BSE, that is bovine spongiform encephalopathy is a progressive, lethal central nervous system disease of cattle. It is characterized by the appearance in neurons in the brain of affected cattle of vacuoles, clear holes, that give the brain the appearance of a sponge -- this is where the term spongiform came from.

These are visible with an ordinary microscope. It is very similar to other Transmissible Spongiform Encephalopathies (TSEs) in animals. TSEs are diseases characterized by spongy degeneration of the brain with severe and fatal neurological signs and symptoms. BSE is one of several different forms of transmissible brain disease affecting a number of animal species.
Scrapie is a common disease in sheep and goats. Mink and North American mule deer and elk can contract TSEs. A neurological disease in household cats and in ruminant and feline species in zoos has been linked to BSE; most cases in such animals appear to have occurred in the UK.