BSE and vCJD are among a group of diseases known as transmissible spongiform encephalopathies (TSE). Currently, there are no therapies or vaccines to treat TSEs, and a definitive diagnosis can only be made from a post mortem examination of the brain. The infective agent that gives rise to TSEs is generally thought to be a malformed protein, called a prion,which causes normal molecules of the same protein in the brain to become malformed. Prions cannot be killed by conventional heat, irradiation, or chemical disinfection and sterilization procedures. The precise amount of material needed to cause disease is unknown but is generally thought to be very small. TSE prions accumulate in central nervous system tissue—specifically the brain, spinal cord, and eye—but are also present in other body tissues of infected humans and animals. Other TSEs include Creutzfeldt-Jacob disease (in humans), scrapie (in sheep), transmissible mink encephalopathy, and chronic wasting disease (in elk and deer). The original source of BSE is not known with certainty. However, evidence suggests that the practice of recycling the remains of diseased animals, specifically scrapie-infected sheep, into feed for livestock, including cattle, was responsible for the emergence and spread of BSE in the United Kingdom. In 1988, the United Kingdom banned the practice of feeding ruminant-derived protein to ruminants. Following this ban, the number of new cases of BSE-infected cattle declined from a high in 1992 of 32,280 new cases to a total of 1,312 cases in 2000, and to 526 cases as of September 30, 2001. About 2,500 cases of BSE have appeared elsewhere in 18 other European countries, as well as Oman, Canada, the Falkland Islands, and Japan, as a result of the exportation of contaminated feed and cattle (see fig. 1). The one BSE-infected cow found in Canada had been imported and was destroyed without entering the animal or human food chains. The BSE-infected cattle found in Oman (two animals) and the Falkland Islands (one animal) had also been imported. In 1996, experts in the United Kingdom reported the first cases of vCJD. They believed the victims contracted it by eating beef contaminated by central nervous system tissue from BSE-infected cattle. Although contamination of meat with central nervous system tissue could occur in many ways during the slaughtering and processing of cattle, the major suspect in these cases was meat removed by a system that mechanically recovered (by squeezing under pressure) the remaining meat left on carcasses after all accessible meat has been removed by knife. Prior to December 1995, when the United Kingdom banned the practice, mechanically recovered meat, which was included in many cooked meat products such as sausages, could legally have contained spinal cords. While scientists believe that at least several hundred thousand people may have eaten BSE-infective tissue, many believe vCJD is difficult to contract. As of November 2001, 112 people have had vCJD, of whom just over 100 had died, nearly all in the United Kingdom. Most vCJD victims have been young—the average age at death was 28—and half died within 13 months from the time they first showed symptoms. As figure 2 shows, cattle provide meat and a wide array of consumer products. Many of these products may pose at least a theoretical risk for BSE infection. For example, dietary supplements, vaccines, cosmetics, and surgical replacement tissue, as well as gelatin, are produced from bovine carcasses, central nervous system tissue, and blood. The rendering industry in the United States and elsewhere recycles animals and animal tissues considered unfit for human consumption into, among other things, animal feed; diseased animals are routinely part of such recycling. The United States trades extensively in animals and the full range of animal products. No test for BSE or TSE infectivity has been proven adequate for diagnosis in humans or animals before symptoms appear or for screening blood and other products. Tests to detect proteins from cattle in animal feed do not distinguish between milk and blood proteins that are allowed and meat and bone proteins that are not. Furthermore, methods to test animal feeds are based on the analysis of genetic material, bone, and protein, all of which are degraded or destroyed in the rendering process. The lack of unique genetic material associated with BSE prions has led scientists to look for other biological markers for the disease, such as accumulations of abnormal forms of the prion protein in various tissues. Development of valid, sensitive, rapid, and reliable tests for live animals is difficult because the specific agent has not been fully identified and elicits no detectable immune response. Furthermore, efforts are hampered by the limited scientific understanding of BSE and other TSEs, including when during the incubation period infectivity appears, what mechanism causes infection, and whether infectivity is ever present in blood. Four federal agencies are primarily responsible for overseeing the many imported and domestic products that could pose a risk of BSE and for surveillance programs designed to detect and monitor animal and human diseases: The U.S. Customs Service screens all goods entering the country to enforce Customs laws and laws for 40 other agencies. USDA’s Animal and Plant Health Inspection Service monitors the health of domestic animals and screens imported animals and other products to protect animal health. USDA’s Food Safety Inspection Service monitors the safety of imported and domestically produced meat, poultry, and some egg products. FDA, within the Department of Health and Human Services (HHS), monitors the safety of all other foreign and domestic food products (including dietary supplements and animal feed), as well as vaccines for humans, drugs, cosmetics, medical devices, and the human blood supply. In addition, two other HHS agencies—the Centers for Disease Control and Prevention and the National Institutes of Health—monitor human health to detect vCJD should it appear and conduct research to better understand TSEs and the prions thought to cause them. In August 1997, FDA banned potentially BSE-infective animal proteins in feed for cattle and other ruminants. Proteins are added to feed to promote animal growth and can be derived from a number of sources, including animal meat and bone meal, fishmeal, and plant products. The feed ban prohibits the use of most animal-derived proteins in cattle feed. It also requires that, among other things, feed and feed ingredients that contain the prohibited proteins be labeled “Do not feed to cattle or other ruminants;” firms that handle both prohibited and nonprohibited feed and feed ingredients have procedures to ensure that the two are not commingled; and firms maintain records sufficient to track feed materials through their receipt and disposition for certain periods. The ban excludes animal blood and blood products, gelatin, plate waste, milk and milk protein, and protein derived from pigs and horses (and other equines). Renderers, feed manufacturers and blenders, and feed distributors are subject to the ban. Recent research on the ability of animals to be “silent” carriers of TSEs from another species raises questions about the advisability of including in feed for cattle, or other ruminants, proteins from animals such as pigs and horses that are currently not thought to be susceptible to BSE and other TSEs, according to researchers at the National Institutes of Health. Specifically, in November 2001 these researchers reported that even though mice experimentally infected with hamster scrapie did not develop clinical disease, infectivity persisted in the brains and spleens of the mice throughout their life spans. Although available laboratory methods were not sufficiently sensitive to detect the infectivity in these mice, the researchers could infect other mice and hamsters with tissue from the original asymptomatic mice. The European Commission—the executive and legislative body of the European Union— has had its Scientific Steering Committeeconduct assessments of the geographical risk of BSE for countries that requested an assessment. Between July 2000 and November 2001 these scientific experts issued assessments for 49 countries, including the United States, which the experts stated was unlikely to have BSE, but they also stated that the possibility could not be excluded. BSE differs greatly from foot and mouth disease (FMD). FMD is a highly contagious viral disease that primarily affects cloven-hoofed animals, including cattle, sheep, swine, and goats, and last appeared in the United States in 1929. In contrast to BSE, FMD does not threaten humans, rarely causes death in afflicted animals, and has an incubation period of 24 hours to 21 days. In addition, the virus that causes FMD can be killed using standard sterilization procedures. This report deals only with BSE. We also have a study underway, to be issued later in 2002, of federal measures to control the threat FMD may pose to U.S. livestock. The continuing absence of BSE in the United States today cannot be sufficiently ensured by current federal prevention efforts. The introduction and spread of BSE in the United States could stem from cattle and cattle- derived products imported from countries that subsequently developed BSE and from gaps in import controls, animal testing, and feed ban enforcement. As a result of these problems, consumers may unknowingly eat foods that contain central nervous system tissue from a diseased animal. Since 1989 and as recently as 2001, USDA and FDA have identified countries with BSE or at risk for BSE and issued import restrictions on ruminant-derived material from those countries. Figure 3 presents a timeline of the actions taken by USDA and FDA during that period. Figure 4 shows the countries on which the United States currently imposes trade restrictions for BSE-risk items.