Within Europe, Scandinavia, The British Isles, the Low Countries and Germany have very high rates. Canada, northern USA and New Zealand have an equivalently high prevalence. Why MS is distributed around the world the way it is is not well understood. There are two main features of the prevalence data for MS that need to be explained. Unfortunately, no convincing explanations are available, though this is not for the lack of attempts.
Many theories abound.
Many pathogens have been examined to this end, including Epstein-Barr virus and various other retroviruses, though as with all pathogen work with MS, it has produced many dead ends. Some suggest that MS is common in temperate regions due to the seasonal fluctuations in daylight affecting body chemistry. Levels of neurotonin and other biochemicals have been shown to vary with the seasons but why these would affect MS susceptibility is unclear. Still others suggest that the differences in concentrations of minerals in temperate soils versus tropical ones affect the human intake of these chemicals through the plants we eat and the water that we drink. It is suggested that these variations make people more susceptible to the disease.