Toxoplasma gondii is in the news again. It is a really interesting brain parasite. It lives in the guts of cats. Eggs are shedded with excrement, and inhaled by animals that are eaten by cats, e.g. mice and rats. T. gondii then form cysts in their brains. And here is the clever part. When a mouse or rat is infected, it is no longer afraid of the smell of cats, and it is therefore more likely to be caught and eaten.
Toxoplasma also infects people, and therefore pregnant women are adviced not to handle cats or cat litter.
Now an article in the Guardian reports that pregnant women with high levels of infection by the T. gondii parasite are more likely to give birth to boys. The parasite infects around 15% of Britons, but up to 80% of the population in some countries. Women whose antibody count is high – suggesting a substantial infection – has a much higher chance of having baby boys. In most populations the birth rate is around 51% boys, but women infected with toxoplasma had up to a 72% chance of a boy.