News last update:6 Aug 2012

Scrapie may not be the cause of BSE

European researchers have found evidence which could suggest that the emergence of BSE in British cattle in the 1980s had nothing to do with the 200-year presence of scrapie in the national sheep flock, the New Scientist reports.

The leading theory on the emergence of BSE has been that cattle initially contracted the disease by eating feed containing sheep material that was infected with scrapie. However, attempts to duplicate this process by giving scrapie to cows in laboratory conditions have failed. In addition, many countries have included sheep remains in cattle feed without creating BSE. This has led some scientists to speculate that BSE arose as a rare spontaneous condition in cattle, which spread to other cows when they ate these animals' remains.

This theory appears to have been strengthened by Italian research into the rare cattle prion disease bovine amyloidotic spongiform encephalopathy, or BASE, which affects older animals and is distinct from BSE.

BASE mutates into BSE
If BASE can mutate into BSE, this could well be how BSE emerged. "I think BASE is a natural prion disease of older cattle, which turned into BSE," says Tagliavini Tagliavini from the Carlo Besta Neurological Institute in Milan.
Another possibility is that BASE turned into BSE after cattle remains were fed to sheep. In preliminary research, Hubert Laude of the French national agricultural research agency INRA, says that he got BASE to turn into BSE in mice engineered to carry sheep PrP, but not in mice with cow or human PrP. This would suggest that sheep could have got BSE from cattle infected with BASE. Cattle would then have got BSE by being fed with BSE-infected sheep material.

Contaminated feed
New cases of BSE in UK cattle born after the reinforced feed ban in 1996 (BARB cases) continued to appear in 2006, although numbers have fallen since the peak in 2003. To date 160 BARB cases have been detected and proportionally similar numbers have been found in other EU countries. BASE has not been discovered in British cattle yet. The BARB cases are thought to be the result of very low level contamination of feed that is either imported or comes from feed bins on farms containing residual amounts of old feed. If this is the case, then very small amounts of the infectious agent could cause BSE, and the tail of the epidemic could continue for a number of years.

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