The prevalence is high in the developed countries like the US, Westeren Europe and Australasia. Other Asian countries comes next. The lowest incidence in in Africa.
Recently (during the last one year) I became aware of four cases in just one town in SL. They are trying all sorts of treatment and drugs including Riluzole. Riluzole is quite expensive, and really isn't a cure, It can only reduce the symptoms and prolong the median survival.
Not so sure about the prevalence in SL, but the estimated total could be around 500 or more cases.
Remember the "Ice Bucket Challenge"? That was done to make awareness of this disease.