The question at Quora was:

Did the Cameron Highlanders bring a cold virus to the Faroe Islands in WW2 that damaged the immune system and the testicles and ovaries of the Faroe islanders and make them vulnerable to multiple sclerosis?

My answer was:

A leading hypothesis for the cause of multiple sclerosis is that it’s an autoimmune disease that starts with a genetic predisposition, that’s triggered by a viral infection.  It may be a specific virus, but it’s more likely that it can be triggered by any of a wide range of viruses, which may be innocuous on their own and require other genetic and environmental factors to cause MS.

The timing of MS on the Faroe Islands shows a dramatic increase starting in 1943, and waxing and waning over multi-year periods, consistent with a role for an infectious agent:
Multiple sclerosis: variation of incidence of onset over time in the Faroe Islands.

It’s been suggested that British troops spread a very mild virus among the inhabitants that led to the disease among the inhabitants:
Epidemiology in multiple sclerosis: a pilgrim’s progress.

The hypothesis is controversial, and other researchers raise evidence opposing it and supporting a genetic role:
Multiple sclerosis in a family on the Faroe Islands.

However, neither hypothesis seems to fully account for the possibility that both genetics and infectious diseases could be critical factors simultaneously.

In any case, I don’t think that “immune system and the testicles and ovaries” are proposed to be primary targets.  I think the model, such as it is, suggests that the primary infection damages nervous tissue and leads to an immune response against the nervous tissue components when people have a certain set of genetic tendencies.