6 months old in human food. Dr. Meldrum wrote that “the action is based on our understanding of
scrapie in sheep.” He concluded his letter as follows:
BSE is, of course, still a very new disease. Our actions have been firmly based on
scientific evidence and advice, but a great deal of research is necessary and is being
undertaken, for example, to determine whether the agent is absent in a variety of
bovine tissues, to study the agent at a molecular level, to develop a diagnostic test,
to determine whether maternal transmission can occur, and to confirm that embryo
transfer carries no risk of transmission of BSE. The results will inevitably take years
to obtain, but will be published when available.
Articles about BSE also appeared in Canadian journals. In September 1989 scientists at the
Ontario Veterinary College in Guelph, Ontario, wrote an article in the Canadian Veterinary
Journal briefly summarizing what was known about BSE. They suggested the imposition of an
import ban on cattle and sheep from the UK, and that “serious consideration should be given by
Agriculture Canada to preventing incorporation of ruminant-derived rendered products into any
animal foods.”
Although not published until 1990, Dr. Kimberlin submitted an article to the Canadian
Journal of Veterinary Research on 5 June 1989, “Transmissible Encephalopathies in Animals”,
which discussed the “prion hypothesis.” This theory, then quite new but now generally accepted,
is that scrapie, BSE, CJD and other transmissible encephalopathies are caused by an abnormal
infectious protein, known as a prion, which is resistant to inactivation processes such as high
temperature, high pressure, and other rendering techniques that ordinarily destroy bacteria and
viruses, and which can replicate itself. TSEs, Dr. Kimberlin noted, have long incubation periods
(often several years) and occur only in the central nervous system. Dr. Kimberlin, who around this
time was succeeded as head of the of Neuropathogenesis Unit in Edinburgh (“NPU”) by Dr. Hope,
wrote that “the transmission of scrapie to cattle (to give BSE) is clearly associated with the
ingestion of contaminated feed.”
Drs. Bulmer and Kellar were both questioned extensively on their state of knowledge of
BSE as of 1990, and of the conclusions in the scientific studies published to that point. They
acknowledged that Canada was aware of the two hypotheses stated by Dr. Wilesmith in his May
1990 article that BSE stemmed from increased exposure of cattle to scrapie from sheep carcasses,
and from increased exposure of cattle to a cattle-adapted scrapie-like agent through rendered cattle
carcasses. Dr. Kellar also acknowledged the concern, known at the time, that due to the long
incubation period animals could be subclinically, or preclinically, infected with BSE and that
infected material could be recycled from cattle.
Dr. Kellar, a veterinary epidemiologist familiar with studying the causes and patterns of
diseases, agreed that epidemiologists must look at all methods of transmission when trying to
prevent entry, or spread, of a disease. He agreed that Agriculture Canada knew of and followed
epidemiological principles, and that in dealing with a disease such as BSE which has a long period
of undetectable subclinical infection, Canada needed to pursue a conservative, precautionary,
approach.
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