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Great article on Toxoplasma in the NYT by Carl Zimmer. Apparently it hitches a ride on dendritic cells.

Scientists are now discovering some of the secrets of Toxoplasma’s success. Researchers in Sweden report that the parasite fans out through the body by manipulating mobile cells that are part of the immune system. Toxoplasma hijacks these so-called dendritic cells and makes them race around the body and ignore commands from other immune cells to commit suicide. The dendritic cells sneak the parasites into the brain and other organs, acting much like a Trojan horse.

[...]“That led us to think, what if this parasite is directing these [dendritic] cells to move and to disseminate through the body?” Dr. Barragan said. He and his colleagues put dendritic cells in a dish and injected them with Toxoplasma. They noticed that the parasites triggered a peculiar change: the dendritic cells became hyperactive, crawling for an entire day. [...] Injecting dendritic cells carrying Toxoplasma spread the parasites to the brain and other organs far faster than injecting Toxoplasma alone.

You can read the full paper by Miguel Tam and Mary Jo Wick in Cellular Microbiology.

Of note is a paper by reporting that malaria pigment “hemozoin” paralyzes dendritic cells (Urban, 2006). So is someone infected with malaria protected against Toxoplasma spread?

It’s exciting (and scary!) how little we really know about how diseases actually spread and cause symptoms. There are plenty of tricks used by bacteria, viruses, protozoa, and fungi to evade the immune system.

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