Addressing Foodborne Threats to Health Policies, Practices, and Global Coordination: Workshop Summary (2006) / Chapter Skim
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6 Reporting Foodborne Threats: The Case of Bovine Spongiform Encephalopathy (BSE)
6 Reporting Foodborne Threats: The Case of Bovine Spongiform Encephalopathy (BSE)
Pages 195-231
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Prusiner presents experimental evidence for the prion model of TSE and describes the etiology and diagnosis of vCJD and other human prion diseases. He emphasizes the differences between prion and viral illnesses -- most notably, that prions can arise spontaneously -- and observes that the mistaken equation of the 195
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government acted surprised by the finding, they should have expected such cattle based on the biology of the prion diseases. Perhaps the novel principles of disease that have emerged over the past two decades from investigations of prions (Prusiner, 2004b)
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In the sporadic and genetic forms of prion disease, prions arise spontaneously. In contrast, infectious prion diseases result from exposure to an exogenous source of prions.
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In contrast, the vast majority of prion diseases are initiated from within the host, in which prions arise spontaneously. Often the term prion infection is used synonymously with prion disease because once prions are formed spontaneously they can be transferred to another host and thus, are infectious.
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The Mad Cow Epidemic The world awoke to the dangers of prion disease in cows after the BSE outbreak began ravaging the British beef industry in the mid-1980s. The truly novel concepts emerging from prion science forced researchers and society to think in
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Despite the British government's early assurances to the contrary, mad cow disease proved transmissible to humans. In March 1996, Robert Will and his colleagues reported that 11 British teenagers and young adults had died of a variant of Creutzfeldt-Jakob disease (vCJD)
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Infectious Human Prion Diseases Prions from different sources have infected humans. Human prions have been transmitted to others both by ritualistic cannibalism and iatrogenic means.
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. Approaches to Prion Diseases Because prion diseases have aspects that resemble illnesses caused by viruses as noted above, many people use analogies to viruses when thinking about prions.
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Diagnosis of Prion Diseases The clinical diagnosis of human prion disease is often difficult until the patient shows profound signs of neurologic dysfunction (Roos et al., 1973; Will et al., 2004)
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. The CDI detected HuPrPSc with a sensitivity comparable to the bioassay for prion infectivity in Tg mice expressing chimeric human-mouse PrP.
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No reasonable human would knowingly expose himself or herself to prions as prion diseases are invariably fatal. In Europe, a policy was instituted four years ago of prion testing for all cattle destined for human consumption that are over 30 months of age.
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SURVEILLANCE AND PREVENTION OF vCJD AND BSE: THE AUSTRALIAN PERSPECTIVE Steven Collins, M.D.2 University of Melbourne, Parkville, Australia As an introduction to bovine spongiform encephalopathy (BSE) and its consequent zoonosis, variant Creutzfeldt-Jakob disease (vCJD)
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. Given the dramatic increase in BSE, in accordance with one of the recommendations of the Southwood enquiry, national surveillance for human prion diseases was prudently re
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In 1996, a new or variant form of CJD (vCJD) was reported by the National CJD Surveillance unit in Edinburgh, Scotland, with 10 younger adults and adolescents manifesting a phenotype hitherto not described (Will et al., 1996)
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Further, not only must we be alert to a possible secondary wave of vCJD, but given the unprecedented calamitous transmission of BSE to humans, we must also keep vigilant to the possibility of other cross-species transgressions from TSEs now apparently confined to animals, such as chronic wasting disease. Australia's National CJD Registry The Australian National CJD Registry (ANCJDR)
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TABLE 6-1 Cases of Transmissible Spongiform Encephalopathies (TSE) Reported to the Australian National CJD Registry (ANCJDR)
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From 1988, live cattle from the United Kingdom and any other country reporting BSE cannot be imported into Australia. Owners of animals imported from countries in which BSE is subsequently discovered can choose to place the imported animals under lifelong quarantine or have them slaughtered.
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Following a change in the OIE terrestrial animal health code, an additional 400 sick animals (including downer animals, those that die on the farm, and those slaughtered to contain a disease outbreak) are now tested for BSE by Western blot of brain specimens.
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The first and foremost function of public health is health protection. Table 6-5 lays out a well
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. TABLE 6-3 Functions and Core Programs Public Health Functions Core Program Areas · Population health assessment · Communicable disease prevention and control · Public health surveillance · Prevention of chronic diseases and injuries · Disease and injury prevention · Health development through life cycle · Health promotion · Environmental health · Health protection · Emergency preparedness SOURCE: National Advisory Committee on SARS and Public Health (2003)
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· Measures have been undertaken by animal health authorities, but do not result in complete avoidance of exposure. Prevent exposure.
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. Population Health Assessment and Decision Making in Uncertainty Since the first case of BSE and the subsequent first case report of vCJD some 10 years later, science and public policy have come a long way.
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As of March 2006, 160 cases of vCJD (National CJD Surveillance Unit UK, 2006) had been reported in the United Kingdom -- this in a country where it has been estimated that over 1 million infected cattle entered the human food chain (Ghani et al., 2000)
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Is it because of particular physiologic characteristics of the age group? Could it be that everyone is at equal risk, but that the incubation period varies?
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Reduce risk to humans from apparently healthy animals: · Remove and destroy specified risk materials (SRMs are the tissues that might contain or be contaminated by the SBOs) ; · Control animal feed security; and · Test where necessary and where it will improve safety, and consider that testing every animal may not lead to improved safety if it diverts resources from prevention.
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The flow of accurate analysis to senior policy makers in government is required to ensure that a realistic and thorough BSE risk assessment is conducted and uses evidence from both human and animal health perspectives. The risk assessment model should examine modes of population exposure to the BSE agent and must do so with consideration of the scientific evidence and the multiple requirements of all stakeholders.
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, eaten, or buried. Most animal 4Professor and Director, Center for Animal Health and Food Safety.
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Animal disease diagnostics in the United States are performed by state, university, and private laboratories that vary greatly in terms of their quality and capacity. About 12 of the 50 state animal diagnostic laboratories are linked in a pilot version of a national animal health laboratory network.
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Although animal diseases impose costs on farmers, they recognize that absence of disease (100 percent prevention and control) is not always the optimal economic strategy.
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For instance, controlled BSE challenge studies and accumulated BSE surveillance results demonstrate that young animals will test negative to all of our currently available tests even if exposed to BSE; this is because the disease takes years to create discernible damage to the central nervous system and for the disease agent, the prion protein, to accumulate to detectable levels. Consequently, testing only young cattle assures that all tests are negative but says nothing about the BSE status of a country.
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"What will we tell our grandchildren," he asked, "when we have spent all this money for a rare cattle disease with a relatively small human health impact, while at the same time we fail to take basic, proven public health measures for other diseases and conditions that impact the lives of millions because `we have no money.'" Lesson 7: High Health Status Is a Curse Once high health status is attained, the impetus for maintaining an animal health and public health infrastructure fades. We celebrate the successful eradica
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Strategies for Managing This Dilemma · Reframe surveillance discussions to focus on the purpose and the scientific basis for surveillance rather than the number of tests conducted; · Consider the entire farm-to-table food system when designing surveillance systems to support effective risk management for the end consumer and the nation; · Recognize that no one surveillance system fits all situations; the sampling design, sample size, and testing protocol must be adapted to the needs of each country in order to support optimal risk management; · Create more incentives for reporting disease to pull in more samples, rather than simply demanding testing through regulatory initiatives and penalties; · Develop a national animal identification system to support rapid response to disease outbreaks and long-term support for emerging disease detection; · Strengthen the national animal health laboratory system and increase its capacity, perhaps by providing federal resources to states tied to performance requirements and reporting so that all states can meet a minimum level of proficiency and quality; · Foster increased collaboration between biologic, medical, and social sciences in order to better understand the sociology and psychology of disease reporting and compliance. Biologic and medical sciences alone are not enough; · Focus on risk management rather than disease eradication or "zero risk"; · Adopt and implement science-based regulations for BSE and other emerging diseases building on international standards; · Build public-private partnerships to address emerging diseases on a global, rather than a national, scale; · Recognize that all animal health issues are public health issues because of
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2005. Highly bovine spongiform encephalopathy-sensitive transgenic mice confirm the essential restriction of infectivity to the nervous system in clinically diseased cattle.
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2006. Kuru in the 21st century -- an acquired human prion disease with very long incubation periods.
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2003. Diagnosis of prion diseases.
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1997. Identification of a prion protein epitope modulat ing transmission of bovine spongiform encephalopathy prions to transgenic mice.
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2004. Infectious and sporadic prion diseases.
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