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<br /> A Common Parasite Reveals Its Strongest Asset: Stealth - New York Times Page i of 5 <br /> <br /> <br /> <br /> t5he cw Mork Omer ~A'NTER MENOLY FOROAT w <br /> SF]NSGREp BY <br /> (~Vtr(TIC_ .l, lJune 20, 2006 <br /> <br /> <br /> <br /> A Common Parasite Reveals Its Strongest Asset: <br /> <br /> Stealth <br /> <br /> By CARL ZIMMER <br /> Correetion Appended <br /> <br /> <br /> On paper, Toxoplasma gondii looks as if it ought to be the most famous parasite on earth. This <br /> single-celled pathogen infects over half the world's population, including an estimated 50 <br /> million Americans. Each of Toxoplasma's victims carries thousands of the parasites, many <br /> residing in the brain. As if that were not enough of an accomplishment, Toxoplasma is equally <br /> <br /> adept at infecting all other warm-blooded animals, as disparate as chickens and kangaroos. <br /> <br /> Scientists are now discovering some of the secrets of Toxoplasma's success. Researchers in <br /> Sweden report that the parasite fans out through the body by manipulating mobile cells that <br /> <br /> are part of the immune system. Toxoplasma hijacks these so-called dendritic cells and makes <br /> them race around the body and ignore commands from other immune cells to commit suicide. <br /> The dendritic cells sneak the parasites into the brain and other organs, acting much like a <br /> Trojan horse. <br /> <br /> <br /> Strategies like this one have made Toxoplasma incredibly widespread and incredibly obscure. <br /> Mention the parasite to most people and chances are you will draw a blank. Pathogens that <br /> infect far fewer people, like the Ebola and West Nile viruses, are far more famous. <br /> <br /> <br /> Toxoplasma's obscurity is in fact a great tribute to its powers. "To the parasite's credit, it's <br /> incredibly successful," said Dr. Uoyd Kasper of Dartmouth Medical School. "It's adapted itself <br /> to be a benign infection." <br /> <br /> For the vast majority of people, Toxoplasma causes no serious effects. It manages this feat by <br /> <br /> hijacking our cells and immune system, and establishing a careful harmony between parasite <br /> and host. "Once you get infected with Toxoplasma, you're infected for life," Dr. Kasper said. <br /> <br /> Toxoplasma can, however, cause serious brain damage in those with weak immune systems, <br /> <br /> like fetuses and adults with AIDS. <br /> <br /> <br /> http:/Iwww.nytimes.com/2006/06/20/science/20toxo.html?ei=5070&en=71bO423407od4... 11/14/2006 <br />