Carrier!
I had delivered some new sheep couple of weeks ago and put them on a nice field of grass(ish). Ewes & lambs! 1 DAY later one had a lump, I thought "can't be!" Within the next few days all but 1 are infected with lumps and crusts!
Fortunately it showed earlier so they didn't go with mine who have to go to a tup in another week or so.
Old owner contacted me and told me she'd discovered it in her flock and for me to keep watch!
Orf is one of those things, once got, it's there to come and get you when it wants!