Bovine Spongiform Encephalopathy

Bovine spongiform encephalopathy (BSE) is a fatal neurodegenerative disease, caused by a prion, that mainly affects cattle. Other ruminant species, cats, non-human primates and humans are occasionally affected; this disease is called feline spongiform encephalopathy (FSE) in cats, and variant Creutzfeldt-Jakob disease (vCJD) in people. BSE is a relatively new disease that was first reported in the United Kingdom in the 1980s. It is spread by ingestion; animals or humans become infected when they eat prion-containing tissues from an infected animal. Cooking and standard disinfection procedures do not destroy this agent. Infected animals or people do not become ill for years; however, the disease is always progressive and fatal once the symptoms develop. The origins of BSE are unknown; however, the recycling of ruminant proteins in ruminant feed amplified this prion and caused an explosive epidemic in the U.K in the 1980s and 1990s. This epidemic peaked in 1992, with almost 1,000 new cases diagnosed each week. Although cases continue to be detected, control measures have greatly decreased their prevalence; fewer than 15 bovine cases were reported annually in the U.K. during 2009-2011. BSE also spread to many European countries, North America, parts of Asia, and possibly other areas of the world. The presence of BSE in a country can result in trade sanctions, as well as increased public concern about meat safety. Many nations, including the U.S., conduct control and surveillance programs. Many countries have also passed new regulations to prevent BSE-containing tissues from entering human or animal food supplies. As a result of increased surveillance, BSE prions that differ from the prion causing ‘classical’ BSE have been identified at very low levels in cattle populations. Currently, it is thought that these “atypical” prions may represent a spontaneous form of prion disease. Some experiments suggest that an atypical prion might have given rise to the BSE epizootic when it was amplified in cattle feed.