Scientists uncover how common Epstein-Barr virus triggers multiple sclerosis

Researchers have identified how the Epstein-Barr virus (EBV) — present in about 90% of the global population — triggers multiple sclerosis (MS), a finding that also helps explain why existing immunotherapies can slow the disease, Nature reported on 15 July 2026 (https://www.nature.com/articles/d41586-026-02204-1). The results were published in *Science Translational Medicine*.

The study, co-authored by Natalia Drosu, a neurology researcher at Massachusetts General Hospital in Boston, found that immune T-cell activity was twice as high in people with MS as in healthy controls, and that a subtype called CD4+ T cells drives the response to the virus. MS affects around 2.9 million people worldwide, according to the article.

The team measured CD4+ T-cell levels in 60 people with MS before and six months after starting an anti-CD20 treatment, finding the cells had decreased about 2.5-fold; the reduction persisted for up to a year and was validated in a second group. Patients on the therapy also had lower levels of EBV in their saliva than healthy people or those with untreated MS.

The findings help explain how anti-CD20 drugs work: by destroying EBV-infected B cells, they leave CD4+ T cells with less stimulus to attack, reducing nerve damage. Emily Edwards, a rare-diseases researcher at Monash University in Melbourne, said the work shows scientists are "starting to get to the bottom of how Epstein-Barr virus drives the development of multiple sclerosis." There is no cure for MS, but the discovery points to ways to moderate disease severity.

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