Yep, it will just run it's course. If they have a lick in with them in th field, that will certainly spread it, but feed troughs/hay racks will too. However I would not worry too much, most of my youngstock went through with it during the summer. You cannot disinfect ALL fence posts, tree trunks etc... so just watch and if any sheep gets too down with it and looks really miserable you may put some nappy rash cream/sudo cream or dare I say purple/blue spray on it to help it heal. Sometimes vets recommend an AB injection to ward of secondary bacterial infection, but I have never injected any for orf.