- Scientists have warned that BSE may have been present
in about 1,500 British sheep at the height of the disease in cattle in
the early 1990s and may still be present in about 20 animals.
- Scientists say that, if sheep can transmit BSE between
members of a flock, a large epidemic could develop
- A British team, which includes the head of the Institute
of Animal Health, Prof Chris Bostock, has warned that this outbreak could
build into an epidemic if nothing is done over a long period.
The Food Standards Agency said in the summer there was a theoretical possibility
that sheep were infected with BSE by the same contaminated feed fed to
cattle in the 1980s and early 1990s.
But this is the first time figures have been put on the numbers involved,
which are very small compared with a national flock of about 40 million.
Although the current prevalence of the disease is probably low, the scientists
say that if sheep can transmit BSE "horizontally" between members
of a flock - as is the case with the equivalent sheep disease scrapie -
a large epidemic could eventually develop.
Fewer than 50 flocks would have been exposed to BSE by 2015 and the model
predicts that the maximum number of flocks exposed is just over 21,000,
or about 40 per cent of the national flock after a century.
In the journal Science, Dr Rowland Kao of Oxford University and colleagues
in Oxford and the Institute of Animal Health, Compton and Edinburgh, calculate
the potential size and duration of a BSE epidemic in sheep, based on the
numbers of infected cattle, the dose responses of cattle and sheep to BSE,
their levels of exposure to infected feed, and the number of BSE-susceptible
sheep in the UK.
But Dr Kao said that it was unlikely that there would be a sudden surge
in the probability of eating BSE-infected animals - and therefore no panic
- but that "by no means should we be complacent that the problem would
just go away on its own".
The scientists conclude that the study shows the importance of a current
plan to breed sheep that have an in-built genetic resistance to scrapie.