Mice Lose their Fear of Cats After Being Infected with Brain Altering Parasite

Toxoplasma gondii- the cat parasite known to alter brain function in humans can make mice forget their fear of cats, a new study has reported.

It is already known that mice infected with a weak strain of the cat parasite become fearless. The new study, conducted by researchers at University of California, Berkeley, shows that mice infected with the parasite can permanently lose their fear of cats, even after they are cleared of the infection.

Cats seem to have mastered the art of mind-control. Getting mice infected with the parasite benefits both the cat and the parasite; the cat gets to eat a mouse that is foolishly bold and the parasite can again go back to living and reproducing in the cat's intestines.

Researchers speculate that the parasite may be damaging the mice's sense of smell or interfering with some other neuronal pathway.

"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," Wendy Ingram at the University of California, Berkeley, said.

Recently, many researchers have studied the effects of the parasite infection in humans. About a third of the world's population carries the parasite without showing any symptoms of the infections. A Danish study had reported that women who are exposed to the parasite "Toxoplasma gondii" are more prone to commit suicide. Another study from Sweden published in the journal PLOS One showed that the parasite alters the way the brain works by hijacking a key neurotransmitter called gamma-Aminobutyric acid or GABA.

For the present study, Ingram and colleagues infected a group of mice with T. gondii and observed its impact on the animals' behavior. They found that infected mice showed no fear response to bobcat urine. Previous research has shown that recently infected mice become fearless. Ingram's study further demonstrated that the effect of the parasite remained for as long as four months even after the infection was cleared.

Another hypothesis explaining the phenomenon is that the immune-system of the mice is the source of the behavioral changes after infection. Ingram said that she would carry out further tests to find out if it was true.

"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," Ingram said in a news release. "Toxoplasma has done a phenomenal job of figuring out mammalian brains in order to enhance its transmission through a complicated life cycle."

The study, "Mice Infected with Low-virulence Strains of Toxoplasma gondii Lose their Innate Aversion to Cat Urine, Even after Extensive Parasite Clearance", is published in the journal PLoS ONE.