Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system in which nervous tissue is damaged in several ways. It is often carried out in stages, with periods of exacerbation and remission. It usually occurs among young adults, with a peak incidence between the ages of 20 and 40 (women are more likely to have the disease).
For decades, scientists have been pondering the link between viral infection and multiple sclerosis. New research findings suggest that severe viral infections in adolescence may contribute to disease development in susceptible individuals. This is because the viral infection leads to an overreaction of the immune system that starts the process of demyelination (damaging the sheath) of nerve cells. The process is slow, and the effects in the form of MS become apparent years later. This is confirmed by studies by two independent teams. Researchers analyzed the health records of several million people born in Sweden between 1970 and 1994.
The first investigation into the relationship between viral infection reported in hospital before age 20 and diagnosis of MS after age 20. It was found that infection before age 11 was not associated with any subsequent diagnosis of MS, but incidence of the disease between age 11 and 19 is. Increased risk of multiple sclerosis. Those most at risk were those who had had mononucleosis, pneumonia, or infections of the central nervous system in their teens.
In the second study, researchers focused on the link between MS and infectious mononucleosis, also known as glandular fever, which is caused by the Epstein-Barr virus (EBV). The researchers wanted to know if the viral infection started in MS, or if it was more severe in people at high risk of developing MS due to an abnormal immune system.
“ To confirm that infection is a real risk factor for MS, our latest study compared siblings from the same family. They share many genetic characteristics and lead a similar family life. If one sibling had glandular fever and developed multiple sclerosis, while the other did not develop glandular fever and did not develop multiple sclerosis, this may indicate that glandular fever rather than any genetic predisposition led to multiple sclerosis. On the other hand, Scott Montgomery, the study’s lead author, said that if one of them had glandular fever but both later developed multiple sclerosis, that suggests a genetic predisposition.
The results suggest that viral infection plays an important role in triggering MS, independent of genetic factors. People who had a viral infection between the ages of 11 and 15 were more likely to develop multiple sclerosis later.
Although glandular fever can trigger MS — often in adolescence — it can take many years to diagnose MS. Many people with a viral infection between the ages of 11 and 15 will not be diagnosed with MS until the age of 30. This is because the brain damage caused by MS develops slowly, Montgomery added.
If a severe viral infection may increase the risk of developing neurological diseases later in life, is there a wave of future diagnoses for MS? Could the COVID-19 pandemic contribute to this?
Scientists from the Florey Institute of Neuroscience and Mental Health warned some time ago that the COVID-19 epidemic could be followed by a “silent wave” of Parkinson’s disease. This is because Parkinson’s disease is caused by a number of different factors – genetic and environmental – and SARS-CoV-2’s ability to penetrate the brain can make symptoms worse.
There is no conclusive evidence to suggest that SARS-CoV-2 can cause Parkinson’s disease, but severe infection is undoubtedly a risk factor. COVID-19 may be a specific cause of illness in people who are already susceptible to it. The same may be true in the case of multiple sclerosis.
Only a small number of people with a relatively serious infection in adolescence will later develop multiple sclerosis – in most cases, well under 1%. Montgomery added that other factors, including genetics, are also necessary for disease progression.
“It is possible that the immune response after infection with SARS-CoV-2 contributes to brain inflammation in people genetically susceptible, accelerating the development of MS or even stimulating its progression,” the researchers warn. This means that more waves of disease could emerge in the next 20 years.
However, it must be remembered that the relationship between viral infection in adolescence and multiple sclerosis is still unclear.
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