It is spread through milk, but also faeces in cattle. The body is only susceptible to the infection when young, but it takes a long time to develop signs of the disease. Once they do, however, it is an intense diarrhoea and wasting, with shedding of vast numbers of the bacteria for calves to pick up. Thus separating calves immediately stops them ingesting any colostrum from infected cows and being in contact with any of their dung.
It works similarly in goats and sheep but often without the diarrhoea.
I think it would probably be kinder to send your goats before they got ill, because I cant imagine the slow wasting to be pleasant, and I know a Crohns sufferer, and am allergic to cows milk myself, so suspect they must feel similar cramping due to the disease, and although animals hide illness well, i suspect its not a nice one to go through. As I think this would be best for the 'positive' goats, i would advise sooner than later, perhaps preventing spread to the others.
It is then up to you whether to vaccinate. If you have older goats, they are likely to already have it incubating, or not be affected, theyre much less likely to have just picked it up, but if you have kids, they may have just become infected, or be just about to if the bugs are there. If you were going to vaccinate, it may be worth doing the youngstock, but they may all be ok.
Either way, you will need to test repeatedly as they all age to see that there aren't more becoming positive.
Its a horrible disease and only being ruthless will sort it for good.
Ps, I imagine the tip from the dairy on 'snatch calving' would help in goats too - you take the babies as soon as they are born to a clean area, preferably before they hit the ground