Multiple sclerosis (MS) if most frequently diagnosed in individuals between the ages of 20 and 50. Specific genes put a person at higher risk of contracting the disease, which affects the central nervous system. However, researchers are still seeking to understand the triggers. Some scientists have found evidence that having pneumonia in adolescence is linked to a greater risk of MS. This evidence has led to other research into infections that may be associated with MS.
Studying the connections has some obstacles to overcome. Infections may be a result of MS instead of the opposite. And, it may be 5 to 10 years or more between the initial phases of MS and the first symptoms, which include tingling, numbness, stiffness, vision problems, difficulty with balance, and fatigue. Scientists pursuing these studies need to take extra precautions to be certain that the infections that occurred prior to the MS became evident.
One study published in the journal Brain examined the health records of close to 2.5 million people born in Sweden between 1970 and 1994. Approximately 4,000 of them received an MS diagnosis after the age of 20. Of those 4,000, 19% had an infection diagnosed between birth and 10 years of age, and 14% of them were between 11 and 19 years of age.
The study found that most infections prior to age 11 were not linked to a later diagnosis of MS. However, infections diagnosed in a hospital, which means the infections were severe, between 11 and 19 were linked consistently with an elevated risk of developing MS.
Not every category of infection resulted in a higher risk of MS. However, infections of the central nervous system raised the risk of MS most notably. The researchers noted that inflammation in the central nervous system may induce the autoimmune process, which occurs when an individual’s immune system attacks their own body, which results in MS.
Respiratory infections in adolescence were also linked to a higher risk of developing MS, increasing the risk by 51%. The researchers believed that in some cases, inflammation and infection in the lungs may lead to immune activation in other parts of the body like the central nervous system. The increases the risk of inflammation in those areas. This might help to explain how a lung infection could induce the MS disease process. Or, the infecting agent may have some direct influence on the brain.
Infection with the Epstein-Barr virus (EBV) has been associated with MS for a long time. The researchers needed to ensure that the increased risk they found was not due to an EBV infection. After excluding the people who had previously experienced an EBV infection, known as glandular fever, the results of the study remained the same. This points out the importance of various types of infection during adolescence and the higher risk of MS.
For even more certainty that the infections in adolescence were likely to pre-date the initial asymptomatic development of MS, the researchers repeated their work, bu included only an MS diagnosis after age 25. The higher risk of MS linked to infections in adolescence remained the same for infections in the lungs and central nervous system. There was a minimum of 5 years between infection and MS diagnosis, typically longer, indicating that the disease progresses slowly until there is sufficient damage to the brain for symptoms of multiple sclerosis to develop.
This study provided more evidence that adolescence is a period of heightened susceptibility to exposures linked with a higher risk of MS. In addition, there may be many years between exposure and an MS diagnosis. These results offer insight into the types of exposures that may increase the risk of MS.
Further studies will investigate whether people who are genetically susceptible to developing MS are more likely to have a more pronounced immune reaction to infections increasing the likelihood of hospital admission.
Several but not all types of infections are associated with MS, particularly those that may be able to cause inflammation in the central nervous system. Only a few people who have relatively serious infections in adolescence will go on to have MS (in most instances much lower than 1%), as other factors, including genetic susceptibility, are also needed for the disease to develop.