March 23, 2007

Research downplays scrapie theory as cause of BSE 
 

The leading theory that bovine spongiform encephalopathy or BSE has come from feed containing sheep material infected with scrapie has been renounced by European researchers, reports the British journal New Scientist. 

The 200-year presence of scrapie--a fatal, degenerative disease that affects the nervous systems of goats and sheep--in UK sheep flock which have been pointed as the culprit for BSE emergence in British cattle in the 1980s has nothing to do with the dreaded cattle disease. 

This was evidenced by an experiment where cows given scrapie-laden feed has tested negative with BSE. The study also revealed many countries have included sheep remains in cattle feed without creating BSE.

The study has led some scientists to speculate that BSE occurred as a rare spontaneous condition in cattle, which spread to other cows when they ate these animals' remains.

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

If BASE can mutate into BSE, this could well be how BSE emerged, according to Tagliavini Tagliavini from the Carlo Besta Neurological Institute in Milan.

BASE turned into BSE after cattle remains were fed to sheep is another possibility, said to Hubert Laude of the French national agricultural research INRA. In his preliminary research, Laude attested that he got BASE to turn into BSE in mice engineered to carry sheep prion protein (PrP), but not in mice with cow or human PrP. This would suggest that sheep could have acquired BSE from cattle infected with BASE. Cattle would then have got BSE by being fed with BSE-infected sheep material.

BASE has not been discovered in British cattle yet.

BSE still plagued British cattle herds in 2006 despite the government's reinforced feed ban (BARB) in 1996. Although the numbers of affected cattle have fallen since its peak in 2003, around 160 cases have been detected since and proportionally similar numbers have been found in other EU countries.

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. In this case, British scientists believe that very small amounts of the infectious agent could cause BSE and the tail of the epidemic could still remain for a number of years.