A strain of herpes virus called HHV-6 plays a role in the development of multiple sclerosis (MS). Investigators at the National Institute of Neurological Disorders and Stroke in Bethesda, Maryland, write that a viral etiology for MS has long been suspected, and that "...recently, human herpesvirus 6, a newly described beta-herpes virus... has been reported to be present in active MS plaques."

The virus infects most people in the first few years of life, and is known to be present in 90% of adult Americans. If the HHV-6 virus is really behind MS, then we also need to know why infection with such a common virus causes diseases in so few people. A study of 36 patients with MS found that 35% of them had detectable levels of active HHV-6 in their serum. Of the patients with the most common form of the disease, the relapsing-remitting form, 70% had an increased immune response to the virus.

The authors list four characteristics of HHV-6 that make it a plausible etiologic candidate for MS. First, primary infection with the virus tends to occur in the first two years of life, causing roseola. In addition, the herpes viruses are known to infect nerve cells, and HHV-6 proteins have been shown to be expressed in MS lesions. Herpes viruses also tend to reactivate, meaning that the virus can lie dormant in nerve cells and cause disease again at a later date. The researchers note that the same factors associated with MS exacerbations have been linked to herpes virus reactivation.

Up to 350,000 Americans have MS, which most often strikes those between the ages of 20 to 40, and is more common in women than in men. Symptoms of the disease include blurred vision, muscle weakness, loss of sensation, and problems with balance.

Nature Medicine (1997;3:1394-1397)