Quirks and Quarks·Quirks & Quarks

Parasite turns mice into mindless cat-fighting zombies by hijacking immune cells

The parasite makes mice fearless, so it will get eaten by a cat where the parasite can replicate.
How a cat parasite exploits immune cells in mice to reach its brain in order to exert mind control. (Pixabay)

The parasite's life cycle

Normally if a mouse sees a cat, it scuttles away in the other direction, but that's not what happens after mice get infected with a parasite called Toxoplasma gondii. Once inside the mouse's body, the parasite hijacks the mouse's immune system to move throughout the body and brain. The infected mouse then becomes fearless and almost starts taunting the cat — until it's eaten. The parasite uses this mind-control trick in mice because it can only replicate once it's inside a cat's gut. 

How the parasite hijacks the mouse's immune system

Scientists have now figured out exactly how the parasite hijacks the mouse's immune cells to get around the body to the brain. Dr. Antonio Barragan, a professor in the Department of Molecular Biosciences at Stockholm University in Sweden, is the senior author of the study that came out in PLOS Pathogens.

After a mouse ingests the parasite, it ends up in the stomach and intestine. From there it makes its way to the immune cells, which are supposed to be the gatekeepers of the immune system meant to kill invading parasites. Instead these parasites invades the immune cells and gives it orders to be used as a taxi.

The parasite does this in a very clever way. It enters the cells, lives inside in a little cocoon inside the cell. And from there, it starts to communicate with the cell.- Dr. Antonio Barragan from Stockholm University

"The parasite does this in a very clever way," says Barragan. "It enters the cells, lives inside in a little cocoon inside the cell. And from there, it starts to communicate with the cell." The message it sends is mediated by the small signaling molecule calcium.

"The parasite makes the cell produce also GABA, which is a neurotransmitter, and that triggers an activation — a whole system in the cell."

GABA is the spark that sends the calcium message, which activates the cell to move throughout the body and eventually to the brain. 

Why it's important

After the parasite replicates in the cat's intestine, its eggs can come out in the cat's feces, which can then get eaten up by any number of animals, such as a rodent or a cow. It's also an extremely common parasite in humans. We can catch it from cleaning cats' litter boxes or from eating raw meat. For the most part, it's harmless. It's only becomes life threatening in those with impaired immune systems and for unborn children, which is why pregnant women shouldn't clean litter boxes.

The Toxoplasma gondii parasite turns mice into fearless zombies, so they'll get eaten by a cat because the only place the parasite can replicate is in a cat's gut. (Pixabay)

Barragan says he hopes that by finding the mechanism of how the parasite moves around the mouse's body, scientists will learn how to design a new treatment to reduce spread.

In his experimental study, he did test a blood pressure medication, known to target calcium channels. "Indeed, that medicine had an effect on the spread of the parasite. But I should add that we don't claim this medicine is a way to cure toxoplasmosis, but we could prove at least that stopping the message from arriving from the parasite could impede the spread of the parasite."