A veterinary scientist has proposed a new theory for the origin of mad cow disease1, saying he believes it likely came from a wild animal commonly found outside Britain that was chopped up2 for cattle3 feed in England.
   Roger Morris, a professor of animal health at Massey University in New Zealand, has spent years investigating about a half-dozen credible theories of how British dairy cattle4 could have contracted the disease, blamed5 for the deaths of 81 people so far.
   Until now, scrapie6, a brain-wasting7 disease found in sheep, has been the prime suspect because of its similarities to bovine spongiform encephalopathy, or BSE. But Morris said his research indicates it is less likely the outbreak8 was caused by cows being fed scrapie-infected sheep.
   Morris said he is investigating a list of about 15 suspected wild animals, but would not specify them until his research is published in a scientific research journal sometime next year.
   "There are a range of wildlife species I see as potential sources, but I've not yet come to a conclusion on which species it's most likely to be," he said in an interview this week.
   Dr. Hugh Pennington of Aberdeen University in Scotland, who has researched the disease, said Morris' theory was just one of a number of credible theories of the origins of the outbreak. Pesticides and bacteria have been ruled out9 as the cause.
   Experts say that while pinpointing the origins of mad cow will not help the British control the human form of the illness, variant Creutzfeld Jacob disease, it is important for heading off10 future outbreaks elsewhere around the world.
   An independent committee commissioned11 by the British government published a report Thursday that also downgraded12 the idea that mad cow disease originated from scrapie. But that group reached a different conclusion, which has been questioned by some experts - that a genetic mutation in a single cow was responsible.
   "I rank13 that low. The genetic mutation theory is even less likely than scrapie. There's no evidence for it at all," Morris said.
   Morris said he theorizes14 that a wild animal carrying a version of BSE specific to its own species somehow arrived in Britain, was captured and its brain and organs ended up in a batch15 of feed given to about 1,000 dairy cows in the southwest of England between 1975 and 1977.
   About half of the cows then became infected, he said, adding that the infected cattle ended up16 in other parts of the country, before being recycled as cattle feed in 1981, spreading the disease.
   BSE has an incubation period of about five years. The first cases of mad cow disease were identified in Britain in 1986. Scientists believe humans caught the disease17 by eating processed food containing the infected brains and organs.
   Scrapie, BSE and variant Creutzfeld Jacob disease are all types of illnesses known as transmissible spongiform encephalopathies. They are all fatal and result in a mass of sponge-like18 holes in the brain.
   Scrapie was the only other similar disease known to infect farm animals and waste19 from slaughtered20 sheep was used in cattle feed, so scientists focused on investigating a link between the two diseases.

The Independent.com