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Common human parasite alters mouse brains permanently

Kathleen Blanchard's picture
A fascinating study shows a common parasite carried my millions permanently alters cat behavior.

Researchers have discovered something fascinating about the well-known, but little understood Toxoplasma parasite. When they infected mice with the parasite, the rodents lost all their fear of cats.

Researchers know how the infection can behave in humans, but only to a degree.

What are symptoms of Toxoplasmosis?

Toxoplasmosis is a condition caused by the parasite that is carried by more than 60 million men, women, and children in the United States, according to the U.S. Centers for Disease Control (CDC).

Only some people get sick from Toxoplasma gondii, including pregnant women and anyone with a compromised immune system.

The parasite can cause infection from cat feces, eating contaminated or undercooked meat, drinking contaminated water and from a blood transfusion or organ donation.

When toxoplasmosis does cause symptoms in healthy or non-pregnant individuals, they are usually mild and much like the flu. More serious symptoms include confusion, loss of balance and coordination, difficulty focusing and seizures.

Mothers' whose infants become infected during birth can experience severe eye or brain damage. The treatment is antibiotics.

When researchers for the newest study observed mice that were infected they noticed long-term behavior changes that persisted even after the parasite was removed.

Mental illness linked to parasite infection

Past studies have linked the parasite in humans with mental illness and the CDC says the ramifications of the parasitic infection have been neglected.

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Understanding more about the behavior of Toxoplasma has become a research focus.

Graduate student Wendy Ingram at the University of California, Berkeley who conducted the study published in the journal he journal PLOS ONE, speculated the parasite might wipe out smell, making mice unable to detect a cat’s urine odor.

Another possibility, Ingram said is it might wipe out a cat’s memory. Perhaps they forget that cats are their nemesis.

The scientists started their investigation three years ago when they tested mouse behavior when they were exposed to rabbit urine that the rodents would not normally react to and bobcat urine that should raise some cat hairs.

The researchers know Toxoplasma causes cysts in the brain that usually dormant but can sometimes reactivate. But this time they used a special strain that doesn’t cause brain cysts, nor cause chronic infection.

The study

From prior studies, the researchers knew common forms of the infection kept cats fearless of bobcat urine for at least four months

It turns out the same thing happened, which led Ingram to suspect the parasite does something to the host that persists even after Toxoplasma is eradicated.

"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 press release.

The next step is to try to understand how Toxoplasma alters mouse behavior in a way that makes them forget they need to fear for their lives around cats.

What the study means to humans isn't yet certain, but the finding could have implications for understanding how the infection might cause schizophrenia or other mental health disorders in humans. It also means there is still much to be learned about parasites and their behavior that infect millions of people each year.

Image credit: Free Bing Clipart