Parasite makes men dumb, women sexy

December 26, 2006 - 5:33PM

A common parasite can increase a women's attractiveness to the opposite sex but also make men more stupid, an Australian researcher says.

About 40 per cent of the world's population is infected with Toxoplasma gondii, including about eight million Australians.

Human infection generally occurs when people eat raw or undercooked meat that has cysts containing the parasite, or accidentally ingest some of the parasite's eggs excreted by an infected cat.

The parasite is known to be dangerous to pregnant women as it can cause disability or abortion of the unborn child, and can also kill people whose immune systems are weakened.

Until recently it was thought to be an insignificant disease in healthy people, Sydney University of Technology infectious disease researcher Nicky Boulter said, but new research has revealed its mind-altering properties.

"Interestingly, the effect of infection is different between men and women," Dr Boulter writes in the latest issue of Australasian Science magazine.

"Infected men 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 less attractive to women.

"On the other hand, infected women tend to be more outgoing, friendly, more promiscuous, and are considered more attractive to men compared with non-infected controls.

"In short, it can make men behave like alley cats and women behave like sex kittens".

[...]

Rats and mice normally flee if they smell cat urine, but not if they're infected by the protozoan parasite Toxoplasma gondii. The parasite can only complete its life cycle if its rodent host is eaten by a cat, so it "brainwashes" the creature into apparently liking the scent.

Now Ajai Vyas and his colleagues at Stanford University in California, US, have revealed that the brainwashing is surgically precise. The parasites seem to reverse the rodent's innate fear by interfering with the amygdala, the seat of conditioned responses in the brain. Vyas's team looked at the distribution of the parasite in the brain of infected rats, and found it was almost twice as dense in the amygdala.

The exquisite precision leaves intact all other neurological mechanisms for learning to avoid danger, so the rodents learn to survive all hazards except being eaten by cats \ufffd the only form of death beneficial to the parasite.

Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.0608310104)