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Boy-Friendly Parasite

November 6, 2006

A latent parasitic infection may make a pregnant woman much more likely to have a boy.


How a parasite may protect baby boys. I’m Bob Hirshon and this is Science Update.

Pregnant women who carry a common parasite called Toxoplasma may be 50 percent more likely to have a boy than a girl. This according to a new analysis of over eighteen hundred births, led by biologist Jaroslav Flegr of Charles University in the Czech Republic.

Why? Flegr explains that in general, women conceive far more male embryos than female. But because the mother’s immune system perceives male embryos as slightly foreign, many of these potential boys are miscarried. However, a chronic, dormant Toxoplasma infection can suppress the mother’s immune system.

JAROSLAV FLEGR (Charles University, Czech Republic):
And when there is some immunosuppression, for example this immunosuppression induced by Toxoplasma, much more males survive.

Since the infection is very common, it may be a factor in the worldwide sex ratio. I’m Bob Hirshon, for AAAS, the science society.