You really do need to get all your animals rounded up and quarantined. If it really is an outbreak where you are and you continue to let them free roam and die, you could easily spread it to wildlife which can spread it to who knows where. Plus, if you don't know what an animal died from and it seems to be spreading, you NEED to burn the bodies or risk further infecting other things. Personally, auctions, especially "exotic" auctions can spread diseases from all over the world because there is no guarantee that proper quarantine was practiced and there have been cases of people catching rare diseases from animals imported from other countries. If you even visited with your friend wearing clothes or shoes that could have been contaminated, or wore your auction clothes into your barns, it's possible to carry in the pathogen to your flocks.