Academic journal article The Science Teacher

Infection Renders Mice Fearless of Cats

Academic journal article The Science Teacher

Infection Renders Mice Fearless of Cats

Article excerpt

The Toxoplasma parasite can be deadly, causing spontaneous abortion in pregnant women or killing immune-compromised patients, but it has even stranger effects in mice.

Infected mice lose their fear of cats, which is good for both cats and the parasite, because the cat gets an easy meal and the parasite gets into the cat's intestinal track, the only place it can sexually reproduce and continue its cycle of infection.

New research by graduate student Wendy Ingram at the University of California, Berkeley, reveals a scary twist to this scenario: The parasite's effect seems to be permanent. The fearless behavior in mice persists long after the mouse recovers from the flulike symptoms of toxoplasmosis and for months after the parasitic infection is cleared from the body, according to research published in the journal PLOS ONE.

"Even when the parasite is no longer in the brains of the animals, some kind of permanent long-term behavior change has occurred, even though we don't know what the actual mechanism is," Ingram says. She speculated that the parasite could damage the smell center of the brain so that the odor of cat urine can't be detected. The parasite could also directly alter neurons involved in memory and learning, or it could trigger a damaging host response, as in many human autoimmune diseases.

Ingram became interested in the protozoan parasite, Toxoplasma gondii, after reading about its behavior-altering effects in mice and rats and possible implications for its common host, the domesticated cat, and even humans. One-third of people around the world have been infected with Toxoplasma and probably have dormant cysts in their brains. Kept in check by the body's immune system, these cysts sometimes revive in immune-compromised people, leading to death, and some preliminary studies suggest that chronic infection may be linked to schizophrenia or suicidal behavior. …

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