Common virus may play a role in debilitating neurological disorders

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Common virus may play a role in debilitating neurological disorders


For decades, researchers have suspected that people infected with an extraordinarily common virus, Epstein-Barr, are more likely to develop multiple sclerosis, a neurological disease that affects one million people in the United States. Now a team of researchers is reporting what some believe to be the most compelling evidence yet of a strong link between the two diseases.

The virus infects almost everyone in their teens or young adult years, and few develop multiple sclerosis. The researchers also note that it is not the only known risk factor for people developing the disease. But they say their data indicates this is the clearest of all. While it remains to be seen whether the finding will result in treatments or cures for multiple sclerosis, the study may further motivate research into therapies and vaccines for the condition.

In their study, published Thursday in Science, the group examined data from 10 million people on active duty in the United States armed forces over two decades. The strength of their study, said the lead researcher, Dr. Alberto Ascherio, an epidemiologist at the Harvard TH Chan School of Public Health, is that they could track people for years and ask whether Epstein-Barr infections preceded multiple sclerosis.

Among the servicemen in the study, 801 developed multiple sclerosis, a debilitating disease that occurs when the immune system attacks the fatty insulation that protects nerves in the brain and spinal cord. Most who develop the disease are diagnosed between the ages of 20 and 50. However, the disease is rare — a person’s chance of developing multiple sclerosis is half a percent.

At the same time, the virus in question, Epstein-Barr, is very common and infects almost everyone in the population at some point. While few know they were infected, some develop mononucleosis. The virus remains in the body for life.

Because so few people with the virus develop multiple sclerosis, it cannot be the sole cause of the disease. Other risk factors have been identified, including some, such as low levels of vitamin D and smoking, previously seen by the Harvard group using the same data set. There are also genetic factors — 900 abnormal genes have been identified in patients with multiple sclerosis, said Dr. Anthony J. Reder, a multiple sclerosis expert at the University of Chicago, who was not involved in the new study. Gender also plays a role; most patients are women.

But, said Dr. Ascherio, no risk factor stands out like Epstein-Barr infections.

To ask to what extent the virus increases the risk, the researchers studied the small proportion of people who were not infected with the virus early in their career, but became infected afterwards. They discovered infections due to the presence of antibodies against the virus.

Of patients with multiple sclerosis, 32 out of 33 became infected with Epstein-Barr before developing MS

As a control group for their study, the scientists followed 90 individuals who were not initially infected with Epstein-Barr and who also did not develop multiple sclerosis. Of them, only 51 subsequently became infected with Epstein-Barr.

That meant that an Epstein-Barr virus infection increased the risk of multiple sclerosis more than 30-fold, said Dr. Asherio.

But dr. Reder warned that it could be difficult to determine cause and effect from an epidemiological study. People who develop multiple sclerosis have an overactive immune system that causes them to develop high levels of antibodies against viral infections. Multiple sclerosis cannot develop from the virus, but from the body’s response to it.

“Multiple sclerosis patients have fewer viral infections than normal,” he said, because their immune systems are so active that they fight viruses effectively. “Multiple sclerosis patients often say, ‘I never get a cold.’ When I hear that, my ears perk up.”

The drugs currently used to treat multiple sclerosis suppress the immune system, Dr. Red on. So far, he added, antiviral drugs have not helped patients with multiple sclerosis.

The Harvard group tried to check for the possibility that the immune system’s response, not the virus itself, increases the risk of multiple sclerosis in those infected with Epstein-Barr. They asked whether antibodies to another common virus, cytomegalovirus, were also linked to a greater risk of multiple sclerosis. There were not.

But cytomegalovirus, said Dr. Reder, for unknown reasons, appears to protect against multiple sclerosis. So the fact that those infected with it did not have a higher risk of multiple sclerosis may not be surprising.

Others said the study was compelling evidence of cause and effect.

“The way it was done is pretty compelling,” said Dr. Michael David Kornberg, a multiple sclerosis specialist at Johns Hopkins. “It’s really the most conclusive data we’ve had for a causal relationship.”

That leaves the question of what to do next.

dr. Bruce Cree, a multiple sclerosis researcher at the University of California, San Francisco, noted that it can be difficult to treat multiple sclerosis by going after Epstein-Barr because it can be difficult to transmit the actual virus in patients. find. Although multiple sclerosis is a disease of the brain and spinal cord, he could not find the virus in the patient’s spinal fluid.

But patients appear to harbor cells in their brains that produce antibodies to the Epstein-Barr virus. dr. Cree is investigating whether he can treat multiple sclerosis patients by eradicating those cells that are infected with Epstein-Barr.

and dr. Lawrence Steinman, a multiple sclerosis researcher at Stanford who wrote a perspective accompanying the Harvard group paper, said an experimental mRNA vaccine against Epstein-Barr was one of a number of approaches designed to prevent the virus from spreading. affects the brain.

The question now, he said, is, “Can we make multiple sclerosis go away?”

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