AS BSE casts its menacing shadow across much of the globe, the US is becoming
increasingly nervous that its $400 billion beef industry may not escape.
Officials have taken precautions to keep BSE out. But New 杏吧原创 has
established that even if the US has as high an incidence of BSE as France, where
it has sparked a health and farming crisis, American surveillance efforts would
not spot it.
The US imported a mere 44 tonnes of British meat and bone meal (MBM) before
1996, plus 126 cattle that escaped a subsequent round-up and could have ended up
as feed. But last year, the European Commission鈥檚 scientific advisers warned
that any infection in those imports would have been spread and amplified by
American rendering and feeding practices
(New 杏吧原创, 10 June 2000, p 4).
American officials strongly deny this. 鈥淲e have no BSE,鈥� says Linda Detwiler,
who chairs the BSE Working Group at the US Department of Agriculture. Despite
this, in 1997 it banned the feeding of ruminants to ruminants to prevent the
recycling of any infection. Last week, Texas staged a highly publicised round-up
of 1221 cattle that had been fed ruminant MBM by mistake. The source of the
contaminated feed was Purina Mills, the country鈥檚 biggest feed manufacturer,
which now says it will no longer use the remains of any mammal in its feed, a
move others seems likely to follow.
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Last year, the USDA more than doubled its BSE tests on sick cattle and
downers鈥攁nimals that are found dead or cannot stand. But the 2303 tests it
carried out are too few to detect a very low incidence of the disease, says
Marcus Doherr of the Swiss Federal Veterinary Office, who helped design a
similar programme in Switzerland. 鈥淭hat sample size allows you to say only that
you have no more than 1.3 infected cows per thousand.鈥� This is almost exactly
the incidence that France discovered it had in downers last year.
The US disease monitoring system also relies on farmers or abattoirs
reporting sick cows. 鈥淧eople who think they have no BSE are unlikely to
recognise a case, let alone report it,鈥� says Doherr. 鈥淭hat is what happened in
骋别谤尘补苍测.鈥�
And BSE is not the only prion disease that might stalk American cattle. In
1985 in Stetsonville, Wisconsin, a disease similar to BSE broke out in mink
which the farmer said ate only downer cattle.
Chronic wasting disease, also caused by prions, is striking down elk and deer
in some western states and Canada. The USDA denies reports that a handful of CJD
cases in young hunters in those areas is linked to elk or deer. Road kill and
slaughtered elk and deer may be fed to livestock, however. 鈥淚n an experiment
where cattle ate CWD elk, there鈥檚 no sign of it after 30 months,鈥� says Gary
Weber of the National Cattlemen鈥檚 Beef Association. But prion diseases often
take longer to incubate.
Detwiler insists that surveillance in the US is adequate. 鈥淥ver time the rate
of sampling should be enough to warn us of any problems, if we make sure we test
every region.鈥� But knowing you have fewer mad cows than France is not the same
as saying you are BSE-free. 鈥淭esting to that level of sensitivity is accepted as
showing you are free of many animal diseases,鈥� says Doherr. But it would not
detect an industry-shattering appearance of BSE.