Introduction

On December 23, 2003 the United States Department of Agriculture announced the preliminary diagnosis of Bovine spongiform encephalopathy (BSE), commonly known as "mad cow disease", in a nonambulatory dairy cow from Washington state. Two days later, the BSE World Reference Laboratory in Weybridge, England confirmed the diagnosis. Although no infected tissue from this cow is thought to have entered the food chain, the USDA began a recall of meat from the facility that processed the cow, and began tracking down herdmates and offspring of the infected animal. BSE gains media attention due to its economic impact on the agricultural industry, and its association with variant Creutzfeld-Jakob disease (vCJD), a fatal disease in humans.

BSE is a fatal degenerative neurological disease that affects cattle, and is thought to be caused by feeding scrapie-infected meat and bone meal to cattle. BSE was first diagnosed in Great Britain in 1986, and there have been over 180,000 confirmed cases of BSE in Great Britain since. BSE has occurred in several other European, Asian, and Middle Eastern counties and Canada. Consumption of neural tissue from BSE-infected cattle is associated with variant Creutzfeld-Jakob disease (vCJD), a fatal disease in humans. BSE and vCJD are members of a family of Transmissible Spongiform Encephalopathies (TSEs), a group of diseases with similar pathogenesis and microscopic lesions. TSEs affecting other animals include scrapie in sheep and goats, feline spongiform encephalopathy in domestic and exotic felines, chronic wasting disease in deer and elk, and transmissible mink encephalopathy in mink. The term scrapie is derived from one of the symptoms of the disease. Affected animals scrape off their hides against rocks or trees (left) apparently in response to uncontrollable itching.