Last week (19 July 2001) saw the publication of an independent review of the origin of BSE (Bovine Spongiform Encephalopathy) undertaken by a team of scientists led by Professor Gabriel Horn, Emeritus Professor of Zoology and former Master of Sidney Sussex College, Cambridge.

Last week (19 July 2001) saw the publication of an independent review of the origin of BSE (Bovine Spongiform Encephalopathy) undertaken by a team of scientists led by Professor Gabriel Horn, Emeritus Professor of Zoology and former Master of Sidney Sussex College, Cambridge.

The review was commissioned by the Government following the conclusions of the BSE Inquiry chaired by Lord Phillips. Professor Horn was asked to select a team to look in greater detail at the issue of the origin of BSE. The team was asked to pull together all scientific understanding, including emerging findings, on the subject. In order to ensure genuine independence, Professor Horn was given a free hand to choose the review team which included experts in animal husbandry, epidemiology, transmissable spongiform brain diseases, neurodegenerative illnesses and medical genetics.

The BSE Inquiry, chaired by Lord Phillips, considered that BSE may have passed through several undetected cycles in England during the 1970s and early 1980s before becoming an overt epidemic in the mid 1980s. The Inquiry also considered that the spread of the disease in cattle came about through the, now banned, use of meat and bone meal (MBM) in cattle feed. Professor Horn's Committee agreed with these considerations and noted that MBM had been used in this way in many countries and for many decades of the 20th century. It was therefore puzzling that there had been no previous outbreaks of BSE epidemics. This issue, and the issue of the geographical location of the epidemic were specifically addressed by the Committee.

"We have identified a number of factors none of which would appear to have been sufficient on its own to cause the outbreak of BSE, but which together may have triggered the epidemic," said Professor Horn.

The Committee noted that during the period 1970 to 1988 feed manufacturers in Britain introduced MBM into the rations fed during the first 12 weeks of life to calves in dairy herds, as a cheaper alternative to the traditional calf starter diet which was mainly composed of vegetable protein. This practice was not widely adopted in continental Europe and it was not adopted in the United States. Nor had it been the practice in Britain prior to the 1970s. The practice was followed in Australia from the 1970s onwards, yet no outbreak of BSE had occurred there. However, Australia is free of scrapie, a disease of sheep in which spongiform changes in the brain are found. The Committee observed that, in Britain, MBM would have included scrapie infected material.

During the 1970s many feed mills changed the way of preparing MBM. Under experimental conditions these changes were found to result in a small but clinically significant increase in the degree of infectivity of the MBM. The Committee suggested that feeding this material to very young calves may have triggered the BSE epidemic. The Committee recommended that experiments are conducted to test whether young calves are more sensitive to the infective agent than are adult cattle.

While the precise origins of BSE necessarily remain uncertain there is strong evidence that the infection is carried by a prion protein. This protein is normally present in the body. Under some conditions the shape of the protein is changed and it then becomes pathological. How this change is brought about is the subject of intense scientific investigation. The suggestion that this protein to protein interaction plays a causal role in scrapie was first proposed in 1967 by J.S.Griffith, a Fellow of King's College, Cambridge.

Commenting on the review Margaret Beckett, the Minister for the Environment, Food and Rural Affairs, said:

"This study will doubtless generate much further scientific debate and I shall be interested to hear SEAC's views on the findings when they consider the report in September."

The study is now being considered by the Spongiform Encephalopathy Advisory Committee who will respond to its findings in September 2001.

The BSE epidemic in the UK continues to decline, along predicted lines. The number of BSE cases confirmed during 2000 was 1,311, 42 per cent lower than in 1999. The number of BSE suspects reported this year to date, 598, is 45 per cent lower than in the same period last year.


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