Epidemiological studies of MS, in the Faroe Islands, supported an infectious cause of MS. The Faroe Islands had no known reports of MS prior to 1943, among native-born residents. The Faroe Islands were occupied by British troops for five years during World War II, and many of the soldiers were from the Scottish Highlands, an area with a high rate of MS. The troops are believed to have introduced a widespread, specific, persistent (unknown) infection that triggered multiple sclerosis, 2-6 years after exposure.

The Faroe Island studies and others epidemiological studies support that a chronic infection may trigger MS, years after the initial exposure to an immortal infectious pathogen.