Dalia Rotstein, MD, MPH, on EBV-Negative Multiple Sclerosis Cases and Rethinking Disease Pathogenesis

Mounting evidence over the past several years has positioned Epstein-Barr virus (EBV) as a key environmental factor in the development of multiple sclerosis (MS), with landmark epidemiologic data suggesting that EBV infection may be necessary for disease onset. However, questions remain regarding whether this relationship is universal across all patients and how findings translate beyond highly selected cohorts.

At the 2026 Americas Committee for Treatment and Research in Multiple Sclerosis (ACTRIMS) Forum, held February 5-9 in San Diego, California, Dalia Rotstein, MD, MPH, presented new population-based data exploring whether MS onset can, in some cases, precede EBV infection. Using province-wide laboratory data from Ontario, Canada, her team aimed to address limitations of prior work and better understand EBV-negative or atypical presentations of MS.

In this conversation with NeurologyLive^®, Rotstein discusses the clinical implications of identifying MS cases without documented EBV exposure, how these findings intersect with evolving diagnostic criteria, and what unanswered questions remain in defining the role of EBV in MS pathogenesis.

NeurologyLive: Can you provide an overview of your presentation and why this was a clinically relevant topic?

Dalia Rotstein, MD, MPH: First of all, we’ve known for decades that EBV and infectious mononucleosis increase the risk of developing MS, but it wasn’t known until 2022 when new evidence emerged to suggest that EBV infection is actually a necessary environmental exposure for MS to develop.

This was a study done by Alberto Ascherio and colleagues from Harvard University. They had a very unique cohort from the US military, with blood samples available from around the time people entered the military. They were able to test those samples for EBV serostatus at recruitment and then look at the last blood sample before MS onset.

They found that everybody, except for one individual, had seroconverted to EBV-positive status before developing MS. They calculated a hazard ratio of greater than 32 for the risk of developing MS with EBV seroconversion compared with persistent EBV-negative status. That’s an extremely high hazard ratio and suggested a causal role for EBV in MS.

What we were interested in was looking for cases of MS onset preceding EBV infection in the general population, because there were some important limitations to that work. The US military cohort is different from the general population. It is predominantly male and White, and it only captures people from around age 18, which is older than the average age of EBV seroconversion.

We looked at this question in Ontario, where we have a population of about 16 million. We were able to obtain province-wide laboratory testing data and identify positive tests for primary EBV infection using heterophile antibody testing. Then we identified individuals who had MS onset before that positive EBV test.

How does your research add to or contrast with previous findings on EBV and MS?

The key theory from the 2022 study is that EBV is a necessary environmental exposure for MS. In our study, we found 74 cases of MS onset preceding EBV infection. That’s still a small number, but it’s larger than what we expected to see.

I think this raises the question of whether EBV is truly necessary in 100% of cases. There are several possible explanations. One is that some individuals may have been misdiagnosed with MS. Another is the possibility of misclassification of EBV, such as false-positive lab tests, although these tests generally have 90% to 100% specificity.

The third possibility, which I think we need to consider, is whether there is etiologic diversity underlying what we clinically define as MS. For example, other infections such as HHV-6 have been suggested as potential triggers, so we need to learn more about these EBV-seronegative cases.

Do your findings have implications for EBV-targeted prevention strategies, such as vaccines?

I think EBV vaccines are a really exciting area of research. There are actually a few different EBV vaccines in development, including one in phase 2 clinical trials, so there is a lot of hope there. That said, an EBV vaccine may not provide sterilizing immunity and might instead reduce the severity of infection. Also, the likelihood of administering it in infancy is probably low based on current logistics and policy considerations.

I think it’s unlikely that an EBV vaccine would completely eradicate MS, but it could reduce the frequency of cases and potentially impact other autoimmune diseases like lupus. At the same time, we need to better understand the baseline frequency of EBV-negative MS so that we can evaluate how that changes if vaccination is implemented.

What additional research is needed to better understand EBV’s role in MS?

Specific to our work, I would like to see more studies focusing on EBV-seronegative cases of MS. I don’t think we should dismiss these cases.

For example, in our study, we didn’t have access to full clinical data such as MRI or CSF results. It would be important to evaluate these features in other cohorts. We could look at whether biomarkers differ in these cases, including central vein sign imaging or oligoclonal bands. It would also be interesting to see whether these patients respond similarly to standard MS disease-modifying therapies.

More broadly, there has been a lot of basic science research exploring mechanisms by which EBV might trigger MS. There is evidence of EBV-infected B cells in the brains of patients with MS and studies suggesting molecular mimicry between EBV and CNS proteins. However, these findings are not universal across all cases, and we still lack a single unifying mechanism.

Could evolving diagnostic criteria influence how we study EBV and MS?

I think that’s a very interesting question. The new diagnostic criteria offer greater specificity, which gives us an opportunity to better characterize these atypical cases. For example, tools like central vein sign and paramagnetic rim lesions could be applied to EBV-seronegative cases, but this hasn’t been explored in detail yet. I think that represents a missed opportunity for future research.

There has also been discussion about whether EBV serology could be used to help rule out MS, and whether it could eventually be incorporated into diagnostic criteria. However, I think our findings suggest that would be premature. We don’t yet have enough evidence, and further work is needed to determine whether EBV-seronegative cases represent true MS or a different disease process altogether.

Transcript edited for clarity. Click here for more ACTRIMS 2026 coverage.