Be careful that you don't get that on your skin or you will have it.  We had that in the late 90's.  We did nothing and the sheep built up their own immunity to it.  Biggest problem with it in lambs is they don't want to nurse because it hurts. 

There is a vaccine, I've been told that once you start down that road you have to keep vaccinating annually.  Can't swear that it's true.  All I know we did nothing, suffered through it for a year and the problem went away.  We closed up our flock at that time too just for that reason.  Did you bring in new ewes in the last year?