Tissue samples were collected from all sheep, including intercurrent deaths, immediately following euthanasia. The brain was divided in half longitudinally, and half fixed in neutral buffered formalin (NBF), whilst the other half was frozen at -80 oC. Samples of palatine tonsil, spleen, ileal Peyer’s patch, mesenteric lymph node and prescapular lymph node were also fixed in NBF, and frozen at -80 oC, prior to further analysis. All frozen samples were collected using separate disposable instruments and using aseptic precautions.