Multiple Sclerosis and Microbes

Abstract

Multiple sclerosis [MS] is the second commonest cause of chronic neurological disability after traumatic injuries. There is marked geographical difference in incidence between countries in temperate and tropical or subtropical regions of the world. Although this has been attributed to sun exposure and differences in the prevalence of vitamin D deficiency, this may be related to microbial exposure. The pathogenic mechanism of MS is complex and involves multiple genetic and environmental factors. MS is an immune-related demyelinating disease of the brain and spinal cord, but the inciting agent is unknown. Many naturally occurring demyelinating diseases of the nervous system of animals and humans are of viral origin. The hygiene hypothesis of the burden of microbial exposure in early life has been suggested to be the factor responsible for increased prevalence of immune-related disorders, such as MS and asthma in affluent countries in temperate zones. The strongest evidence in favor of a role of microbes in the pathogenesis of MS is infection with Epstein–Barr virus at a critical age [adolescence and early adulthood] in the genetically predisposed person, which occurs in >60 % of the population in temperate developed countries compared to <10 % of the population in warmer developing countries. This chapter also discusses the evidence implicating other microbes such as human herpes virus-6 and human endogenous retroviruses.