A new study suggests having the disease infectious mononucleosis, often called mono, caused by the Epstein-Barr virus is linked to an increased risk of developing multiple sclerosis. The study’s authors noted it does not prove that mono caused by the Epstein-Barr virus causes MS; it only shows a link. 

The Epstein-Barr virus is a herpes virus that is extremely common but causes no symptoms in most people. However, when a person contracts the virus as a teenager or adult, it can lead to mononucleosis. The Epstein-Barr virus is the most common cause of mono. 

For this study, researchers at the Mayo Clinic in Rochester, Minnesota, examined more than two decades of healthcare records to find people who had a positive test for Epstein-Barr virus infection and a diagnosis of infectious mononucleosis. The 4,721 people the researchers identified were then each compared to three people of the same age and sex who had or not had mono, or 14,163 people. 

The people who had mono were followed for an average of six years. The people without mono were followed for an average of eight years. During that time, eight people with a history of mono developed MS, or .17 percent. This represented 2.25 cases per 10,000 person-years. Person-years represent both the number of people in the study and the amount of time each person spent in the study. For the group without mono, 10 people developed MS, or .07 percent. This represented .77 cases per 10,000 person-years. 

Researchers then adjusted for other factors that could affect the risk of MS, such as race and ethnicity, smoking status and whether participants had other conditions such as diabetes, depression, and substance use disorders. After adjustment, they found that people with a history of mono were three times more likely to develop MS than people without mono.

A limitation of the study is that participants were followed for an average of six to eight years, so it’s possible that MS could develop later in life for some people. 

The study was published in the journal Neurology Open Access.