Viruses and the Immune System
Most researchers now believe that MS is an auto-immune disease, i.e. one in which the body turns its immune system on its own tissues.
There is evidence that myelin is attacked by a type of white blood cell whose usual role is to destroy ‘invaders’ like bacteria and viruses. Somehow, these and other immune system cells seem to have become programmed to react to myelin as though it were a ‘foreign’ substance. This might be because some proteins in myelin are similar to those found in certain viruses, particularly measles, mumps and herpes simplex (the cold sore virus). Many people who go on to develop MS have had these viruses in childhood – but so have millions of others who never get MS.
Viruses may act as a trigger in people with an in-built susceptibility to MS. It is possible that there could be a specific ‘MS virus’, but researchers have been unable to isolate one, despite an intensive search. MS is not spread from one person to another. Even if MS occurs in two partners living together it is most unlikely that this is due to ‘cross infection’.