Volume 3: The Early Years, 1986-88
3. Epidemiology
Initial investigations and conclusions

3.3 In May 1987 the CVL had a small Epidemiology Department headed by Mr John Wilesmith. ¹ Mr Wilesmith was the only qualified epidemiologist at the CVL, having taken, after his veterinary training, a postgraduate degree in medical statistics and epidemiology at the London School of Hygiene and Tropical Medicine. His department consisted of two veterinary research officers (VROs), a mathematician/statistician, a systems analyst, five scientific officers skilled in computer programming, and five clerical staff. The department conducted research on diseases of national, economic and public health importance and on novel diseases of animals.

3.4 Mr Wilesmith knew nothing of BSE until Dr Watson, the Director of the CVL, visited his office in late May 1987 and told him about the newly identified disease in cattle. Dr Watson asked him to investigate its epidemiology. ²

3.5 On 3 June 1987 Mr Wells gave Mr Wilesmith a more detailed briefing. This included a description of the clinical symptoms and the basic histological features of the disease. He told Mr Wilesmith that histopathological examination had confirmed six cases on four farms in three different areas, and that clinical histories suggested that there had been earlier cases in 1985. The possibility that the disease was similar to scrapie was discussed and Mr Wells said it was possible that the cases had a toxicological cause. ³

3.6 Mr Wilesmith designed a questionnaire for use on farm visits with the object of eliciting, in the case of each casualty, any information that might have a bearing on the cause of the disease. This included exposure of individual diseased animals to various possible sources of infection such as feed, vaccines and other disease prevention methods, herbicides and pesticides, and contact with sheep. The pedigree of each animal was explored in order to see whether the disease might have a genetic source. ⁴

3.7 A week later, on 9 and 10 June, Mr Wells held discussions with Dr Kimberlin of the NPU in Edinburgh about a future research programme for BSE. Dr Kimberlin gave advice on epidemiology, recommending investigations into herd structure, age and management practices and the influence of these on the recognition of clinical signs; a common use of bulls; connections with sheep; common denominators of a nutritional, infectious or genetic nature; and, in particular, sources of animal protein in feedstuffs. Mr Wells passed this advice on to Mr Wilesmith. ⁵

3.8 When Mr Wilesmith gave evidence, he said that Dr Kimberlin's reference to animal protein was probably aimed at the possibility of scrapie having infected cattle feed via the rendering process. ⁶ He added that this was a possibility that they all had in mind at the time, but that he, Mr Wilesmith, was more interested at that point in the possibility of a contaminated vaccine. ⁷

3.9 Armed with the questionnaire, Mr Wilesmith began to visit farms on which confirmed or suspected cases of BSE had been reported. The number of these increased rapidly as the investigation progressed. Mr Wilesmith was looking for some common novel factor to explain the outbreak of the disease. At first this led him to discount the possibility that a component of the feedstuffs was involved in the aetiology. ⁸ The widespread use of organophosphates and synthetic pyrethroids as insecticides appeared to have potentially greater significance. By the end of the year Mr Wilesmith had, however, discounted these for two reasons. Histological examinations conducted by Mr Wells had demonstrated that the pathological changes associated with BSE differed from those induced by toxicity. Perhaps more significantly, no common factor could be identified in terms of the use of vaccines, hormones, organophosphorous fly sprays, synthetic pyrethroid sprays or anthelmintics. ⁹

3.10 On 30 July 1987 Dr Watson noted that Mr Wilesmith was under considerable pressure as he did his best to obtain detailed information from all affected herds by personal visits. On instructions from Mr Rees, Mr Cranwell was seconded from Starcross VIC in Exeter to assist him in making farm visits and recording data. ¹⁰ During August 1987 the Epidemiology Department began to develop a computer database to record and analyse the data. ¹¹

3.11 On 26 August, by which time 15 farms had been visited, Mr Wilesmith recorded that the potential role of feedstuffs in the aetiology was uncertain: 'Lamb meat and bone is evidently used in commercial dairy rations, but this is not a recent introduction.' Other ingredients under consideration were dried cassava, tapioca and maize gluten meal. ¹²

3.12 On 27 August Mr Bradley and Mr Wilesmith made a joint report to Dr Watson which proposed the tentative hypothesis that 'BSE is caused by an unconventional transmissible agent coupled with unknown genetic factors'. They recommended that transmission studies in mice, rats, cattle and possibly mink should be started immediately to test this hypothesis. However, they advised that it would be premature to eliminate other potential causes of the disease. ¹³