A new study has yielded strong evidence linking a strain of herpes virus to multiple sclerosis (MS). More than 70% of patients in the study with the most common form of MS showed levels of active herpes virus-6 (HHV-6) in their blood serum. The finding is reported in the December issue of Nature Medicine.
In multiple sclerosis, immune cells attack and inflame myelin, the fatlike sheaths of neurons in the central nervous system. HHV-6 also inflames myelin, according to work done by virologist Steven Jacobson and his colleagues at the National Institute of Neurological Disorders and Stroke in Bethesda, Maryland. The virus infects, nearly exclusively, young children, leading to a condition called roseola, which is marked by high fever and rashes.
The researchers looked for signatures of HHV-6 in the serum of 36 MS patients and 66 controls in a blind test. As expected, nearly all showed IgG, the long-term antibody response to HHV-6 antigens. But 73% of MS patients also had IgM, an early antibody response to HHV-6 antigens and a potential marker of active virus replication. Only 18% of the control group showed IgM. Just as revealing, DNA from the virus was found in more than one-third of MS patients, but in none of the controls. Moreover, magnetic resonance imaging detected numerous lesions in the myelin in the brain of a recently deceased MS patient, and an autopsy revealed HHV-6 in the lesions, but not in the adjoining normal tissues.
The new findings won't lead directly to a cure, Jacobson cautions, because nothing is yet available that can kill the virus without aggravating demyelination. Other experts suggest that HHV-6 could be a symptom rather than a cause of MS. "MS breaks down the blood-brain barrier," says Patricia O'Looney, a biochemist with the National Multiple Sclerosis Society in New York City. "Destruction of the tissues may allow the virus to migrate into the central nervous system," where it simply appears to be the culprit.