As FW says, CLA is a concern. Make sure you capture everything that touches the exudate - cloths, needles, knives, containers, whatever - and anything you are not taking to the lab, dispose of with great care. I'd suggest burning but don't in fact know if there'd be a risk of its spreading this way.
CLA is most often spread by shearers, the clippers nick an abcess on one sheep then pass the infection to the rest of the flock - and the next flock too, if the shearer is less than 100% in his / her hygiene routine.