Comparative epidemiological studies of multiple sclerosis in South Africa and Japan.

Evidence is presented pointing to an increased incidence of multiple sclerosis having taken place in South Africa during the period 1964 to 1970 and in Tokyo, Japan, during the period 1966 to 1972. There is a possibility that these changes in incidence point to the introduction during the years immediately after the second world war, of an infective element-probably from a high-risk area-to Tokyo and South Africa. If this is so, it lends support to the theory of an infective basis for multiple sclerosis and that the suspected infection in prepubertal susceptibles may produce the symptoms of multiple sclerosis years later. Other factors relevant to multiple sclerosis such as environmental changes, improved diagnostic techniques, and susceptibility are discussed.