Many people with MS ask if their disease was caused by a virus or other infectious agent. Much research has focused on trying to answer this question.
Evidence Pointing to a Viral Cause for MS
It is tempting to speculate on a viral cause for MS for several reasons:
- Viruses are known to cause demyelinating disease in animals and humans. Demyelination (destruction of myelin, the fatty sheath the surrounds and insulates nerve fibers in the central nervous system) causes nerve impulses to be slowed or halted and produces the symptoms of MS.
- Data from epidemiological studies—those that analyze variations in geographical, socioeconomic, genetic, and other factors—suggest that exposure to an infectious agent may be involved in causing MS. Some viruses are known to have a long latency period between time of infection and appearance of clinical symptoms, as is thought to be the case in MS.
- Increased antibodies to many different viruses have been found in the blood and cerebrospinal fluid of people with MS. However, this does not necessarily represent disease-causing infection by these viruses. It is more likely to be the result of non-specific immune activation.
No Definitive Link of Any One Virus to MS
Although many different viruses have been studies as possible causes of MS, there has not yet been definitive proof to link any one virus to the autoimmune reaction that is believed to be responsible for the demyelination seen in MS. At one time or another, canine distemper virus, measles virus, herpes virus (HHV-6), rubella (or German measles) virus, HTLV-1 virus, and others have been reported to be associated with MS. With the exception of HHV-6, later studies have not substantiated these reports, and there is no proof that any of them causes MS.
Looking at the Epstein-Barr Virus (EBV)
Several studies have suggested the Epstein-Barr virus as a possible culprit.
- In 2003, a study published in the Journal of the American Medical Association suggested that increased levels of immune antibodies that fight Epstein-Barr Virus (EBV)—the very common virus that causes infectious mononucleosis and other disorders—may be associated with an increased risk of developing MS. Although no causal relationship was established between EBV and multiple sclerosis, the researchers found that in spite of the fact that virtually all of the study participants, with and without MS, had early exposure to this virus, the antibodies to EBV were consistently higher in those individuals who subsequently developed MS than in the control group that did not develop MS. Furthermore, the risk of developing MS increased with increasing levels of antibodies, which were subsequently found to increase with age.
- In 2006, investigators reported that individuals who showed signs of significant exposure to the Epstein-Barr virus were twice as likely to develop MS up to 20 years later. While this study, funded in part by a pilot research grant from the National MS Society, added more evidence linking the virus to the risk of developing MS, it still did not prove that EBV actually causes MS.
- In 2007, investigators reported finding traces of Epstein-Barr virus in postmortem brains examined from people with different forms of MS. They found traces of EBV infection in immune cells (B cells and plasma cells) that had infiltrated 21 out of 22 brains from people with MS, but not in brains from people who had other neurological diseases that, like MS, involve inflammation. If these exciting findings are confirmed by other laboratories, they will add to growing evidence of a link between EBV and MS.
In spite of these findings, however, it is still not possible to determine whether EBV causes MS, or whether its presence is a consequence of MS.
MS is not Contagious
Currently, there is no evidence at all to suggest that MS is infectious or contagious. The role of a virus or viruses, if there is one, affects only people with a genetic predisposition to develop MS.