Multiple sclerosis and a little-known sheep disease

J.K.Rowling of the Harry Potter books fame recently announced that she was funding a research center in Scotland primarily for multiple sclerosis (which her mother died of), but also for other degenerative neurological
diseases.
MS is a disease of northern climes: where you were born and lived for the first fifteen years of your life determines your susceptibility to MS.
Remember Dr. Sigurdsson, the medical examiner for Iceland during WWII, who came up with the concept of slow viruses, i.e., viral (and more recently, prion, diseases that take a long time to develop into a full-blown disease, e.g., AIDS, mad cow disease - BSE).
Iceland was, at the time, suffering financially from what appeared to be two new sheep diseases: one that caused pneumonia (maedi - coughing), and another (visna - wasting) which caused wasting, tremors, blindness, paralysis of the hind limbs, and ultimately, death. Dr. S. determined that the two diseases were actually caused by the same slow lentivirus (which has been found to be related to the modern slow virus disease, AIDS).
Maedi-Visna (MV) was introduced into Iceland during the 1930's by the importation of diseased sheep from Germany. Dr. S. also remarked how similar MV was to MS - similar brain and neurological damage and symptoms.
The first documented human case of MS (a young woman) appeared in Holland during the mid-1700's, which makes it obvious that MV has been around for quite some time in some Dutch/German flocks of sheep. Don't forget that people and their animals did not move around much back then. What may have began and remained for years as a small, isolated-to-one-or-two-small valleys disease, started to become a world-wide disease with the large increase of movement of animals to different countries.
Yet when I googled MV disease and came up with mainly British articles, I got the somewhat startling info that MV had 1st presented itself in two widely different places: in South Africa and Montana in the US some eighty years ago. Using simple arithmetic I worked out that these two outbreaks also began in the 1930's, just like Iceland's. And, at least in South Africa, there is a direct link to Holland (and probably Germany), as the country was settled by Dutch settlers, who, obviously, would have brought, or bought, sheep from their country with them. Now there aren't any sheep indigenous to Montana and so I am assuming that German or Dutch settlers also brought or bought sheep from their homeland too, thus introducing MV disease into the US.
The British are concerned about this disease since it is new to the UK,and we do have a lot of sheep in Wales and Scotland, where this is a major source of income in wet, difficult mountainous areas; there were only 3 recorded cases two years ago, but there were 11 cases last year, and so companies are trying to find a vaccine for this retroviral disease (which given how difficult it has been to try and find a vaccine for the related retroviral disease, AIDS, may well prove to be impossible.
But if MS is the human equivalent to MV, why aren't researchers looking for a vaccine for MS too?