IT WAS cows dining on the ground-up remains of other cows that started the
BSE epidemic. But where did the disease actually come from?
For years the mainstream theory was that some of the meat and bonemeal (MBM)
eaten by British cows must have been infected with an unusual form of the sheep
disease scrapie. But this didn鈥檛 explain why BSE hit Britain in the 1980s:
scrapie was common elsewhere and cattle round the world had been eating MBM for
decades, apparently with no ill effects. So when last year鈥檚 BSE inquiry backed
a rival theory suggesting the disease was a freak event, the result of a random
mutation in a cow back in the 1970s, the media lapped it up.
Now, suddenly, scrapie is back in fashion. A government-appointed panel
believes it can at last explain what was unique about Britain in the 1980s.
Looking at the statistics for BSE, Gabriel Horn, the Cambridge neuroscientist
who led the panel, was struck by the fact that dairy cattle were five times as
likely as beef suckler cattle to go down with BSE. Digging deeper, he discovered
that almost uniquely British farmers began adding MBM to the 鈥渟tarter rations鈥�
fed only to dairy calves.
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Until the 1970s, these rations included reconstituted milk, concentrated feed
and hay. Any protein added was from vegetables or fish. But following Australian
experiments in the 1960s showing that calves thrived if MBM was added to the
feed, manufacturers in Britain and Australia began incorporating MBM into
rations. Crucially, other Europeans didn鈥檛. Nor did the Americans, because
soybean protein was so plentiful and cheap.
Horn believes some of these rations could have been infected with an unusual
form of scrapie that caused BSE in the calves that ate the feed. Calves were up
to 30 times more susceptible to BSE than adult cattle.
But the other side isn鈥檛 giving in. 鈥淚鈥檓 not backing down from the view it鈥檚
a novel disease, different from scrapie,鈥� says Malcolm Ferguson-Smith of
Cambridge University, the scientific expert on Phillips鈥檚 inquiry panel.
According to Ferguson-Smith, the only way new BSE-like diseases can emerge is if
there is a mutation in the gene which makes the normal prion protein. If calves
fed sheep remains were the source of BSE, many cases would have emerged
simultaneously across the country, he claims. But the way the disease actually
spread, suggests a single, focal source in the south of England. 鈥淎ll the
biochemistry says it鈥檚 a new strain, and no scrapie strain produces this in
肠补迟迟濒别.鈥�
Well鈥攏o strain scientists know of yet. But that might not be saying
much. 鈥淭he number of scrapie strains examined is pathetic,鈥� says Martin Bobrow,
a genetics expert at the University of Cambridge and a member of the Horn
committee. Thousands of British sheep come down with scrapie every year, but so
far strains from just 29 sheep have been examined to see if they cause BSE.
鈥淭here are many tens of thousands of scrapie infected sheep in the UK, so
there鈥檚 plenty of room for other strains.鈥�
