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World Health Organization Consultation on Public Health Issues Related to Bovine Spongiform Encephalopathy and the Emergence of a New Variant of Creutzfeldt-Jakob Disease

At a World Health Organization (WHO) Consultation organized in Geneva on April 2-3, 1996, a group of international experts reviewed the public health issues related to bovine spongiform encephalopathy (BSE) and the emergence of a new variant of Creutzfeldt-Jakob Disease (V-CJD), as officially reported by the United Kingdom on March 20, 1996.

The Consultation made recommendations, based on the latest scientific information, to minimize transmission of BSE among animals and to reduce as completely as possible any exposure of humans to the BSE agent.

FINDINGS

Bovine Spongiform Encephalopathy

BSE is a transmissible spongiform encephalopathy (TSE) in cattle, which was first identified in the United Kingdom in 1986. It is one of a group of similar degenerative diseases that occur in several animal species. Transmission of BSE to cattle appears to have occurred by contaminated meat and bone meal in concentrate feed, sheep or cattle being the original source. The United Kingdom is the only country with a high incidence of the disease, and the epidemic there appears to have been due mainly to recycling of affected bovine material back to cattle before the ruminant (cattle, sheep, and goats) feed ban in July 1988 took effect. There is no evidence of either maternal or horizontal transmission of BSE.

The incidence of the disease is declining significantly in the United Kingdom, although the measures introduced have not thus far halted the epidemic. The worldwide distribution of BSE is not known precisely, but it has been reported at a much lower incidence than in the United Kingdom in native cattle in other European countries. In these latter countries only part of the BSE cases could be related to consumption of feed that might have been contaminated with the BSE agent.

Variant of Creutzfeldt-Jakob Disease

The group reviewed the clinical and pathologic data from the 10 cases in the United Kingdom. The disease has occurred at younger ages than is usual for classical CJD and shows several clinical and pathologic differences. Based on findings in these 10 cases, the group established a case definition to facilitate better surveillance, which is necessary to determine the incidence and distribution of this syndrome.

The group concluded that there is no definite link between BSE and V-CJD but that circumstantial evidence suggests exposure to BSE may be the most likely explanation. Further research on both diseases is urgently required.

Exposure to BSE has already been greatly reduced by measures taken in the United Kingdom.

RECOMMENDATIONS

Bovine Spongiform Encephalopathy

  1. No part or product of any animal that has shown signs of TSE should enter any food chain, human or animal. All countries must ensure the slaughter and safe disposal of TSE-affected animals so that TSE infectivity cannot enter any food chain. All countries should review their rendering procedures to ensure that they effectively inactivate TSE agents.

  2. All countries should establish continuous surveillance and compulsory notification for BSE according to recommendations established by the Office international des Epizooties in Paris. In the absence of surveillance data, the BSE status of a country must be considered as unknown.

  3. Countries should not permit tissues that are likely to contain the BSE agent to enter any food chain, human or animal.

  4. All countries should ban the use of ruminant tissues in ruminant feed.

  5. With respect to specific products:

    1. Tests on milk from BSE-infected animals have not shown any BSE infectivity, and there is evidence from other animal and human spongiform encephalopathies to suggest that milk will not transmit these diseases. Milk and milk products, even in countries with high incidence of BSE, are therefore considered safe.

    2. Gelatin in the food chain is considered to be safe. The usually applied manufacturing process has been demonstrated to significantly inactivate any residual infective activity that may have been present in source tissues.

  6. With respect to medicinal products:

    1. Removal and inactivation procedures contribute to the reduction of the risk of infection, but it must be recognized that the BSE agent is remarkably resistant to physico-chemical procedures that destroy the infectivity of common microorganisms.

    2. The importance of obtaining bovine materials destined for the pharmaceutical industry only from countries that have a surveillance system in place and that report either no or only sporadic cases of BSE is reiterated.

    3. Measures recommended to national health authorities to minimize the risk of transmitting the agent causing BSE through medicinal products, in particular parenteral products, which were developed at a WHO Consultation in 1991 (Bulletin of the World Health Organization1992;70:183-90), continue to be generally applicable.

    4. It is recommended that these measures be reviewed and, if necessary, strengthened as more information become available.

  7. Research on TSE should be promoted, especially on rapid diagnosis, agent characterization, and epidemiology of TSEs in humans and animals.

Variant of Creutzfeldt-Jakob Disease

  1. The full geographic distribution of V-CJD, although reported at present only in the United Kingdom, needs to be further investigated.

  2. While the most likely hypothesis at present for this newly recognized variant is exposure to the BSE agent, further data from scientific studies on these variant cases are urgently required. More monitoring and surveillance studies on all forms of CJD are required throughout the world, modeled on current European collaborative studies.

  3. Exposure to BSE from beef and beef products has already been substantially reduced by the measures taken in the United Kingdom. Exposure to BSE is considered lower in other countries. The group considered that implementation of their recommendations will ensure that any continuing risk of exposure to BSE in beef and beef products will be reduced to a minimum.

As surveillance worldwide is increased for both BSE and V-CJD, more information will become available in the coming months. WHO will keep these developments under review and update the recommendations as appropriate.

Adapted from Weekly Epidemiological Record 1996;71(no.15) (in press). Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: In the United States, the U.S. Department of Agriculture (USDA) has conducted active surveillance for BSE in cattle since 1990 and has not detected any cases. Nonetheless, because of the concern that V-CJD in the United Kingdom might possibly be linked to BSE, additional safety measures are being instituted, including discontinuation of the use of ruminant tissue in ruminant feeds.

CDC conducts surveillance for CJD through examination of death certificate data for U.S. residents for whom CJD was listed as one of the multiple causes of death (1). Based on this surveillance, during 1979-1993, the annual incidence of CJD remained stable at approximately one case per million persons. In the United Kingdom, five of eight patients who died with V-CJD since May 1995 were aged less than 30 years; in comparison, in the United States, CJD deaths in this age group remain extremely rare ( less than 5 cases per billion per year).

CDC is working with the Council of State and Territorial Epidemiologists to consider expansion of current CJD surveillance. On April 8, an interagency meeting including representatives from CDC, the National Institutes of Health, the Food and Drug Administration, USDA, and the U.S. Department of Defense was held to disseminate conclusions from the WHO consultation and to coordinate preventive activities for BSE and CJD. CDC is working with its four established Emerging Infections Disease Programs (Minnesota; Oregon; New Haven, Connecticut; and the San Francisco Bay area, California), the Georgia Department of Human Resources, and the Atlanta Metropolitan Active Surveillance Program to pilot enhanced surveillance efforts for CJD, including an active search for V-CJD as described in the United Kingdom (2).

References

  1. Holman RC, Khan AS, Kent J, Strine TW, Schonberger LB. Epidemiology of Creutzfeldt-Jakob disease in the United States, 1979-1990: analysis of national mortality data. Neuroepidemiology 1995;14:174-81.

  2. Will RG, Ironside JW, Zeibler M, et al. A new variant of Creutzfeldt-Jakob disease in the UK. Lancet 1996;347:921-5.



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