A common virus may increase the risk of developing multiple sclerosis, new research suggests, bolstering evidence linking the nerve disorder with the Epstein-Barr germ.

CHICAGO, Illinois (AP) — A common virus may increase the risk of developing multiple sclerosis, new research suggests, bolstering evidence linking the nerve disorder with the Epstein-Barr germ.

Harvard University researchers found that women whose blood contained significant levels of antibodies to the Epstein-Barr virus were four times more likely to develop multiple sclerosis than women without high levels.

The virus, a member of the herpes family, is best known as a cause of mononucleosis — the so-called “kissing disease.” It also has been linked to other ailments, including some other nerve disorders and cancers, and is so common that by some estimates it has infected as many as 95 percent of U.S. adults by age 40.

Most exposure to the virus probably occurs in childhood, when there may be no symptoms, but antibodies to the germ would remain into adulthood, said Dr. Alberto Ascherio of Harvard’s School of Public Health.

Coupled with previous research showing that people without Epstein-Barr antibodies rarely develop multiple sclerosis, the findings are “strong evidence in favor of a link,” said Ascherio, lead author of the study in Wednesday’s Journal of the American Medical Association.

However, Dr. Donald Gilden, author of a JAMA editorial and a University of Colorado neurologist, said that while MS probably is caused by a virus, Epstein-Barr probably isn’t the culprit. He said blood tests such as those used in the study are not useful in determining cause and effect.

Nicholas LaRocca of the National Multiple Sclerosis Society said the study shows “a statistical association but not anything that you could really pin down as being causal or anything that really identifies a mechanism.”

About 350,000 Americans have MS, a nerve disease that causes varying degrees of symptoms including numbness, muscle weakness and sometimes paralysis.

It is thought to be an autoimmune disorder, meaning the body’s own disease-fighting immune system mistakes normal tissue as foreign. In MS, a protective nerve-fiber coating called myelin comes under attack. Previous research has suggested that viruses may trigger the autoimmune response in diseases like MS.

One problem with such studies is that it’s unclear which came first — exposure to the virus or multiple sclerosis. LaRocca said determining when MS begins is difficult because symptoms may appear after the disease process has begun.

Ascherio says he sought to avoid that dilemma by studying women who had blood tests as much as 61/2 years before they developed MS.

The authors examined blood samples taken from 62,439 women who participated in a Harvard-based nurses’ health study beginning in 1989. The women gave blood samples in 1989-90 and 1996-99 and were followed up through 1999.

Among them, 144 had multiple sclerosis, though most were thought to have developed the disease before their blood tests. For each woman with the disease, two women without MS were randomly selected, matched by year of birth.

Of 16 women whose blood was taken before they developed MS, 15 had significantly elevated levels of Epstein-Barr antibodies, Ascherio said.

Results of the study of more than 200,000 nurses, in two groups starting in 1989 and 1976, have led to new findings about exercise, stroke and cancer, among other medical issues.