‘Crazy cat lady’ parasite makes mice less afraid and afraid of threats

The mind-expanding ‘crazy cat lady parasite’ who thought that mice should lose their fear of cats, actually makes them less anxious and risk-avoiding in general, according to a study.

Researchers from Switzerland studied the behavior of infected mice and discovered that they were more willing to investigate, interact with people and investigate animal odors.

They mapped the parasites-filled cysts in the mice’s brains and discovered that they also occur in the largest numbers in areas related to the processing of visual information.

The degree of behavioral change induced by the parasite infections also appears to be associated with levels of inflammation in nerve tissues.

However, the team emphasizes that people infected with the common parasite would never experience such high levels of neuro-inflammation.

People are not at risk for the so-called ‘crazy cat lady’ syndrome, she added – previous studies have not found that the infection increases the risk of subsequent psychological problems.

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The mind-expanding 'crazy cat lady parasite' that is thought to be mice losing their fear of cats, generally makes them less anxious and risk-averse, a study found

The mind-expanding ‘crazy cat lady parasite’ that is thought to be mice losing their fear of cats, generally makes them less anxious and risk-averse, a study found

Toxoplasma gondii is a single-celled parasite that can infect most warm-blooded species – including humans – and cause toxoplasmosis.

It is only known to reproduce sexually in cats.

In rodents, the infection is known to cause a phenomenon known as “fatal cat-like attraction” – a reduced aversion to cat odors that makes it easier for mice and rats to be caught by their cat-like predators.

When cats eat infected prey, the parasite passes into their feces, from which it can infect other hosts and continue to spread and multiply.

“T. gondii has served as a textbook example for a parasitic adaptive manipulation for 20 years, mainly because of the specificity of this manipulation,” said paper author and neurogeneticist Ivan Rodriguez of the University of Geneva

“We now show that behavioral change not only affects fear of feline predators, but that major changes occur in the brains of infected mice – which affect different behaviors and neural function in general.”

Professor Rodriguez and colleagues investigated the molecular mechanisms by which T. gondii can manipulate rodent behavior and first infected mice with the parasite and observed their behavior for five to ten weeks in different scenarios.

The team discovered that mice carrying the parasite were not only less afraid of feline predators, but in general seemed to be less anxious.

For example, infected mice spent more time in the open parts of a raised maze with both exposed and enclosed parts, and also showed a greater tendency to explore new environments and objects.

Faced with a potential threat – a hand from one of the researchers – the infected mice also wanted to interact by hand instead of avoiding defensive, defensive and fear-based behavior from their uninfected counterparts.

“Taken together, these findings suggest that chronic T. gondii infection reduces anxiety and risk aversion while increasing curiosity and exploratory behavior,” said co-author of the University of Geneva paper and neurogeneticist Madlaina Boillat.

Researchers studied the behavior of infected mice and discovered that they were more willing to explore people, interact with people and investigate the smells of other animals

Researchers studied the behavior of infected mice and discovered that they were more willing to explore people, interact with people and investigate the smells of other animals

Researchers studied the behavior of infected mice and discovered that they were more willing to explore people, interact with people and investigate the smells of other animals

In a second series of experiments, the team exposed both infected and uninfected mice to bobcat (photo), fox, and guinea pig urine. Although the team discovered that the infected mice were attracted to examine the bobcat urine - unlike mice that did not carry the parasite - they also appeared to be equally atypically interested in smelling the fox and caviar smells

In a second series of experiments, the team exposed both infected and uninfected mice to bobcat (photo), fox, and guinea pig urine. Although the team found that the infected mice were attracted to examine the bobcat urine - unlike mice that didn't carry the parasite - they also turned out to be equally atypically interested in smelling the fox and caviar smells

In a second series of experiments, the team exposed both infected and uninfected mice to bobcat, fox and guinea pigs (photo). Although the team found that the infected mice were attracted to examine the bobcat urine - unlike mice that didn't carry the parasite - they also turned out to be equally atypically interested in smelling the fox and caviar smells

In a second series of experiments, the team exposed both infected and uninfected mice to bobcat, fox and guinea pigs (photo). Although the team discovered that the infected mice were attracted to examine the bobcat urine - unlike mice that did not carry the parasite - they also appeared to be equally atypically interested in smelling the fox and caviar smells

In a second series of experiments, the team exposed both infected and uninfected mice to bobcat (left), fox and guinea pig (right) urine. Although the team discovered that the infected mice were attracted to examine the bobcat urine – unlike mice that did not carry the parasite – they also appeared to be equally atypically interested in smelling the fox and caviar smells

In a second series of experiments, the team exposed both infected and uninfected mice to bobcat, fox, and guinea pig urine.

Although the team discovered that the infected mice were attracted to examine the bobcat urine – unlike mice that did not carry the parasite – they also appeared to be equally atypically interested in smelling the fox and guinea pig scents.

This suggests that the parasite reduces the fear of the mice for all animals – cats, predators and non-predators such as guinea pigs.

Infected mice also appeared not to freeze when they saw a stunned rat – instead they bravely walked over it.

“These results contrast with the prevailing idea that the manipulation of the parasite by host behavior is specifically aimed at neural circuits that respond to feline predators,” said the paper author and microbiologist of the University of Geneva, Pierre-Mehdi Hammoudi.

The team found more of the parasite-filled cysts in the outer layers of the mice's brain - the so-called cerebral cortex - with the highest concentration found in those regions involved in processing visual information

The team found more of the parasite-filled cysts in the outer layers of the mice's brain - the so-called cerebral cortex - with the highest concentration found in those regions involved in processing visual information

The team found more of the parasite-filled cysts in the outer layers of the mice’s brain – the so-called cerebral cortex – with the highest concentration found in those regions involved in processing visual information

To find out the essence of what T. gondii does exactly with rodent brains, the team has investigated and mapped cysts in the brains of mice 10-12 weeks after infection with T. gondii.

Cysts appeared to appear in the brain, which the researchers suggest is a random process of infection and spread.

However, the team found more of parasite-filled cysts in the outer brain layers – the so-called cerebral cortex – with the highest concentration in those regions involved in processing visual information.

The severity of the behavioral changes induced by parasites was also found to be associated with the level of T. gondii load in the cysts and the levels of corresponding inflammation of the nerve tissue.

“Taken together, the findings point to behavioral manipulation mediated by neuronal inflammation rather than direct interference from the parasite itself with specific neuronal populations,” says Professor Rodriguez.

‘It’s not a simple on / off system. In the future, therefore, the level of chronic infections should always be taken into account when studying the effects of T. gondii on the host, “he added.

WHAT IS TOXOPLASMA GONDII?

Pictured, T. gondii parasites that live in a tissue cyst in the brain of a mouse, as seen under a microscope via florescence

Pictured, T. gondii parasites that live in a tissue cyst in the brain of a mouse, as seen under a microscope via florescence

Pictured, T. gondii parasites that live in a tissue cyst in the brain of a mouse, as seen under a microscope via florescence

T. gondii cannot be caught directly from cats and does not cause symptoms in most cases

T. gondii cannot be caught directly from cats and does not cause symptoms in most cases

T. gondii cannot be caught directly from cats and does not cause symptoms in most cases

Toxoplasma gondii is a single-celled parasite that can infect most warm-blooded species.

It is estimated that almost a third of the world’s population carries the long-term parasite.

It is only known to reproduce sexually in cats.

In rodents, the infection is known to cause a phenomenon known as “fatal cat-like attraction” – a reduced aversion to cat odors that makes it easier for mice and rats to be caught by their cat-like predators.

When cats eat infected prey, the parasite passes into their feces, from which it can infect other hosts and continue to spread and multiply.

The parasite is often caught from uncooked food, but can be spread through cat litter – however, it cannot be caught directly from cats.

T. gondii can cause toxoplasmosis – although this does not cause symptoms in most adults.

However, some people may experience flu-like symptoms for weeks or months.

Toxoplasmosis can be severe in people with a compromised immune system – such as people infected with HIV – and for the pregnant woman, because the disease can lead to fetal death.

That is why pregnant women are not advised to empty litter boxes.

T. gondii has become notorious for the so-called ‘crazy cat lady syndrome’ – a proposed association between the parasite and various mental disorders.

However, several studies have not found that early infection with the parasite increases the risk of developing mental illness later in life.

With their first study completed, the researchers are now investigating in more detail how inflammation can change behavioral characteristics such as anxiety, curiosity and socializing.

However, the researchers have emphasized that their results in mice may not be perfectly translated to humans – who generally exhibit fewer symptoms than rodents when infected with the parasite.

“We hope that people understand that they will not get the ‘crazy cat lady syndrome’ if they are infected with T. gondii,” said the paper author and microbiologist of the University of Geneva, Dominique Soldati-Favre.

“Although it seems that subtle behavioral changes can occur in humans, inflammation in the human brain may never reach the same level as in laboratory-infected mice.”

The full findings of the study were published in the journal Cell Reports.

However, the researchers have stressed that their results in mice may not be perfectly translated to humans - who generally exhibit fewer symptoms than rodents when infected with the parasite

However, the researchers have stressed that their results in mice may not be perfectly translated to humans - who generally exhibit fewer symptoms than rodents when infected with the parasite

However, the researchers have stressed that their results in mice may not be perfectly translated to humans – who generally exhibit fewer symptoms than rodents when infected with the parasite

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