No, we’re not talking about the latest cat video.
Most people can faintly recall the horror of having chicken pox as a kid. In fact, being told not to scratch while your mum dabs calamine lotion onto your itchy, blotchy skin is practically a rite of passage. For an unlucky few, varicella zoster (the virus that’s to blame for those itch-inducing spots) can rear its ugly head again in adulthood, returning as herpes zoster. Having lain dormant in the nerve fibres all those years, the virus somehow reactivates, giving rise to painful blisters – a condition known as shingles.
That’s the thing about viruses; particularly ones that belong to the herpes family. Once you’ve been infected, they continue to lurk in the body, ready to strike again. Anyone who suffers from cold sores, another form of herpes virus, will be familiar with this irksome phenomenon.
What’s the Connection with MS?
Unfortunately, scabby lips aren’t the only nasty surprise we have to worry about. There’s mounting evidence that some viral stowaways can increase your risk of other diseases, too – including MS. The Epstein Barr virus (EBV), for example, is another stubborn herpes virus that appears to be a possible trigger for MS: one study in America found people who had a specific immune-related gene and high levels of antibodies to the virus were nine times more likely to develop MS than people without the gene who had low levels of the antibodies.
But it now looks as though EBV isn’t the only strain of herpes that could set off MS – the seemingly harmless herpes zoster virus could, too. After following more than 300,000 adults with shingles and nearly a million people without, researchers in Taiwan have discovered that the infection increases the risk of developing MS in the following year by nearly four times.
OK, most people’s chances of developing MS are very low, so increasing these four-fold isn’t actually a huge difference… That said, the incidence of the disease is much lower in Asia than the West so, in theory, the findings could be more significant if the study is repeated in Europe. But the fact that herpes zoster increases risk at all is what’s interesting.
So what is it about shingles that makes you more likely to get MS? Could the herpes zoster virus trigger the immune system to turn on itself? Well, it’s not quite that simple, of course. We know that around one in four people get shingles in their lifetime, but only a small fraction develop MS, so there’s clearly another factor at play. The researchers who led the study have suggested that rather than causing MS, herpes zoster somehow disrupts the immune system, making the body more susceptible to the disease.
Which kind of tallies with the rest of the evidence we have so far. Several studies point to viral triggers of MS in people who are genetically predisposed, so this latest one definitely adds weight to the theory. Now the researchers will want to take a closer look at what’s going on and rule out confounding factors. The study included no information about whether the people who developed MS smoked or drank, for example).
In the meantime, the more we understand about the role viruses play in MS the closer we get to wiping out the disease altogether. And that goes for pesky chicken pox too!