Multiple sclerosis in the Faroe Islands: an epitome

The Faroe Islands are a semi-independent unit of the Kingdom of Denmark and are located in the North Atlantic Ocean between Norway and Iceland. Effort s to identify all cases of multiple sclerosis (MS) since 1900 among Faroese have been continuing for over a quarter century. As of 1998 prevalence was 66 per 100,000, age adjusted to 1960 US population, with a rate of 100 for women and 34 for men. Median survival was at 29 to 34 years with no signif icant difference by sex. Faroese with overseas residence indicated that at least 2 years of exposure from age 11 on in a high-risk area are required f or acquisition of MS. Among native resident Faroese the first instance of s ymptom onset was in 1943, heralding a type 1 epidemic of 21 cases. This was followed by three successive epidemics of 10, 10, 13 cases, with membershi p in each epidemic defined by calendar time and age of exposure. Age at exp osure for epidemic I was 11 to 45 years; for later epidemics age 11 was the minimum. We believe the source of MS on the Faroes was their occupation by British troops for 5 years in World War II. We think they introduced a wid espread, specific, persistent (but unknown) infection, probably asymptomati c, which we call the primary multiple sclerosis affection (PMSA). Only a sm all proportion of those affected with PMSA will years later show any clinic al signs of MS. Models of transmission of PMSA through successive cohorts o f Faroese fit the-data for epidemics II and III, and predicted the occurren ce of epidemic IV. The Faroese provide an ideal location to determine the n ature of PMSA, since the disease has remained geographically stable for 50 years without further spread throughout the islands. (C) 2001 Elsevier Scie nce Inc. All rights reserved.