This Review aims to (1) explore EBV-related risk factors for MS, such as the timing of infection, genetic predisposition (for example, HLA-DRB1*15:01), environmental influences (for example, vitamin D levels) and CD8+ T cell response; and (2) to develop and refine virus-induced NHP models of MS. This evidence concerns the gene HLA-DRB1 and myeloid sarcoma.