Academic journal article Bulletin of the World Health Organization

Bovine Spongiform Encephalopathy in the United Kingdom: Memorandum from a WHO Meeting

Academic journal article Bulletin of the World Health Organization

Bovine Spongiform Encephalopathy in the United Kingdom: Memorandum from a WHO Meeting

Article excerpt

The meeting was convened following a request by members of the WHO Executive Board in January 1993 expressing some concern regarding the continuously increased incidence of bovine spongiform encephalopathy (BSE) in the United Kingdom during 1992 and early 1993, as reported in various media, and the occurrence of a case of Creutzfeldt-Jakob disease (CJD) in a person occupationally exposed to a cow with BSE.

Update on research

Until 1985, six transmissible spongiform encephalopathies (TSE) were known, three in man and three in animals (i.e., scrapie of sheep and goats, chronic wasting disease of some species of captive wild deer (only in the USA), and transmissible mink encephalopathy (TME)); the last named has never occurred in the British Isles. From 1985 to May 1993, nine further species have developed naturally occurring TSE, five species of captive wild ungulates (total confirmed cases, 13), domestic cats (41), puma (1), cheetah (2), and moufflon, besides bovine spongiform encephalopathy in cattle. Only the last has had a significant incidence, occurring in indigenous cattle only in the United Kingdom (>92000 cases), Ireland (69), Switzerland (34), and France (5).

The research programme on BSE and other TSEs is very large and has numerous funding bodies in the United Kingdom, with the greatest effort placed at the Central Veterinary Laboratory, Weybridge, and the Institute for Animal Health, Neuropathogenesis Unit, in Edinburgh. Funding has recently been extended to other institutes and includes inputs from the European Community (EC) and the U.K. Agriculture and Food and Medical Research Councils as well as the Departments of Health and Industry. Both animal and human health aspects are under investigation. Outside Europe, and particularly in the USA, there is research and surveillance for TSE in U.S. cattle, including transmission, molecular chemistry, and genetic studies.

Transmission studies

Transmission studies in the United Kingdom had the following objectives:

- to determine the experimental host range of BSE; - to assay the infectivity of tissues of cattle confirmed - to have BSE; - to determine the occurrence and incidence of - maternal transmission; - to confirm that bovine embryos derived from - BSE-confirmed cattle in the clinical phase of disease

do not transmit BSE to the recipient offspring

or their surrogate dams; - to determine the infectivity of brain from other

species recently affected by spongiform encephalopathy(SE).

Spongiform encephalopathy has been successfully transmitted to mice, cattle, sheep, goats, pigs, marmosets, and mink (data not published) after parenteral administration of brain from cattle confirmed to have BSE. Transmission has not resulted in challenged hamsters in the United Kingdom. Parenteral and oral challenge experiments in poultry remained negative (as at May 1993), following administration of infected material in June/July 1990.

Oral or feeding exposure to infected material from BSE-confirmed cattle was attempted and successful in mice, sheep and goats. Cattle that received cattle placenta oro-nasally and brain orally, and pigs that received BSE brain orally remained healthy (as at May 1993); the study in cattle (using placenta) commenced in November/December 1989 and the study in pigs in May/June 1990.

The successful transmission via the parenteral route in pigs using massive doses (and multiple parenteral routes) resulted in seven transmissions out of eight (two other pigs died of intercurrent disease at a young age). The range of incubation was from about 17 months to 37 months (data not published).

The results of the marmoset study have been published recently.(a) Two marmosets were each parenterally challenged with brain from a sheep with scrapie or cow brains with BSE. The mean incubation period was longer in both these instances (about 41 months with scrapie and 49 months with BSE) than with human TSE material or that passaged via mannosets (<30 months). …

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