The Epstein-Barr virus (EBV) is our constant companion, infecting an estimated 90%-95% of adults. Many of us are first infected as children, when the germ may trigger cold and flu symptoms. EBV also causes mononucleosis, or kissing disease, a glandular fever that has afflicted generations of amorous young people.
Post infection, EBV settles in for the long haul and remains in the body until death. It's thought to be largely innocuous, but EBV is now implicated as a cause of several types of cancer — including lymphoma and nasopharyngeal tumors — and multiple sclerosis (MS). In 2022, a landmark study in Science suggested that previous EBV infection is the primary cause of MS.
While there aren't many implications for current treatment, greater insight into the origin story of MS may eventually help neurologists better diagnose and treat patients, experts said. The goal is to uncover clues that "can help us understand MS a little bit better and reveal insights that could lead to new disease-modifying therapy," Bruce Bebo, PhD, executive vice president of research with the National MS Society, told Medscape Medical News in an interview.
EBV Boosts MS Risk 32-Fold
EBV was first linked to MS back in 1981. For the 2022 study, researchers at the Harvard T.H. Chan School of Public Health and Harvard Medical School analyzed blood serum from 10 million active-duty members of the US military. They focused on 801 recruits with MS and matched them with more than 1500 controls. All but one of those with MS had been infected with EBV; infection appeared to boost the risk for MS 32-fold (95% CI, 4.3-245.3; P < .001).
Neurologist and associate professor Michael Levy, MD, PhD, of Harvard Medical School and Massachusetts General Hospital, said in an interview that the findings are "groundbreaking" and confirm that EBV is "likely the primary cause of MS."
According to Levy, there are two main theories about why EBV causes MS. The first hypothesis, known as the "molecular mimicry" theory, suggests that "EBV is a trigger of MS, possibly when the immune system mistakes a viral protein for a myelin protein and then attacks myelin," Levy said. In MS, the immune system attacks the protective myelin sheath and the axons it insulates.
"After that point, the virus is not necessary to maintain the disease state and eradicating the virus likely won't have much effect since the immune response is already triggered," he said.
The second theory is that "EBV is a driver of MS where there is an ongoing, lifelong immunological response to EBV that continuously causes damage in the central nervous system [CNS]. In theory, if we could eradicate the virus, the destructive immune response could also resolve. Thus, an EBV antiviral treatment could potentially treat and maybe cure MS," Levy explained, noting that "removing the pathogenic antigen may be a more effective strategy than removing the immune response."
However, "we don't yet know which hypothesis is correct," he said. But "there is preliminary evidence in favor of each one."
'Additional Fuses Must Be Ignited'
It's also unclear why most people infected with EBV do not develop MS. It appears that "additional fuses must be ignited," for MS to take hold, according to a commentary accompanying the landmark 2022 study.
"As far as clinical implications, knowing whether a patient has a medical or family history of mononucleosis may be a small clue, a small piece of evidence, to help with diagnosis," Bebo said.
He agreed with Levy that an antiviral could be a promising approach "If the problem in MS is a dysfunctional immune response to EBV."
Natalia Drosu, MD, PhD, a postdoctoral fellow at Harvard-MIT Biomedical Engineering Center, told Medscape Medical News that a clinical trial of a non-immunosuppressive antiviral targeting EBV in patients with MS would be a crucial step toward better understanding the MS-EBV connection. "If we learn that antivirals are effective in MS, we should develop non-immunosuppressive therapies for patients with MS as soon as possible," she said.
Stanford University's Lawrence Steinman, MD, a professor of Neurology and Neurological Sciences, Pediatrics, and Genetics who coauthored the commentary on the original Science paper, agreed that it's worth investigating whether antiviral therapies targeting EBV will benefit patients who already have MS. But he cautioned against clinicians experimenting on their own outside of a research study. "You'd want to use the right antiviral and a properly designed trial," he told Medscape Medical News.
Antivirals May Place a Crucial Role in MS Control
While there are no approved therapies for EBV, several MS disease-modifying therapies have anti-EBV effects, Levy said, citing anti-CD20 therapy as a clear example. It depletes B cells from the circulation, and it depletes EBV because the virus lives in the B-cell compartment. "Some MS treatments may be inadvertent EBV antivirals," he said.
Researchers are also thinking about how they might exploit the MS-EBV link to prevent MS from developing in the first place, but there are uncertainties on that front too.
Conceivably, there may be some way to intervene in patients to treat EBV and prevent MS, such as a unique treatment for infectious mononucleosis (IM), Levy said.
Researchers are especially intrigued by signs that the timing of infection may play a role with people infected with EBV via IM after early childhood at especially a high risk of developing MS. A 2022 German study calculated that people who developed IM were almost twice as likely as those who didn't to develop MS within 10 years, although the risks in both groups were very small. Subgroup analysis revealed the strongest association between IM and MS was in the group infected between age 14 and 20 years (hazard ratio, 3.52; 95% CI, 1.00-12.37). They also saw a stronger association in men than in women.
The authors of a 2023 review in Clinical & Translational Immunology wrote that "further understanding of IM may be critical in solving the mystery of EBV's role [in MS]."
Levy said this line of questioning is important. "In theory, if we can tell who is prone to develop MS or whose immune system might be reacting to EBV to cause MS, we can intervene early to prevent neurological manifestations."
However, "remember that while most of the world gets EBV infections, only 1 in 1000 will get MS. So, it might not be feasible to test everyone before neurological manifestations occur," he said.
More Questions to Answer About EBV and MS
Researchers hope to answer several questions moving forward. For one, why is EBV uniquely connected to MS? "You would think that if there were cross-reactivity to myelin, there are many viruses that could cause MS. But the association seems to be very restricted to EBV," Levy said. "It is probably due to the fact that EBV is one of the only human viruses that can infect B cells, which play important roles in controlling immune responses."
The molecular mimicry theory also opens up a potential treatment pathway.
A 2022 study by Steinman and colleagues reported "high-affinity molecular mimicry between the EBV transcription factor EBV nuclear antigen 1 (EBNA1) and the central nervous system protein glial cell adhesion molecule (GlialCAM)." Antibodies against EBNA1 and GlialCAM are prevalent in patients with MS. In a mouse model of MS, the researchers showed that EBNA1 immunization exacerbates disease. The authors wrote that "Our results provide a mechanistic link for the association between MS and EBV and could guide the development of new MS therapies."
Could an EBV Vaccine Be the Answer?
On the prevention front, perhaps the most obvious question is whether an EBV vaccine could eliminate MS for good?
Bebo, from the National MS Society, said it will be important to determine which kind of vaccine is best. Is it one that neutralizes infection with EBV? Or is it enough to simply prevent clinical manifestations?
Both types of vaccines are in development, and at least two clinical trials are now in the works. The National Institute of Allergy and Infectious Diseases is sponsoring a phase 1 study of an adjuvanted EBV gp350-Ferritin nanoparticle vaccine. A total of 40 subjects aged 18-29 years will take part: 20 with EBV and 20 who are not infected. The study is expected to end in 2025.
There is also a phase 1 placebo-controlled study in progress testing an EBV vaccine based on mRNA-1189 in 422 subjects aged 12-30 years. This trial is also due to end in 2025.
"This is very exciting, but it may take a decade or two to determine whether a vaccine is effective at preventing MS," Levy said.
Levy, Steinman, Drosu, and Bebo had no disclosures.
Randy Dotinga is a freelance science or medical journalist and board member of the Association of Health Care Journalists.