While it was discovered about 20 years ago that a parasitic infection could remove innate fear of predators from a mouse, it was recently discovered that this change is permanent, even after the parasite has been removed.
The Toxoplasma parasite can be deadly to immunocompromised humans and can cause spontaneous abortion in otherwise healthy pregnant women. The parasite is found in cat feces (which is why pregnant women are advised to avoid litter boxes). Its behavioral effects on a mouse brain, however, have lead some scientists to speculate that an infection may induce schizophrenia or suicidal behavior in humans.
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Credit: Wendy Ingram and Adrienne Greene