Volume 3: The Early Years, 1986-88
3. Epidemiology
MBM the likely factor

3.52 The rendering process produces MBM and tallow. Mr Wilesmith was concerned to discover the relative risks of tallow and MBM which contained the scrapie agent. On 5 April 1988 he wrote to Dr Hope at the NPU seeking his advice on this point and enclosing the reports that had been prepared by Mr Peter Smith in relation to the rendering processes. ¹

3.53 Dr Hope replied on 27 April expressing the view that no guarantee could be made that scrapie infectivity was absent from any grade of waste. He suggested that laboratory experiments could provide guidance on the relative risks of tallow and MBM containing BSE/scrapie infectivity. ² Mr Wilesmith subsequently discussed this matter with Dr Kimberlin, who had just left the NPU to set up as a private consultant. Dr Kimberlin expressed the view that scrapie-like agents would be more likely to partition with the MBM fraction because of their 'membrane adherence' properties. ³

3.54 On 26 April Mr Meldrum asked Mr Wilesmith to produce a report within the next two days to enable Tolworth to prepare a final paper for submission to Whitehall. He added: 'I apologise for the rush but we do need to come to some firm conclusions by the end of this week.' ⁴ Mr Wilesmith replied the following day, saying that he could not meet this deadline, and summarising the state of play as follows:

In brief we have no conclusions to explain why BSE should have occurred from the findings of the various investigations on the feedstuffs industry thus far. ⁵

3.55 He went on to explain that investigations were in hand aimed at collecting data from compounders on sources of ingredients. In the circumstances he could only produce a progress report for Whitehall. ⁶

3.56 Mr Wilesmith told us:

In the course of May 1988 I received information which had been requested from feed suppliers on the composition of rations. This information indicated that all affected animals had consumed feed containing MBM. I reported this to Mr Rees, the CVO. This accumulated evidence of MBM as the vehicle of infection was considered sufficient by Mr Rees to submit an appropriate Ministerial submission on 6 May, 1988. ⁷

3.57 On 3 May 1988 Mr Wilesmith produced the report. This summarised the epidemiological investigations that had been completed and were in progress and suggested possible actions for control of BSE. Mr Wilesmith advised:

The epidemiological picture is typical of an extended common source epidemic in which the incidence increases sharply over a short period of time and then maintains at a constant incidence. ⁸

3.58 He went on to explain how histopathological findings, together with the detection of SAFs by electron-microscopy, supported the hypothesis that BSE was a transmissible spongiform encephalopathy (TSE). He added that the theory that BSE might be due to infection with a scrapie agent of sheep and goats was supported by the findings that SAFs in BSE cases had amino acid sequences identical to those of SAFs found in sheep infected by scrapie. Mr Wilesmith then stated his conclusion that the absence of any direct evidence from the epidemiological investigation of other sources of such an agent, coupled with the fact that BSE was a common source epidemic, suggested the introduction of an infectious agent via commercial cattle feedstuffs. He added that no one feed compounder was common to all affected farms. ⁹

3.59 Mr Wilesmith set out the findings reported by Mr Peter Smith (see paragraphs 3.44-3.47). He explained that enquiries of feed compounders were in hand in an attempt to identify the source of MBM and tallow used in the feedstuffs of some 40 affected herds. He added that it was the present opinion of experts on the scrapie agent that MBM was more likely to be the vehicle of the agent than tallow. ¹⁰

3.60 By way of possible action to control BSE, Mr Wilesmith recommended a temporary ban on the inclusion of MBM in cattle and sheep feedstuffs, and added:

It would be helpful in investigating this disease if this ban were made public; epidemiological studies (case control study) could proceed more rapidly. ¹¹

3.61 This comment reflected the fact that so far discussions with UKRA, GAFTA and UKASTA had been on a confidential basis, and that their members (other than those involved in the discussions) had not been informed of the fact that animal feed was the prime BSE suspect.

3.62 Mr Wilesmith's report, added to other information which had been assembled, gave Mr Rees a solid basis for putting forward proposals for action. On 6 May he sent a submission to the Minister which had been agreed with Mr Cruickshank. This submission stated:

The Chief Veterinary Officer is satisfied from the information produced by the investigating teams that the source of the transmissible agent which has caused BSE is through meat and bone meal derived from sheep material in which the rendering process has failed to inactivate the scrapie agent. Affected sheep material is continuing to be processed and it must be assumed therefore that cattle continue to be exposed to infection. ¹²