Mice May Permanently Lose Fear of Cats Following Infection With Toxoplasma Parasite

Posted on September 19, 2013

Mouse infected with toxoplasma parasite visits a cat


Researchers have found that mice may permanently lose their fear of cats following an infection with the Toxoplasma parasite. In humans, the parasite can cause spontaneous abortion in pregnant women and death in immune-compromised patients. The infection does not directly kill mice, but it does cause them to lose their fear of cats, which could end up being deadly. A mouse infected with the parasite and unafraid of a cat is pictured above.

The research was conducted by graduate student Wendy Ingram at the University of California, Berkeley. She says the parasite 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.

Wendy Ingram discovered that the parasite's effect seems to be permanent. Her research found fearless behavior in mice persists long after the mouse recovers from the flu-like symptoms of toxoplasmosis, and for months after the parasitic infection is cleared from its body. While earlier studies showed mice lose their fear of bobcat urine for a few weeks after infection, Ingram showed that the three most common strains of Toxoplasma gondii make mice less fearful of cats for at least four months.

Ingram says in a press release, "Even when the parasite is cleared and it's 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 also says, "The idea that this parasite knows more about our brains than we do, and has the ability to exert desired change in complicated rodent behavior, is absolutely fascinating. Toxoplasma has done a phenomenal job of figuring out mammalian brains in order to enhance its transmission through a complicated life cycle."

The research was published here in the journal, PLoS ONE.

Photo: Wendy Ingram, UC Berkeley