Causes
Scientists believe that BSE is most often spread through the practice of feeding cattle various meats (rendered material) from slaughtered animals such as sheep, goats, and other cattle. During this process, an abnormal protein that is linked to BSE can spread from a slaughtered diseased animal to a healthy one. This abnormal protein, called a prion, can withstand high temperatures and does not get destroyed during the rendering procedure. Since the incubation period for BSE is so long, it is possible for an infected animal to enter the food chain before the symptoms appear.
All proteins are long molecules folded up into particular shapes. A prion is folded differently from the normal protein. What's more, it has the ability to make normal proteins that touch it fold in the same abnormal way. When this happens, the proteins, which are normally in liquid form, begin to solidify within the cells. The cells most often infected are the brain cells. The resulting solidification of the proteins causes the infected brain tissue to look like a sponge with several tiny holes, hence the name spongiform encephalopathy.
This is a completely new form of disease. It is caused by an infectious agent that's not alive but is capable of multiplying.