Public summary of meeting on
27th/28th April 1998

The Spongiform Encephalopathy Advisory Committee (SEAC) met on 27/28 April 1998 at Frensham Pond Hotel, Surrey. The majority of the meeting was devoted to a workshop to review the approaches, methodologies and current level of knowledge of key variables, which are central to the evaluation of risk to humans and animals from exposure to BSE.

Additional scientists from the Royal Society, the Royal Statistical Society, the European Commission's scientific advisory groups, and other risk analysts and statisticians participated in the workshop.

In the first session the meeting considered different approaches to BSE risk assessment and recognised that they now had much in common. The need to consult widely on the models underlying the analyses was noted and it was agreed that an effective way of achieving this was to involve a number of people with relevant expertise. It was agreed that further work on risk analyses conducted on behalf of SEAC should be guided by a group of experts. The main objectives of setting up a risk assessment model were to estimate the impact of measures which might be taken to reduce the risk from any possible exposure and also to enable rapid evaluation of the effects of new information.

In the second session the meeting noted the uncertainty about a number of key biological factors which might be better understood following further research. These included the relative sensitivity of different species to infection with the BSE agent and the roles of the genetics, immune system and gut physiology of the host species in the pathogenesis of the disease. It was noted that there was not yet enough evidence to determine whether there was a threshold level of infectivity required to establish infection in animals or whether an infectious dose could be accumulated.

In session 3 the meeting reviewed the possible routes of human exposure to BSE for the purpose of risk assessment and against which to judge the effect of the measures in place. In session 4 the meeting reviewed BSE infectivity in tissues. It was noted that detection of infectivity was dependent upon the sensitivity of the bioassay which would be affected by the species barrier factor when a different species was used as recipients. Note was also made of the progress of bioassays of infectivity in tissues from cattle exposed to BSE, using cattle as recipients, where there would be no species barrier. The Committee considered this work was essential but recognised it would take many years to complete due to the long incubation periods involved.

In the final session the participants reviewed the effects of legislation on the control of the epidemic in cattle and protection of public health, noting that the two were closely linked. Without the early legislation (the ruminant feed ban of 1988 and the specified bovine offals ban of 1989 for human food and 1990 for animal feed) the number of cases of BSE in cattle would have continued to rise exponentially. The over thirty month scheme was also noted to have had a major impact in protecting the public from exposure to cattle infected with BSE; more than ninety percent of the animals slaughtered in the last year of incubation before onset of clinical disease were estimated to be removed from the food chain by this measure.

Following the workshop SEAC reviewed aspects of the possible risk of infectivity in milk, including milk processing procedures, the latest scientific evidence and proposals for further research. The discussions were informed by industry experts and scientists with expertise in the field. The Committee concluded that there was no reason to change their previous advice on the safety of milk.

The Committee also noted recent research claiming to show that it was possible for rodents to retain experimental TSE infectivity without exhibiting signs of disease within their life-span. The Committee approved the research proposed to examine whether sub-clinical infection could be detected in cattle.

SEAC
May 1998