Canada has also confirmed the disease in dairy cows imported from Britain. BSE has not been officially confirmed in the United States or any other major milk-producing country. The causes of BSE are still currently unknown, but much evidence suggests that prions, mutated forms of a normal protein are the cause. Just how prions cause the disease symptoms remains unclear. Prions are produced in nerve cells, white blood cells, muscle cells, and the cells of many other tissues.
Signs show that the gene coding for the prion protein undergoes a spontaneous mutation.
The gene then codes for the abnormal, infective form of the protein. A small number of mutant cells producing a small amount of prion protein can initiate a progressive infection. Recent research suggests that this occurs because the abnormal protein can transform normal molecules by causing them to change their configuration. Affected animals exhibit symptoms that include the loss of coordination and a staggering gait, as well as showing signs of senility, including lack of interest in their surroundings, the abandonment of routine habits, disinterest in feed and water, and unpredictable behavior. Death is the final step.