MAD COW DISEASE.

Mad cow disease or bovine spongiform encephalopathy (BSE) was first identified in the United Kingdom in November 1986. The disease is one of a family of neurodegenerative diseases known as transmissible spongiform encephalopathies, which cause deterioration of cells in the brain and eventual death. By January 2005 more than 182,000 clinical cases of BSE had been confirmed in cattle in Great Britain, with epidemics also occurring on a smaller scale in other European countries including Northern Ireland, the Republic of Ireland, Switzerland, Portugal, and France. Worldwide cases have been confirmed as far away as Canada, the United States, and Japan. The economic impact of BSE in badly affected countries has been great, with the worldwide export ban imposed on the United Kingdom by the European Union between 1996 and 1999 having a long-lasting effect on the cattle industry in that country. In tandem, there has been a drop in consumer confidence, not only in beef products but also in the overall safety of food, triggered by other disease outbreaks caused by salmonella and other bacterial contamination. To combat this situation, the Food Standards Agency was formed as an independent food safety watchdog in 2000 to protect the public's health and consumer interests in relation to food.

BSE is thought to have originated in cattle from supplementary feed containing meat and bone meal (MBM) contaminated by a scrapie-like agent derived from sheep or cattle, although much debate continues over its origin. In the United Kingdom the disease was made notifiable in June 1988 and in July 1988 a ban on the use of ruminant-based MBM in cattle feed came into force in Great Britain. Although the ban did not prevent all infections and cases in animals born after 1988, the number of cases of BSE in Great Britain has continued to decline, demonstrating that MBM feeding practices had been the major route of transmission. However, even after stricter enforcement of the ban came into place in 1996, cases have still occurred in animals born after this time (known as Born After the Real Ban or BARBs) with more than one hundred such cases reported as of 2006. Extensive epidemiological investigations are under way for these BARB cases to identify remaining routes of transmission.

The appearance of BSE in cattle, while of veterinary, agricultural, and economic concern, was initially not thought to pose a threat to human health because of its similarity to scrapie, a disease in sheep that has been endemic in most parts of the world for more than two hundred years. This was demonstrated politically by the now-infamous picture of then–agriculture minister John Gummer feeding a hamburger to his young daughter. However this optimism was shattered in 1996 when the U.K. government announced a possible link between BSE and a new variant of Creutzfeldt-Jakob disease (vCJD) in humans. Since this time, scientific evidence in support of the hypothesis that vCJD is a direct consequence of exposure to BSE has been strengthened. In the United Kingdom alone it is estimated that more than two million infected cattle were slaughtered for human consumption, indicating widespread exposure of the population to the infectious agent. A variety of measures have been put in place to reduce exposure, including the ban on the use of high-risk materials (including the brain and spinal cord) and animals over thirty months of age in food production.

By 1 July 2005, 150 human deaths from vCJD had been reported in the United Kingdom with a further six patients with probable cases still alive. In addition cases have been reported in France, Italy, Republic of Ireland, the United States, Canada, Saudi Arabia, Portugal, and Japan. While the number of cases remains relatively small, concern has now shifted to the possibility of ongoing transmission through blood transfusions and surgical instruments given the potentially large number of people who could be harboring subclinical forms of the disease. A blood transfusion has been formally identified as the most probable source of infection for one vCJD case, and in addition signs of infection have been identified in the spleen of another patient who died from other causes but who was known to have received blood from a vCJD case. A number of measures to protect blood supplies both within the United Kingdom and elsewhere have been introduced over the past ten years, including leucodepletion of blood, which is thought to reduce the risk of transmitting infection by about 40 percent, and a ban on donors who have themselves received a blood transfusion. Transmission via surgical instruments has not been documented to date but remains a potential risk. Because of the many uncertainties about these secondary routes of transmission, the potential future scale of the outbreak is unclear. However the BSE and vCJD epidemics are likely to remain a cause for government and public concern for several years.

See alsoAgriculture; Diet and Nutrition; Public Health .

BIBLIOGRAPHY

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Azra Ghani