Bovine Spongiform Encephalopathy Health Article

BOVINE SPONGIFORM ENCEPHALOPATHY

Few more challenging food safety issues exist today than that of bovine spongiform encephalopathy (BSE) and the human form of the disease, variant Creutzfeldt-Jakob disease (vCJD). While vCJD remains rare at this time, the lack of a screening diagnostic test, uncertainty about the extent of exposure to the agent among humans and animals, the long incubation period, and the resulting devastating and inevitably fatal disease combine to create a situation of extreme difficulty for those responsible for public-policy development. The true extent of the unfolding epidemic is unknown, and since the largest exposures to BSE occurred before the relationship to a human disease was recognized, the full impact on human health may not be known for many years to come. This makes it difficult to determine appropriate actions to take to protect the consumer.

THE EPIDEMIC OF BSE

BSE appeared as a completely novel disease of cattle in the United Kingdom (UK), the first known case being diagnosed retrospectively in 1985. By 1986, BSE was recognized as a transmissible spongiform encephalopathy (TSE) of cattle and considered to be analogous to scrapie, a disease of sheep that is not known to cause human disease. Regardless, investigations were conducted to determine how it was being transmitted among cattle. These studies determined that protein supplement feeds made with meat and bone meal (MBM) were the most likely source of the disease. MBM is extracted from cattle and sheep carcasses through a long cooking process called rendering. Rendering is an established practice, used since the turn of the twentieth century. Through rendering, any tissue remaining on animal carcasses after removal of principle tissues is converted into a cake-like material that is used in multiple industries, including the production of protein supplements for animal feeding. Recycling of the agent through rendering led to the rapid and diffuse spreading of BSE throughout most of the United Kingdom (see Figure 1).

Cattle feed sold in the European market spread the disease further. The first cases outside of the UK appeared in 1989 in the Republic of Ireland. By 1990, two other countries (Portugal and Switzerland) were affected, and France reported its first case in 1992. As of December 2000, eleven European countries outside of the UK had reports of BSE in their national herds (Republic of Ireland, Switzerland, Portugal, France, Belgium, Luxembourg, Netherlands, Liechtenstein; and in 2000, Denmark, Spain, and Germany). Three other countries (Canada, Oman, and Maldives Islands) have reported cases, but only in imported cattle. The UK reported approximately 180,000 cases (as of December 2000), with just over 1,300 BSE cases reported elsewhere.