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Nearly a third of people around the world are infected with the parasite Toxoplasma gondii. The infection is often asymptomatic, but can be incredibly dangerous for people with weak immune systems or babies in utero. Now, scientists have figured out the mechanism that allows the parasite to pass the blood-brain barrier. Here’s what lead researcher and pathobiologist Christopher Hunter of University of Pennsylvania said about the findings, published in the latest Nature Microbiology.

What do we know about how parasites cross into the brain?

Many pathogens get into the brain. For some, like rabies, the pathogen comes up through neurons. But for many other pathogens, we don’t understand how this really works. One way is a Trojan horse mechanism, where a parasite infects a cell and the cell carries it into the brain. It’s a lovely mechanism, beloved by microbiologists. There are other mechanisms by which the parasite migrates between cells into the brain.

And what did you find out about how Toxoplasma gondii gets into the brain?

The parasite is found in the blood, which we didn’t really know. It has to do with the endothelial cells, which are like the pavement on a road that line the blood vessels. The parasite infects those endothelial cells and reproduces in them. Those cells then kind of just move into the next cell, and the next cell is on the other side of the blood brain barrier. If there was no blood brain barrier perhaps more parasites might get in.


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