Could an Ancient Virus Cause MS?

One of the infuriating things about MS is we still don’t know what causes it. The problem is there doesn’t appear to be any one single trigger for MS. We know genes are involved (you’re more likely to get MS if you have family members with the disease, for example) but that’s not the whole story. Because we also know that if one identical twin has MS, the other twin only has a one in four chance of developing the disease – despite having near identical genes. For this reason, scientists have come to the conclusion that environmental factors (i.e. something outside the body) may be involved in triggering MS.

One of many theories is that the environmental trigger could be a virus. This is based on the finding that 90–95% of people with MS have immune proteins in their spinal fluid, the kind seen in people with nervous system diseases caused by viruses.

The Epstein–Barr Virus

One of the viruses scientists have been looking into is the Epstein–Barr virus (EBV). EBV is one of the most common viruses to affect humans (it belongs to the family of herpes viruses), and most of us are exposed to it at some point in our lives. EBV is harmless to the majority of people – around 90% of adults have antibodies in their blood indicating a current or past EBV infection – but studies by the Harvard School of Public Health now suggest it could trigger MS in some. After studying blood samples, researchers found the levels of antibodies (immune proteins that show exposure to an infectious agent) to EBV were elevated before the onset of MS. Moreover the researchers noted MS is extremely rare in people who have never had an EBV infection. They also found people who had a specific variant of an immune-related gene, and high levels of antibodies to EBV were nine times more likely to develop MS than those without the gene and with low levels of the antibodies.

Retroviruses and MS

This is pretty exciting stuff. After all, if EBV does trigger MS, we could put our efforts toward finding a way to prevent the disease altogether. But, as with many things in life, it may not be that simple. EBV isn’t the only virus under the MS microscope right now, as some experts are beginning to think human endogenous retroviruses (quite a mouthful – let’s call them HERVs!) may also be involved. Essentially around 5% of the human genome is made up of these ‘fossil viruses’ – remnants of retroviruses (viruses that can integrate in the genome of the host) that infected humans millions of years ago and became silent components of our genetic code. There’s growing evidence some HERVs may be linked with certain autoimmune diseases, including MS.

EBV has previously been shown to activate HERVs in lab studies, and now researchers suspect in some way that virus ‘wakes up’ the dormant HERVs in the body and it’s these that trigger the immune system to go into overdrive. This may explain why people with HIV who are treated with anti-retroviral drugs have a greatly reduced risk of getting MS.

If EBV and HERVs do play a role in triggering MS, anti-retroviral drugs may be able to help to reduce risk of MS in people exposed to EBV. The drugs could possibly even prevent progression of the disease in people who already have MS. There has even been one reported case where the MS symptoms of an HIV-positive patient resolved completely after starting antiretroviral therapy – but of course it’s impossible to draw any conclusions from a single isolated case.

It’s an exciting possibility, but more research is needed. We don’t know, for example, if HIV is capable of suppressing MS, or whether the anti-retroviral drugs could have an impact. A study of patients with relapsing–remitting MS is already underway to investigate whether antiretroviral drugs could really prevent disease progression. It’ll be some time before the results are clear, but one thing’s for sure – researchers are all over it.

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