Do you have a lot of thistles around? Lambs noses can get pricked by the spikes, then that becomes infected with orf. It looks pretty much like orf, but anyway, treat it the same, NOT poking around at it (because it's sore, and all you'll do is spread it further including to you). Spraying with blue spray will prevent the pustules from secondary infection, but does nothing for the orf. When you are spraying around the mouth and near the eyes, take care to cover both from the spray. We haven't had orf for donkey's years so I can't remember how or if we treated it, as it's self limiting