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The Genetic Hypothesis for BSE
Editorial
Filed 7 Dec 03
© www.land-care.org.uk
Professor Malcolm Ferguson-Smith of the
Department of Clinical Veterinary Medicine, University of Cambridge
has written an interesting and important letter published in this
week’s Veterinary Record (1).
He refers to the number of BSE-affected
cattle that continue to be discovered. Thus in 2002, while the annual
numbers continued to fall, over 1000 affected cattle were identified
by active and passive surveillance in Great Britain.
The real ban on animal protein in animal
feed came into force on August 1st 1996. Since then there has been
an increasing number of BSE cases in cattle born after that date
(Born After Reinforced Ban - BARBs), which now amounts to 59 in
Great Britain (2) and 9 in Northern Ireland. DEFRA
scientists, using epidemiological techniques, have not been able
to identify the route of infection in these BARB animals. DEFRA’s
previous assertion (that always seemed somewhat suspect) that infected
animal feed was still reaching farms now appears to have even less
credibility.
The BSE Inquiry raised the possibility
that BSE originated from a novel germ line mutation in cattle in
the south of England, and that this initiated an epidemic which
was spread by meat and bone meal in cattle feed contaminated by
the infective prion protein. Professor Ferguson-Smith has logically
pointed out that recent BARB cases may be the direct descendants
of the original animal that started the epidemic over 30 years ago.
This hypothesis could readily be tested
by DNA sequencing. The bovine prion gene is only 851 base pairs
in size and presents no difficulty to molecular biologists who daily
sequence much larger genes of greater complexity. Yet this has not
been done, as admitted at an open meeting of SEAC on November 26,
2003. Why has it not been done?
As Professor Ferguson-Smith points out
in his Veterinary Record letter it has been medical practice to
screen all patients with vCJD for mutations using a technique similar
to that required in cattle. The human gene is almost identical to
the bovine gene. The costs would be modest amounting to a few hundred
pounds. If a germ line mutation was found, a strategy could be developed
to prevent further cases.
BSE was recently diagnosed in a single case
in Canada with massive economic consequences (3).
Likewise in Japan. The origin of these cases is uncertain. In the
Japanese case and in some Italian cases the biochemical characteristics
of the infective prion protein are believed to be different from
UK cases. Such differences could be explained as resulting from
new mutations of the bovine prion protein.
Again looking at the human situation, human
familial CJD is known to be caused by over 40 different germ line
mutations of the prion gene. This is only to be expected as a rare
occurrence in all mammalian species. Sporadic CJD in man is likely
to be due to mutations occurring in tissues other than the germ
line. Indeed, in the words of Professor Ferguson-Smith
“mutation is the only certain origin
of prion disease discovered up to the present time”
In Land-Care’s view why the Spongiform Encephalopathy Advisory
Committee (SEAC) have so far declined to pursue the genetic hypothesis
in relation to the origin of the BSE epidemic in cattle remains
as mysterious as it is unsatisfactory. Could it be that the members
of SEAC are too focussed on projects from which their own researches
are funded?
It won’t be for the first time that
the impartiality of SEAC has been questioned (4,
5).
May we look to SEAC to provide convincing
evidence that their highly expensive activities are based on a level
of scientific integrity that the public has every right to expect?
© www.land-care.org.uk
References
1. Ferguson-Smith, Malcolm A.
(2003). Continuing anxiety about BSE. Veterinary Record, vol 153,
no 23, December 6, p 723.
2. Wilesmith, J. W., Stevenson,
M. A., Morris, R. S., Ryan, J. B. M., Arnold, M. and Prince, M.
(2003). 2003 prepublication: An epidemiological update of cases
of BSE born after 31 July 1996 in Great Britain. See www.seac.gov.uk/papers/seac80_4pdf
3. USDA (2003). Statement by Agricultural
Secretary regarding Canada's announcement of BSE investigation,
May 2003
http://www.usda.gov/news/releases/2003/05/0166.htm
4. Linklater, Magnus (2003).
Government stops funding for BSE critic. Reproduced from THE TIMES
April 24, 2003. www.timesonline.co.uk
See TSE Homepage, Filed 25 April 03, www/land-care.org.uk Click
Here to View
5. Wilson, C., Hughes, L. E.
Rashid, T., Ebringer, A. Bansal, S. (2003).
Antibodies to Acinetobactor Bacteria and Bovine Brain Peptides,
measured in Bovine Spongiform Encephalopathy (BSE) in an attempt
to develop an antemortem test.
J. Clin. Lab. Immunol. (2003). Published on line 13 March 2003 (Click
here to view, pdf)
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