[Is multiple sclerosis a disease of viral origin?].

MS is a multifactorial disease in which host genetic factors as well as environmental factors may interact. Among them, the role of viruses is still debated since none has been directly or indirectly involved in the disease up to now. The latest candidates are HHV6 and MSRV. Recently, HHV6 antigens have been found in MS brain, but these results require further investigation. MSRV is a retroviral sequence isolated from MS tissue and it belongs to the already known ERV9 family of endogenous retroviruses. Its role in MS is only putative. To conclude, "MS virus" is still unidentified. Nevertheless, the search for a virus in MS should be pursued. In that perspective, animal models illustrate how host immune system interacts with viruses to lead to demyelination, a common feature of a multi-step process of diverse origins.