Epidemiology and control of bovine spongiform encephalopathy (BSE).

BSE is a new disease of cattle. The first clinical case occurred in April 1985 but the existence of a new disease was first confirmed microscopically in November 1986. Epidemiological studies show that cattle suddenly became effectively exposed to a scrapie-like agent in ruminant-derived feed in the form of meat and bone meal in 1981/2. Most cases have occurred in Holstein Friesian dairy cattle and have been exposed as calves. There is no evidence that cattle to cattle transmission sufficient to maintain the epidemic occurs. The principle animal health control measures are bans on the feeding of ruminant derived protein to ruminant animals and on the use of specified bovine offals (SBO) for feeding to any species of animal or birds. Human health is protected by compulsory slaughter and destruction of suspect animals, and a ban on the use of their milk, and by prohibiting the use of SBO in food. The SBO are those tissues which, in clinically healthy cattle incubating BSE, might conceivably harbour infectivity. The effectiveness of the bans is supported by recent evidence of a decline in the cattle epidemic. There is no evidence that BSE is a zoonosis.