September 25, 2026, 4:08 pm | Read time: 4 minutes
Almost everyone carries the Epstein-Barr virus (EBV). Usually, it remains unnoticed in the body after an infection for life. New research suggests that the virus could become active again in people with multiple sclerosis (MS) just before a flare-up, triggering processes that promote inflammation. Researchers report this in a recent study in the journal “Nature Medicine.”1
New Evidence of the Link Between Epstein-Barr Virus and MS
The connection between EBV and multiple sclerosis is now considered very likely. Earlier studies showed that an infection with the virus significantly increases the risk of MS.2 However, why the virus contributes to the disease in only a small portion of those affected has been unclear until now.
The current study now provides a possible explanation: In people with relapsing MS, researchers found evidence that the Epstein-Barr virus becomes active again up to three months before a relapse. At the same time, changes were observed in immune cells that are associated with known genetic risk factors for MS.
What is Multiple Sclerosis?
Multiple sclerosis is a chronic inflammatory autoimmune disease of the central nervous system. The immune system mistakenly attacks the protective myelin sheath of nerve fibers, leading to inflammation and disruptions in signal transmission between the brain and body.
Especially at the beginning, the disease often progresses in episodes. Typical symptoms include:
- Vision problems
- severe fatigue (Fatigue)
- balance issues
- numbness
- muscle weakness
The symptoms can appear anew or temporarily worsen.
The Virus Lies Dormant in the Body for Life
The Epstein-Barr virus is part of the herpes virus family. It is primarily transmitted through saliva and is the most common cause of infectious mononucleosis, also known as glandular fever.
After an infection, EBV does not completely disappear from the body. Instead, the virus remains in certain immune cells, primarily in so-called B cells, where it usually stays in a kind of dormant state. Under certain conditions, such as stress or changes in the immune system, it can become active again.
Blood Samples from MS Patients Examined
For the study, researchers analyzed a total of 240 blood samples from 114 people with multiple sclerosis and 21 healthy controls. The participants were from the long-term CLIMB cohort at Brigham and Women’s Hospital in Boston. The unique aspect: Since the samples were collected over years, blood samples from different disease phases were available from the MS patients–including samples taken up to 90 days before a relapse. This allowed scientists to track changes in the immune system over time. Using modern molecular biology methods, they analyzed hundreds of thousands of immune cells and looked for patterns preceding a relapse.
Virus Reactivation Before MS Relapse
The most noticeable changes were seen in B cells–the immune cells where the Epstein-Barr virus prefers to hide. Weeks to months before a relapse, these cells showed signs of virus reactivation. At the same time, risk genes known to increase the risk of MS were activated. The viral signals also triggered a response from other immune cells (such as monocytes), setting off an inflammatory chain reaction in the blood.
Does This Mean EBV Triggers MS Relapses?
Not necessarily. The study only shows a temporal connection. Since it is an observational study, it does not prove that the virus reactivation is the direct cause. Moreover, the virus usually does not fully replicate but rather sends out early warning signals. In people with a genetic predisposition, these signals might be enough to ‘wake up’ the immune system and promote a relapse.
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Could Future Blood Tests Predict Relapses?
The researchers see this as one of the most exciting potential applications of their findings. If the observations are confirmed in larger studies, certain markers for EBV reactivation could help identify patients at increased risk of relapse early on.
So far, disease relapses often become visible only when inflammation is already present in the nervous system. A blood test could provide clues much earlier. However, this is still a future prospect and needs to be verified in further studies.
New Approaches for Therapies
The findings could also be relevant therapeutically. Current MS medications usually suppress larger parts of the immune system. The study authors hope that more targeted treatments can be developed in the future, directly targeting EBV or the involved immune cells. However, whether new medications will actually emerge from this is still uncertain. Years of further research will likely be needed before any practical application.