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Parasite Makes Rats Fearless in Front of Cats

Update Date: Sep 19, 2013 03:06 PM EDT
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Researchers have known that the toxoplasma parasite can be one deadly organism. Toxoplasma parasites are most commonly found in cats where they thrive. When the parasite infects pregnant women, it can immediately lead to a spontaneous abortion. When it infects patients with poor and compromised immune systems, it can lead to deaths. Even though this parasite can cause fatal results, a new study discovered that the toxoplasma parasite does something completely different to mice.

For this study, the researchers headed by graduate student Wendy Ingram from the University of California, Berkeley, examined the effects of the parasite once it infects mice. She used three strains of the parasite and compared the infected mice's behaviors to the behaviors of normal and healthy mice. She had tested the mice's response to bobcat urine and rabbit urine. Mice will generally avoid bobcat urine and do not react to rabbit urine. Ingram found that infected mice roamed the area with bobcat urine fearlessly whereas uninfected mice avoided the area.

The effects appeared to be permanent even after the mice had bounced back from the flu-like symptoms associated with the toxoplasma parasite infection. The researchers also found that the fearless behavior stayed at least four months after the parasite was cleared from the body. Ingram's findings were the results of a study that started three years ago.

"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 said according to the University's press release.

The lasting fearless behavior is detrimental to the mice because they become easy prey to cats. Once cats eat them, the parasite will reproduce in the cat's intestinal track and continue infecting other organisms. Even though Ingram could not identify the exact causes of the fearless behavior, she reasoned that the parasite could have destroyed the mice's ability to smell cat urine. Other possibilities could be that the parasite permanently damaged the brain cells responsible for learning and memory.

"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 according to ABC News. "Toxoplasma has done a phenomenal job of figuring out mammalian brains in order to enhance its transmission through a complicated life cycle."

Ingram is now investigating how the mouse's immune system fights the infection. The study was published in PLOS ONE.

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