杏吧原创

A SURVEY of British farmers suggests it鈥檚 unlikely sheep became widely
infected with BSE when the disease was raging in British cattle.

If you feed meat and bone meal (MBM) from cattle with BSE to sheep as an
experiment, they develop symptoms similar to scrapie, a common prion disease in
sheep that is not thought to spread to humans. This led to fears that BSE was
spreading unnoticed in sheep during the late 1980s and early 1990s, when the
disease was rife in British cattle, and sheep ate bovine MBM.

If sheep had become widely infected, people might have eaten BSE-infected
mutton and lamb, and the infection might have persisted unnoticed in flocks
(New 杏吧原创, 4 November 2000, p 8).
But if this was so, cases of 鈥渟crapie鈥� should have surged in the early 1990s.

So Mike Gravenor and colleagues at the Institute for Animal Health in
Compton, Berkshire, sent 11,000 British sheep farmers an anonymous
questionnaire. Their answers show that the chances of a farm鈥檚 flock getting
scrapie doubled gradually over the 20 years from 1970 to 1990. But no surge
coincided with the epidemic of BSE.

鈥淭his rules out a large-scale increase,鈥� says Gravenor. 鈥淧erhaps sheep are
less susceptible to infection in the field. Or perhaps they weren鈥檛 fed much
MBM.鈥� The gradual rise in scrapie cases may have been due to improved diagnosis
and larger flock sizes. But, he cautions, the data is not sensitive enough to
rule out BSE in some flocks. It also reveals that farmers only reported 209 of
the 1600 cases of scrapie that probably occurred in 1998.