Parasite Renders Women More Promiscuous, Men Less Desirable

Last week you might have read about how a parasite found in cat poop "brainwashes" mice and rats into loving the one thing that should send them scurrying: the urine of their Archnemesis, the Cat (see article about that below). Now it seems that this parasite does some odd things to humans, too. From the University of California, San Francisco:


Fatal Attraction: Parasite Renders Women More Promiscuous, Men Less Desirable
By Stephanie Chang
Staff Writer

Toxoplasma gondii, commonly thought to be a relatively benign parasite, is transmitted to humans through the ingestion of infected cat feces or undercooked meat, and may significantly affect the behavior of infected individuals in a gender-specific manner.

Although approximately 2.5 billion people (roughly 40% of the world’s population) are estimated to be infected with T. gondii, the parasite typically remains contained by a healthy immune system and takes up permanent residence in the brains and musculature of infected individuals in the form of inactive cysts.

No treatment exists for these cysts, but the parasite is usually only considered a danger to pregnant women or immunocompromised patients. Infection with T. gondii has also been correlated with higher incidences of schizophrenia. However, recent data suggests that latent infection with T. gondii causes even more far-reaching and subtle behavioral effects.

According to an article written by Dr. Nicky Boulter in the December 2006 issue of Australasian Science, "infected men have been shown to have lower IQs, achieve a lower level of education and have shorter attention spans. They are also more likely to break rules and take risks, be more independent, more anti-social, suspicious, jealous and morose and are deemed to be less attractive to women. On the other hand, infected women tend to be more out-going, friendly, more promiscuous and are seen as being more attractive to men compared with non-infected controls."

The most compelling study conducted by Lindova et al. examined the behavior of 92 male students and 171 female students at a university in the Czech Republic. Participants consented to serological testing to assess the presence of anti-Toxoplasma antibodies, completed an extensive personality survey, and participated in a one-hour double-blind experiment conducted by the same female moderator. The moderator scored participants on every aspect of the interview, such as punctuality, responses to questions assessing social networks, personal appearance and clothing (on a 1-5 scale), willingness to drink a mystery substance (under the false premise of assessing the ability to taste a bitter compound), and willingness to be photographed. While infected males achieved significantly lower scores in areas of "Relationships," "Self-Control," and "Clothes Tidiness" compared to uninfected men, infected females were more likely to exhibit higher scores in these areas than their uninfected counterparts.

A similar trend in behavioral changes has been observed in mice infected by T. gondii according to studies conducted by Berdoy et al. Infected and uninfected mice were placed in boxes containing four areas containing distinct scents: mouse urine, neutral straw, rabbit urine, and cat urine. Infected mice were significantly more likely to spend more time loitering around the area scented with cat urine than uninfected mice. The authors postulate that this behavioral change leads to increased feline predation of infected mice, allowing the parasite T. gondii to complete its reproductive cycle in the cat.

Although the parasite’s effect on infected mice may be explained in this manner, it becomes less clear why T. gondii would benefit from the behavioral changes observed in infected humans, or why men and women may be affected differently. Lindova et al. suggests an intriguing theory to explain the difference in gender-based outcomes, proposing that infected males who exhibited risk-taking and antisocial behavior in a pre-civilized era would become more vulnerable to predation (perhaps by lions and tigers, no bears), allowing the parasite to spread. On the other hand, infected women who behave in a more outgoing, social, and promiscuous manner would have a higher likelihood of mating and passing on the parasite to their offspring.

Stephanie Chang is a first-year medical student.

From National Geographic:


Parasite "Brainwashes" Rats Into Craving Cat Urine, Study Finds
Ben Harder
for National Geographic News
April 3, 2007

The parasite Toxoplasma gondii uses a remarkable trick to spread from rodents to cats: It alters the brains of infected rats and mice so that they become attracted to—rather than repelled by—the scent of their predators.

A new study reveals that rodents infected with the parasitic protozoa are drawn to the smell of cat urine, apparently having lost their otherwise natural aversion to the scent. 
The parasite can only sexually reproduce in the feline gut, so it's advantageous for it to get from a rodent into a cat—if necessary, by helping the latter eat the former. 
In rodents, "brain circuits for many behaviors overlap with the brain circuits responsible for fear," said Ajai Vyas of Stanford University, who led the new study. 
"One would thus assume that if something messes up fear of cat pee, it will also mess up a variety of related behaviors." 
But Vyas's experiments showed that not to be the case. 
In fact, his test demonstrated just how precise and efficient the mind-bending parasite is. While manipulating rodents' innate fear of felines, T. gondii leaves other behaviors intact.
Toxoplasma-infected mice and rats retained most typical rodent phobias, including fears of dog odors, strange-smelling foods, and open spaces. Infected rodents also didn't appear to be sick. 
Only the animals' response to cats was abnormal: Uninfected rodents avoided an area of a room that researchers had scented with cat urine. But infected rodents actually seemed drawn to the smell. 
"Toxoplasma affects fear of cat odors with almost surgical precision," Vyas concluded. "A large number of other behaviors remain intact." 
"Brainwashing" Parasites 
"There are a million examples of parasites manipulating host behavior," said Robert Sapolsky, a Stanford University neuroscientist who collaborated with Vyas. 

In most cases, he said, "they do something terribly unsubtle, like destroying the vision, so [infected animals] are much less capable of avoiding predators." 
T. gondii, by contrast, "is not just sledge-hammering a behavior out of existence," Sapolsky said. 
"It's extinguishing a normal behavior"—avoidance of cats—"and replacing it with this incredibly maladaptive opposite." 
Vyas's team found that Toxoplasma, which forms cysts in the brain, tends to concentrate in an area of the brain called the amygdala. 
Because that region is linked to fear and anxiety, the finding provides a new clue to how the parasite manipulates behavior. 
Sapolsky, Vyas, and their colleagues reported their findings Monday in the Proceedings of the National Academy of Sciences. 
Manuel Berdoy, a zoologist at Oxford University in England, called the new finding "a delight." 
He and Joanne Webster, a researcher at Imperial College London, had previously found that Toxoplasma-infected rodents gravitated toward cat odors. 
The new study advances scientists' understanding of how the parasite pulls off the trick, Berdoy said. 
He called it "astonishing that [T. gondii] may be able to target specifically the neural pathways responsible for processing cat odors. 
"It's incredible that the parasite would be able to alter a response—cat aversion—that is so ingrained in the rats' psyche," Berdoy said.

Quote:Stephanie Chang is a first-year medical student.

Snacking at the kitty-litter box... yummy.

Tell me how a bacterium decides to modify the host's behavior to make it more likely to spread.  I suppose it "evolved" that ability?

I've been really curious about this particular bug.  I read somewhere that in France pregnant women who test positive are urged to abort asap.

Is it really a huge problem?  What if you're preggers and you have cats?  Do you have to kick them out of the house or what?
miss_fluffy Wrote:Is it really a huge problem? What if you're preggers and you have cats? Do you have to kick them out of the house or what?

There are other ways to come in contact with T. gondii ... but cat owners do have a slightly increased risk.

Most cat owners have already been exposed before pregnancy and have some level of immunity.  But it is suggested that pregnant women not sift or change their pets' litter boxes.  And if they must do so they often suggest wearing a particle mask and disposable gloves.

And of course the average indoor only house cat is not generally infected with T. gondii.  Which is why one of the bits of medical advice for pregnant cat owners is "don't let your indoor cat go outside."

For me pregnancy was the gold standard excuse to get out of litter box duty! :D

A quick Q & A about toxoplasmosis and pregnancy.
A substance that renders women more promiscuous and men less desirable?

It's called ALCOHOL. Old news......

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