Instead researchers at the Harvard T. H. Chan School of Public Health and Harvard Medical School turned to what they call “an experiment of nature.” They used two decades of blood samples from more than 10 million young adults on active duty in the U.S. military (the samples were taken for routine HIV testing). About 5 percent of those individuals (several hundred thousand people) were negative for Epstein-Barr when they started military service, and 955 eventually developed MS. The researchers were able to compare the outcomes of those who were subsequently infected and those who were not. The results, published on September 13 in Science, show that the risk of multiple sclerosis increased 32-fold after infection with Epstein-Barr but not after infection with other viruses. “These findings cannot be explained by any known risk factor for MS and suggest EBV as the leading cause of MS,” the researchers wrote. In an accompanying commentary, immunologists William H. Robinson and Lawrence Steinman, both at Stanford University, wrote, “These findings provide compelling data that implicate EBV as the trigger for the development of MS.” Epidemiologist Alberto Ascherio, senior author of the new study, says, “The bottom line is almost: if you’re not infected with EBV, you don’t get MS. It’s rare to get such black-and-white results.”
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