Researchers from the Harvard School of Public Health, Walter Reed ArmyInstitute of Research, and a team of collaborators have observed forthe first time that the risk of multiple sclerosis (MS) increases bymany folds following infection with the Epstein-Barr virus (EBV). Thisfinding implicates EBV as a contributory cause to multiple sclerosis.The study was published in an advance online edition of the journal Annalsof Neurology and will appear in a later print edition.Hundred of thousands of individuals not infected with EBV werefollowed up for several years through repeated blood samplescollections. Researchers were then able to determine the time whenindividuals developed an EBV infection and its relation to MS onset.“The recruitment of individuals before they were infected with EBV andfollowing up with them for several years is the critical methodologicalaspect that makes this study qualitatively different from all previouswork,” said AlbertoAscherio, senior author of the study and professor of epidemiologyand nutrition at Harvard School of Public Health and professor ofmedicine at Harvard Medical School.MS is a chronic degenerative disease of the central nervous system.Women are more likely than men to get the disease and it is the mostcommon neurologically disabling disease in young adults. Althoughgenetic predisposition plays an important role in determiningsusceptibility, past studies have shown that environmental factors areequally important.EBV is a herpes virus and one of the most common human virusesworldwide. Infection in early childhood is common and usuallyasymptomatic. Late age at infection, however, often causes infectiousmononucleosis. In the U.S., upwards of 95% of adults are infected withthe virus, but free of symptoms. EBV has been associated with some typesof cancer and can cause serious complications when the immune system issuppressed, for example, in transplant recipients. There is noeffective treatment for EBV.This is the first study based on the longitudinal follow-up ofseveral thousand individuals who were not infected with EBV at the timeof recruitment. The study population was made up of active-duty US Army,Navy, and Marines personnel who have at least one blood sample in theDepartment of Defense Serum Repository. The electronic databases of thePhysical Disability Agencies of the US Army and Navy were then searchedfor individuals whose records indicated a possible diagnosis of MSreported between 1992 and 2004.The researchers selected 305 individuals diagnosed with MS and whohad blood specimens collected before the date of their diagnosis. Twocontrols for each case were then selected from the serum database andmatched by branch of service, sex, date of blood collection, and age attime of blood collection.The study found that MS risk is extremely low amongindividuals not infected with EBV, but it increases sharply in the sameindividuals following EBV infection.“The observation that MS occurred only after EBV is a big stepforward,” said Alberto Ascherio. “Until now we knew that virtually allMS patients are infected with EBV, but we could not exclude twonon-causal explanations for this finding: that EBV infection is aconsequence rather than a cause of MS, and that individuals who are EBVnegative could be genetically resistant to MS. Both of theseexplanations are inconsistent with the present findings,” said Ascherio.“The evidence is now sufficiently compelling to justify theallocation of more resources to the development of interventionstargeting EBV infection, or the immune response to EBV infection, asthese may contribute to MS prevention,” he said.The study was supported by a grant from the National Institute ofNeurological Disorders and Stroke.