Onset of clinical signs is insidious with subtle behavioral changes or occasional collapse. As the disease progresses, animals show signs of pruritis by biting, rubbing or kicking at their bodies. Diseased animals also have gait abnormalities including a stilted stride, incomplete flexion of the hock, weakness and abnormal postures. These animals may also show signs of hyper excitability. In the last 4-5 weeks of the disease, animals become anorexic and lose body weight.
Animals usually die within a couple of months of the onset of clinical signs.
It should be noted that it is difficult to differentiate between the clinical signs of sheep infected with BSE and those infected with scrapie. The full mechanisms of transmission are not known. The prion protein is later found in the spleen and other lymph nodes. It is thought that it travels by blood to reach these sites but the exact mechanism is not known. The protein accumulates in the central nervous system.