Epstein Barr Virus (EBV) has long been suspected as a possible cause for MS. Dr. John W. Lindsey at the University of Texas Health Science Center at Houston focuses his research on MS. In a study with one particular genotype of EBV, no relationship was found. To read the abstract, scroll down on the page.
Well, that's one down. I don't know how many more genotypes they have to eliminate before they find a relationship -- if there is a relationship to be found. Keep looking!