Study examines blood samples of over 10 million young adults to find links

Epstein-Barr virus (EBV) infection may be a trigger event that leads to multiple sclerosis (MS), an observational study found.

Among more than 10 million young adults on active duty in the U.S. military, risk of MS increased 32-fold after infection with EBV but was unchanged after infection with other viruses, including the similarly transmitted cytomegalovirus (CMV), according to Alberto Ascherio, MD, DrPH, of Harvard T.H. Chan School of Public Health in Boston, and co-authors.

Serum levels of neurofilament light chain (NfL), a non-specific marker of axonal injury, increased only after EBV seroconversion, the researchers reported.

“These findings cannot be explained by any known risk factor for MS and suggest EBV as the leading cause of MS,” they wrote in Science.

“The hypothesis that EBV causes MS has been investigated by our group and others for several years, but this is the first study providing compelling evidence of causality,” Ascherio said in a press release. “This is a big step because it suggests that most MS cases could be prevented by stopping EBV infection, and that targeting EBV could lead to the discovery of a cure for MS.”

“Currently there is no way to effectively prevent or treat EBV infection, but an EBV vaccine or targeting the virus with EBV-specific antiviral drugs could ultimately prevent or cure MS,” Ascherio added.

The findings provide “compelling data” that implicate EBV in the development of MS, observed William Robinson, MD, PhD, and Lawrence Steinman, MD, both of Stanford University, in Palo Alto, California in an accompanying editorial. “Infection with EBV is likely to be necessary, but not sufficient, to trigger development of MS,” they wrote.

“Nearly everyone is infected with EBV, but only a small fraction develop MS,” Robinson and Steinman noted.

“The mechanism (or mechanisms) of EBV-mediated MS development remains elusive,” but possibilities include molecular mimicry, through which EBV viral protein sequences mimic human myelin proteins and other CNS proteins and thereby induce autoimmunity against myelin and CNS antigens,” they added.

EBV has been considered a top candidate for a causal role in MS given increased MS risk after mononucleosis, with evidence for increased serum antibodies to EBV nuclear antigens in MS patients, and EBV in some MS lesions studied pathologically.

“Causality implies that some individuals who developed MS after EBV infection would not have developed MS if they had not been infected with EBV,” Ascherio and co-authors wrote. “Ruling out a randomized trial, the gold standard to study this counterfactual occurrence is an ’experiment of nature,’ a longitudinal investigation of MS incidence in a cohort of EBV-negative individuals, some of whom will be infected with EBV during the followup and some who will not.”

Data and stored blood samples from a database of more than 10 million active duty U.S. military members between 1993 and 2013 provided an opportunity to investigate a causal link, the researchers noted.

All people in the database were initially MS-free, as MS is a disqualifying condition for military service. A total of 955 incident cases were diagnosed during the study period. In 2019, 45.7% of the members were age 25 or younger, 83.1% were male, and 68.8% were White.

Blood samples were obtained and stored at the beginning of military service and every 2 years thereafter. A preliminary study found 5.3% in the database were EBV negative at first sample.

For the present study, evaluations included EBV serology, CMV serology, serum NfL (which is a possible MS biomarker), and VirScan to determine whether reaction to proteins from any known human virus was evident. The analysis included 801 service members diagnosed with MS during active duty and 1,566 matched controls.

The HR for MS with EBV seroconversion versus persistent EBV seronegativity was 32.4 (95% CI 4.3-245.3, P<0.001). Median time from first positive EBV sample to MS onset was 5 years.

Of the 801 MS cases, only one occurred in a patient whose last sample (a median of 1 year before MS onset) was EBV-negative. That person may have contracted EBV after the last blood sample or may have been an example of the “uncommon but nevertheless regular phenomenon” of lack of seroconversion after infections or vaccines, Ascherio and co-authors noted.

Among people who went on to develop MS but were EBV seronegative at baseline, serum NfL levels were similar to non-MS controls until after EBV infection, when they were elevated among those who would develop MS. “Thus, there were no signs of neuroaxonal degeneration before EBV seroconversion in individuals who later developed MS, indicating that EBV infection preceded not only symptom onset but also the time of the first detectable pathological mechanisms underlying MS,” the authors wrote.

CMV seroconversion, which was used to assess predisposition to both infection and MS, occurred at similar rates in people who did or didn’t develop MS. VirScan applied to a sample of 30 people who developed MS and 30 controls found that antibody responses to peptides from all known human viruses were similar in both groups, except for EBV.

This indicates “that the preclinical and early clinical phases in MS are not associated with immune dysregulation affecting general susceptibility to infection,” the authors wrote. It also supports the specificity of the association between EBV and MS and “argues against a second hit from another virus playing a major role in MS etiology,” they added.

“A causal interpretation of our results requires ruling out the possibility that systematic differences between individuals who seroconverted and those who remained EBV-negative explain the results,” Ascherio and co-authors pointed out.

“Confounding by known factors is virtually ruled out by the strength of the association,” they wrote, noting that the 32-fold increase in MS risk seen would require a candidate confounder to confer >60-fold risk of MS. No known or suspected risk factors for MS have such strong associations and the existence of a still unknown factor that increases risk of both EBV infection and MS by >60 fold is “rather implausible,” they suggested.

Reverse causation is unlikely since VirScan results suggested there was no immune dysregulation in the pre-clinical phase of MS increasing general susceptibility to infection, they added.

Considering prior evidence that MS risk remains elevated 15 or more years after infection and that anti-EBV nuclear antigen antibodies strongly predict MS risk 15-20 years after infection, the researchers suggested that “collectively, these findings strongly suggest that the occurrence of EBV infection, detectable by the elicited immune response, is a cause and not a consequence of MS.”

“One of the most successful treatments for MS is anti-CD20 monoclonal antibodies, which deplete circulating memory B cells, the primary site of persistent latent EBV infection,” Ascherio and co-authors noted. “Directly targeting EBV could have major advantages compared with anti-CD20-based therapies, which have to be administered by intravenous infusion and may increase the risk of infections.”

  1. Epstein-Barr virus (EBV) infection may be a trigger event that leads to multiple sclerosis (MS), an observational study found.

  2. Among more than 10 million young adults on active duty in the U.S. military, risk of MS increased 32-fold after infection with EBV but was unchanged after infection with other viruses.

Paul Smyth, MD, Contributing Writer, BreakingMED™

This work was supported by the National Institute of Neurological Disorders and Stroke, National Multiple Sclerosis Society, German Research Foundation, and NIH Directors Early Independence Award.

Ascherio reported no competing interests.

Robinson is a coinventor on a patent application filed by Stanford University that includes antibodies to EBV.

Cat ID: 36

Topic ID: 82,36,730,125,190,36,192,925