Toxoplasma gondii can infect any warm-blooded host but is especially associated with rodents for one reason: It can only sexually reproduce in the intestines of cats. The parasite solves this reproductive hurdle by causing any mice it infects to lose their aversion to cat urine, making them more likely to be eaten by cats.
While toxoplasmosis has been studied for more than a century, Wendy Ingram, Ph.D. candidate in molecular and cellular biology at UC Berkeley, and a team of researchers have uncovered intriguing new information behind this brain-bending parasite. According to their recent findings, the behavioral changes that occur once a mouse is infected persist for the duration of the animal’s life—even after the parasite is gone.
Although they have yet to identify the mechanism responsible for these changes, Ingram has a hunch. “There’s a growing body of research regarding a possible connection between your immune system and your neurobiology and behavior,” she says. In spite of preliminary data suggesting the involvement of an immune molecule, she is hesitant to make assumptions. “Often, nature’s imagination is greater than our own,” she says.
Once toxoplasmosis reproduces inside a cat, the parasite forms millions of oocysts that are then spread through contact with the cat’s feces, Ingram says. “Owning cats is a major risk factor for contracting toxo, especially outdoor cats,” she says.
Although up to one third of humans contract the parasite, a healthy immune system can usually render it harmless. Risk of serious complications is limited to people suffering from immunocompromising illnesses like HIV, or people on immunosuppressants such as organ transplant recipients. Pregnant women are also at risk because the virus can cross the placental barrier. “Fetuses don’t have a full immune system so they aren’t protected at all,” Ingram says. “It has been known to cause blindness, developmental issues, or even miscarriages.”
