The Epstein-Barr virus (EBV) is a major risk factor for MS and may play a role in the condition. However, most people with EBV never develop MS, so other genetic and environmental factors also matter.

MS is an autoimmune condition in which the body attacks myelin — the protective coating around nerve cells in the central nervous system, including the brain and spinal cord. Researchers believe that EBV may be involved in the development of MS and may also play a role in how the disease progresses.

Researchers don’t fully understand how EBV affects MS severity and progression. However, they have found interesting links between MS progression and severity and antibodies that indicate an EBV infection. Here’s what we currently know about EBV and MS.

What Is the Epstein-Barr Virus?

EBV is an extremely common human herpes virus. It’s best known for causing infectious mononucleosis, also known as mono. More than 90 percent of adults worldwide have been exposed to EBV at some point. Nearly 99 percent of people with MS have had EBV, which is one reason it is considered a major risk factor.

EBV infections are often mild or even symptom-free. But in some people, especially those with weakened immune systems, EBV can cause serious complications. It has also been linked to other autoimmune diseases, conditions like MS, and some types of cancer, such as lymphoma, though researchers don’t fully understand this connection.

EBV can infect the epithelial cells, such as those lining the mouth and throat, but is mostly found in B lymphocytes or B cells, a type of white blood cell in the immune system. These infected cells live longer than normal. This allows the virus to stay in the body in a latent, or dormant, state.

How Does EBV Influence MS?

Over the last 40 years, scientists have explored the connection between EBV infection and MS. EBV is believed to contribute to the development of MS, although other risk factors also matter. It’s likely a combination of genetic risk factors and other environmental risk factors that together lead to the development of MS.

Once MS has developed, EBV remains in the body. Research suggests that both the severity and disease progression of MS may relate to how the immune system reacts to the virus. More research is needed to understand this fully, but here’s what we know right now.

EBV and the Immune System

EBV produces viral proteins that cause an immune response in the body. This immune response causes the body to make antibodies against the proteins. Blood tests for EBV include tests for these antibodies. If these antibodies are found in your blood sample, you're considered seropositive for EBV.

The body produces antibodies to various EBV proteins at different stages of EBV infection. Antibodies against EBV appear first during acute infection. Some of these are still detectable at lower levels throughout a person’s life.

Others aren’t detectable in most people after two to four months. After the acute infection has passed, the body creates other antibodies that are detectable for the rest of a person’s life. Your doctor may look for these to find out if you’ve ever had EBV.

EBV, the Immune System, and MS

Some researchers have found that some EBV proteins closely resemble the proteins that make up the myelin sheath around your nerves, which gets attacked during MS. This may cause the immune system to attack myelin while trying to fight EBV, leading to MS.

Levels of EBV antibodies may also differ among the various types of MS, though this also needs more research before we can fully understand it.

EBV may not only be involved in the development of multiple sclerosis — it may also influence how the disease behaves over time. Researchers believe that EBV reactivating in the body could affect how MS relapses and progresses. But more research is needed to know whether this is true and, if so, how it works.

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