However, pregnant women and individuals with weakened immune systems should exercise caution; For them, toxoplasmosis infection can 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 is published in PeerJ.
“Our results suggest that some sexually transmitted parasites, such as T. gondii, may induce changes in the appearance and behavior of the human host,” the team says.
“[This is done] Either as a byproduct of infection or as a result of the parasite’s manipulation to increase its spread to new hosts.
Acute toxoplasmosis in adults has already been linked to psychiatric symptoms such as delusions and hallucinations.
In mice, toxoplasmosis has also been linked to a loss of feline fear—a clever manipulation by the T. gondii parasite to increase the likelihood of transmission via cat ingestion.
Another study showed that male rats infected with T. gondii are preferred by uninfected rats as sexual partners.
In this new study, experts compared 35 men and women infected with T. gondii and 178 men and women who did not have the parasite.
In addition to having their pictures taken, various measures were taken to determine their general health, including body mass index (BMI) and grip strength.
Other data collected included a number of minor illnesses, subjective attractiveness, and the number of sexual partners.
3D view of Toxoplasma toxoplasma, a protozoan parasite that causes toxoplasmosis
Toxoplasma gondii may increase the risk of brain cancer
Toxoplasma gondii usually spreads to humans through contact with cat feces, or by eating undercooked meat.
Most people who become infected with the parasite are not aware of it, and will not experience any significant symptoms.
However, research suggests that T. gondii can increase the risk of developing glioma, an aggressive type of brain cancer.
Scientists have found that people with gliomas — a type of tumor that occurs in the brain and spinal cord — are more likely to have antibodies to T. gondii (indicating they have had a previous infection) than a similar group that was free of cancer.
According to the researchers, this indicates that exposure to the parasite can increase the risk of developing aggressive brain tumors.
Then another 205 subjects were recruited to assess the attractiveness and health of the injured and uninjured subjects in the photographs.
The participants’ photographs were also evaluated by the researchers for fluctuating facial asymmetry – a measure of how symmetric a face is. High facial symmetry is believed to be an indicator of beauty and good health.
The researchers found that affected men had fluctuating facial asymmetry, although there were no significant differences for the other health variables.
Meanwhile, affected women had lower body mass, lower body mass index, a tendency to lower facial asymmetry, higher attractiveness for self-perception and a greater number of sexual partners compared to unaffected partners.
People with toxoplasmosis of both sexes were also rated as more attractive and healthy than those without.
For now, only experts can speculate how the parasite enhances our health and our perceived attractiveness.
One theory is that T. gondii infection may induce changes in the facial symmetry of its hosts through changes in the endocrine system – the group of glands that produce hormones including testosterone.
Previous studies have found that men with toxoplasmosis have higher levels of testosterone and that women with toxoplasmosis have lower levels of testosterone than uninfected people.
The researchers speculate that T. gondii may be specially adapted to ensure that it does not incur many “physiological and biological costs to their hosts.”
“If parasites reduce host attractiveness and health to such an extent that finding a potential mate becomes nearly impossible and surviving significantly, parasites can reduce their odds of reproducing and passing on to the next generation, especially if the parasites’ pathway includes sexual transmission,” the authors say. “.
They added that further studies with larger sample sizes would need to be conducted to confirm their hypotheses.
The team concluded, “The findings lay the foundation for future research into the manipulation of the human host by sexually transmitted pathogens and parasites.”
The parasite that turns mice into zombies: Toxoplasma gondii makes monkeys lose their fear of cats
Chronic infection with the parasite Toxoplasma gondii causes mice to lose their constant innate fear of cats, effectively turning them into zombies.
It is known that Toxoplasma gondii, a parasite of eukaryotes, removes the fear of rodents from cats and makes them even more careless in their presence.
This increases the chances of transmission from the rodent to the cat, its specific host and final destination.
Their innate fear loss may continue after the parasite becomes undetectable in their brains
So the initial infection may cause permanent changes in the brains of rodents.
A 2013 study by the University of California, Berkeley, found that the mind-controlling parasite is even more powerful than initially thought.
Wendy Ingram, a graduate student at the university, tested mice by seeing if they avoid cat urine, a normal behaviour, versus rabbit urine, which mice don’t react to.
While previous studies have shown that mice lose their fear of cat urine for a few weeks after infection, Ingram has shown that the three most common strains of Toxoplasma gondii make mice less afraid of cats for at least four months.