Academic journal article Bulletin of the World Health Organization

The Epidemics of Bovine Spongiform Encephalopathy and Variant Creutzfeldt-Jakob Disease: Current Status and Future Prospects. (Public Health Reviews)

Academic journal article Bulletin of the World Health Organization

The Epidemics of Bovine Spongiform Encephalopathy and Variant Creutzfeldt-Jakob Disease: Current Status and Future Prospects. (Public Health Reviews)

Article excerpt

Voir page 129 le resume en francais. En la pagino 129 figura un resumen on espanol.

Introduction

Variant Creutzfeldt-Jakob disease (vCJD) has so far been diagnosed in fewer than 150 people. The epidemic has attracted considerable attention, which, in terms of global threats to public health, some might consider to be disproportionate to its size. There are several reasons for such attention. First, vCJD appears to be a new disease. Second, although the present number of cases is small, the average incubation period is not known--it may be more than 10 years, and therefore many more people may be diagnosed in the coming years. Third, the disease is widely thought to be caused by a relatively newly recognized class of infectious agent, the prion, which has several notable characteristics--not least its ability to survive sterilizing processes that inactivate most biological agents. Fourth, the disease has predominantly affected young people, and its clinical course is relentless. The disease is currently untreatable, very distressing, and uniformly fatal. Fifth, a high proportion of the United Kingdom population, as well as visitors to the country and people who have consumed bovine products exported from the United Kingdom, may have been exposed to the agent. Sixth, the epidemic of bovine spongiform encephalopathy (BSE) has had a substantial impact on world trade and has raised concern about the safety of a widely consumed food product, beef. Seventh, in the United Kingdom alone, the cost of the BSE epidemic has exceeded US$ 6 billion, and substantial additional costs will continue to be incurred in the future, not least in guarding against the possibility of iatrogenic transmission of vCJD.

This review summarizes the evolution of the bovine and human epidemics, speculates on their future development, and summarizes some of the outstanding issues.

Origins of the BSE epidemic

Although the first case of BSE was identified in the United Kingdom in 1986, it is likely that some cases occurred earlier than this but were not detected and that the origin of the epidemic probably dates back to the 1970s. What caused the first case of BSE, why the epidemic started in the United Kingdom, and why it started when it did are questions that are unresolved and may remain so. What is clearer, however, is that the epidemic was caused by the practice of feeding cattle the waste parts of other cattle, which were not used for human consumption, in the form of meat and bone meal (MBM) after the bovine material had been rendered (1, 2). Rendering is the process whereby the waste parts of cattle are heated to separate out the fat and protein, so that the latter can be incorporated into MBM, a high-protein supplement feed. Studies showed that the rendering processes that were in use in the 1970s and 1980s in the United Kingdom, and in many other countries, may not have completely inactivated the infective agent (3).

Once the BSE agent had been introduced into this recycling process that transferred it from bovine to bovine, cases increased in number to cause the epidemic of the disease in the United Kingdom. In many respects, there are similarities with the epidemic of kuru (a human form of transmissible spongiform encephalopathy (TSE)) that affected several thousand people in a remote tribe in Papua New Guinea (see below).

Although it is reasonably certain that MBM caused the epidemic in the United Kingdom once the infective agent had entered cattle, how the infective agent got into cattle in the first place is far less clear. There are many competing hypotheses but two of the most plausible are that the initial case arose: sporadically in a bovine, and that tissue from this animal entered the rendering process (consequently, the infective agent was transferred to other cattle through feed); or through a cattle-adapted strain of the sheep TSE, scrapie, which entered the rendering process in the waste parts of a sheep (as sheep waste was also rendered and incorporated into MBM). …

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