Multiple sclerosis has been linked to a teenage viral infection

This conclusion was reached by researchers from several research centers in Sweden and University College London (UK), whose article was published in the journal JAMA Network Open.
Infectious mononucleosis is an acute viral disease caused by the Epstein-Barr virus, which is most commonly contracted during childhood, adolescence and young adulthood. In turn, multiple sclerosis (MS, an autoimmune disease that affects the myelin sheath of the nerve fibers of the brain and spinal cord) is most commonly diagnosed between the ages of 20 and 50. The causes of this disease are still not clear. In particular, it is believed that an increased risk of MS is associated with genetic predisposition, but what are the triggers that trigger the development of the pathology is still unknown.
Previous research by Professor Scott Montgomery and colleagues showed that the risk of MS is significantly increased if a person in adolescence (from 11 to 19 years) was hospitalized with a severe infection, especially one that affects the central nervous system. In particular, we are talking about mononucleosis.
In a new study designed to determine more precisely the role of mononucleosis in the development of MS, scientists analyzed data on nearly two and a half million Swedes born between 1958 and 1994, some of whom were siblings. Nearly six thousand participants over the age of 20 were diagnosed with multiple sclerosis. The researchers proceeded on the assumption that if one of the children in the family had mononucleosis and subsequently got MS and the others did not, it suggests that it was the infection, not a genetic predisposition, that led to multiple sclerosis.   
Analysis of the data showed that mononucleosis between the ages of 11 and 19 years, and especially between 11 and 15 years, when there are very powerful changes in the nervous and immune system, significantly increases the risk of developing MS in the future. As Professor Montgomery explained in his article in The Conversation, the process of damage to the myelin sheaths of nerve fibers is very slow and unnoticeable at first, so the diagnosis of multiple sclerosis is usually made only closer to the age of 30.