Multiple sclerosis is caused by a complex interaction between genetic 
predisposition and environmental factors. Epstein-Barr virus (EBV) is an 
environmental risk factor that is strongly related to multiple sclerosis (MS), 
since EBV seropositivity is linked to a significant risk of developing MS. EBV 
may be involved in the pathogenesis of the disease and it is possibly a 
prerequisite for the development of MS. EBV infection persists in B-cells during 
the lifetime of the host and can modulate their function. In addition, MS 
patients might have a deficient capacity to eliminate latent EBV infection in 
the central nervous system and this would promote the accumulation of infected B 
cells. Several mechanisms of pathogenesis, including a direct and indirect 
function of infected B cells, have been postulated in inflammation and 
neurodegeneration. A relationship between EBV and human endogenous retroviruses 
in the pathogenesis of MS has also been reported. If EBV is important in the 
pathogenesis of MS, different therapeutic strategies seem possible for MS 
treatment.