A common virus present in nearly 90 percent of Americans may play a role in triggering a multiple sclerosis (MS) relapse, a new study found.
Researchers have found a link between the Epstein-Barr virus (EBV) and MS, positing that active EBV particles may increase in the bloodstream before an MS flare-up.
EBV is a common virus from the herpes family best known for causing infectious mononucleosis, often called ‘mono’ or the ‘kissing disease.’ Once someone catches it, the virus stays in the body for life, usually remaining dormant, but it can sometimes reactivate, often due to stress or a weakened immune system.
It is estimated that 300 million Americans have been exposed to or infected by EBV in their adulthood.
And previous studies have shown that EBV could more than triple the risk of developing MS.
MS affects about one million Americans. The disease occurs when the immune system mistakenly attacks the protective covering of nerves in the brain and spinal cord, scrambling signals between the brain and the body.
In the new study, researchers analyzed both MS patients and healthy control participants using blood samples.
They found there was increased EBV activity in the immune cells of MS patients up to three months before they experienced MS relapse symptoms, such as muscle weakness, vision loss, numbness and severe fatigue.
Researchers found a link between the Epstein-Barr virus (EBV) and MS, showing that EBV activity may increase in the bloodstream before an MS flare up (stock image)
In people experiencing an MS relapse, researchers found that immune cells, particularly B cells, mutated and became more powerful before the flare-up than during it.
The study, published in Nature Medicine, drew blood samples from 114 MS patients and 21 healthy subjects.
They then used molecular techniques, such as single-cell RNA sequencing, to identify which immune system cells changed the most before a flare up.
Single-cell RNA sequencing is when researchers analyze thousands of individual blood cells one-by-one, instead of looking at the sample as one whole mixture.
Researchers discovered that B cells, white blood cells that can harbor inactive EBV, showed the strongest changes.
They saw evidence that the cells were transitioning from their normal state to an activated state, suggesting that something in the body was triggering an immune response. This activation increased before an MS relapse.
Before a relapse, EBV-related signals were associated with turning on genes that are known to increase a person’s susceptibility to MS. This pattern wasn’t seen in the same way when people were in remission or in healthy people.
The study doesn’t provide evidence on how to prevent an MS relapse, but opens doors for new treatment methods that target EBV to help with debilitating symptoms.
‘These findings open a new avenue for targeted therapeutics,’ senior author Dr Tanuja Chitnis said in a press release.
The vast majority of MS sufferers are white women in northern Europe, Canada and the northern half of the US. The autoimmune disorder affects roughly one million Americans
‘Currently, most MS treatments work by broadly suppressing the immune system. Our results suggest there’s an opportunity to be more precise and develop approaches that target EBV or the immune cells involved in relapse,’ Chitnis added.
The exact cause of MS remains unknown, but scientists believe a combination of genetics, environmental triggers, and viral infections — especially EBV — plays a key role.
Mono is extremely widespread, especially in teens and young adults, with about 500 out of every 100,000 people in the US getting it each year.
Although roughly 90 to 95 percent of people carry EBV, only about one in four who are exposed actually develop symptoms of mono.
EBV is primarily spread through saliva. In teens who are first exposed and develop mono, transmission typically occurs via kissing, earning the infection the nickname ‘the kissing disease.’
Mono typically causes extreme fatigue, a severe sore throat, fever and swollen lymph nodes in the neck and armpits.
Many people also develop swollen tonsils with white patches, headaches, body aches and an enlarged spleen, which can rupture if the person engages in contact sports or heavy lifting too soon.
While symptoms usually peak within two to four weeks, the fatigue can linger for months, especially in teenagers and young adults, who tend to experience more severe symptoms than younger children.
In an April 2026 study, published in Neurology Open Access, researchers tracked nearly 19,000 people and found that children and young adults who had lab-confirmed EBV followed by symptomatic mono were significantly more likely to develop MS later in life compared to those who never had EBV-positive mono.
Experts say the findings, published from a population-based study using medical records from the Mayo Clinic-led Rochester Epidemiology Project, underscore the urgent need for preventive strategies, including a potential EBV vaccine, to reduce the long-term toll of the devastating neurological disease.
