Geographic and Climatic Aspects of Multiple Sclerosis

Abstract

Multiple sclerosis has a remarkable geographic pattern with the highest prevalence and mortality rates in temperate zones of both hemispheres and decreasing rates in subtropics and tropics. This difference is associated with geography rather than with race or national origin. No specific exogenous or genetic basis for the geographic pattern has been identified, but it is speculated that some climatologic condition influences the frequency of the disease. It is unknown whether this effect is a direct one on the patient or an indirect effect on the animal or plant life in his environment. Migratory populations have been especially useful in this research and indicate that the rate among those migrating from a high to a low risk area exceeds that of the population into which they have migrated. In the studies of migrating populations, the average minimal latent period from presumed exposure in their prior home to the onset of symptoms has been estimated to be about 9 to 12 years.