New Twist In Tale Of BSE's Beginnings
U.K - The discovery that a rare brain disease in cows can mutate into BSE has given new life to the theory that mad cow disease started out in cattle, rather than crossing over from sheep.
21 March 2007
2 minute read
When BSE emerged in British cattle in the mid-1980s, the leading theory was that they had initially contracted the disease by eating feed containing the remains of sheep infected with scrapie. Both BSE and scrapie are caused by infectious prions, misshapen forms of a normal brain protein. Having made this species jump, BSE would have spread as cattle carcasses were processed into animal fodder and fed back to cows.
Yet attempts to duplicate BSE by deliberately giving scrapie to cows have failed, and many countries 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.
The new twist to the story comes from studies of a disease called bovine amyloidotic spongiform encephalopathy, or BASE. It was discovered in 2003, when two Italian cows, out of tens of thousands of European cattle screened for BSE at slaughter, were found to have a prion disease that seemed different from BSE. The BASE prion had a lower molecular weight and one, rather than two, sugars bound to it. The brains of cows with BASE were also damaged in different places from those with BSE, and had dense protein deposits called amyloid that are not seen in BSE. Similar prions have also turned up in France, Germany and Japan
Source: New Scientist
