A virus believed to infect up to 95 percent of all Americans may play a crucial role in triggering multiple sclerosis, Harvard researchers reported yesterday, potentially providing an important clue to understanding a debilitating disease whose root causes have eluded scientists for decades.
Even as treatments have improved for the 400,000 MS patients in the United States, researchers have struggled to unravel the molecular secrets of a disease that has been blamed on everything from genetics to geography.
"It's not easy to find the causes of any disease, but in terms of MS especially, we know very little," said Dr. Alberto Ascherio, the Harvard epidemiologist who directed the MS study.
Researchers from the Harvard School of Public Health, writing in yesterday's Journal of the American Medical Association, provide some of the most persuasive evidence so far that the Epstein-Barr virus may play a role in the cascade of genetic and environmental forces that combine to cause MS, a chronic condition that hobbles the central nervous system.
With that kind of knowledge, scientists might develop more effective methods for treating MS or even vaccines.
Until recently, doctors found it challenging to make a definitive diagnosis of MS, with symptoms varying drastically from patient to patient. In some, the disease manifested itself in blurred vision or loss of balance. In others, the symptoms might include tremors, numbness and impaired speech.
Advances in technology, such as magnetic resonance imaging, have aided substantially in identifying cases of MS, but doctors and patients continue to puzzle over what causes the disease.
"I'm frustrated that there's not more knowledge, frustrated that there's not a cure yet," said Krista Milne, a 37-year-old Newton mother with MS who is involved in the Boston Cure Project for Multiple Sclerosis.
Investigators had long speculated that viruses or bacteria might somehow trigger MS, with some researchers focusing on various herpes viruses. Among those suspected: Epstein-Barr, which is transmitted through saliva and often infects infants and toddlers.
In youngsters, the virus typically results in few health problems. But in teen-agers and young adults first exposed to the virus, severe mononucleosis can result.
The Harvard researchers wanted to know whether there was a way to demonstrate an association between Epstein-Barr and multiple sclerosis.
They reviewed blood samples routinely drawn from U.S. military personnel, identified 83 men and women with definite or probable cases of MS, and compared them with military personnel not diagnosed with the disease.
They found that the MS patients had much higher levels of Epstein-Barr antibodies, immune-system cells that target the virus.
In fact, some of the patients had 20 times as many of those immune cells as people without MS. The researchers also discovered that those markers of elevated immune-system response were evident in the patients' blood years before they were diagnosed with MS.
They can't say for sure why some patients' immune systems churn out a stronger response to Epstein-Barr, although researchers have suggested that people infected with the virus later in life have a more robust immune response.
Harvard researchers and MS specialists said the findings do not establish a definite link between the virus and MS; rather, the data provide another valuable path of investigation.
"This is absolutely on the right track," said Dr. Tim Vartanian, an MS specialist at Beth Israel Deaconess Medical Center. "The most important thing to do is to take a step back and identify root causes of this disease, but trying to identify root causes is one of the areas that is understudied and underfunded."