A new and disturbing theory about the possible origin of "mad cow" disease has been published, and a Canadian scientist said it is "plausible."
In a report in the British medical journal, The Lancet, Professor Alan Colchester of the University of Kent in England says BSE (bovine spongiform encephalopathy) may have been caused by the tonnes of animal bones and other tissue imported in the '60s and '70s from India for animal feed which also may have contained the remains of humans infected with Creutzfeldt-Jakob disease (CJD).
Colchester, and his daughter Nancy, from the college of medicine and veterinary medicine at the University of Edinburgh in Scotland, said the practice may still be taking place elsewhere. They said it is important to discover whether other countries are importing animal byproducts contaminated with human remains that are destined for feed mills.
The authors admitted their hypothesis is based on a compilation of circumstantial evidence. They wrote: "We do not claim that our theory is proved, but it unquestionably warrants further investigation."
It had previously been thought that the brain-wasting mad cow disease passed to cattle through remains of sheep infected with scrapie -- the sheep equivalent of BSE -- that were added to cattle feed.
The once widely held theory was that humans who ate infected beef developed a human form of BSE. It became known as variant Creutzfeldt-Jakob disease or vCJD, to differentiate it from the classic human forms of the disease, which can occur sporadically or run in families.
But the British authors have suggested a reverse scenario: the remains of humans infected with classic CJD were fed to cattle, which became ill with a bovine version of the human disease. The remains of those cattle would have been rendered and mixed into new batches of feed, infecting more animals. Eventually a new version of the disease passed back into humans and was dubbed vCJD.
The first case of BSE was identified in 1986 in Britain. The first human case of vCJD was diagnosed in 1995, also in that country. Britain has borne the brunt of the vCJD epidemic, with more than 150 human cases.
The Colchesters disputed the scrapie theory by noting that scrapie prions -- the highly infectious misfolded proteins that cause transmissible spongiform encephalopathies -- would have been in the cattle feed chain for decades before BSE arose.
Scrapie has been endemic in Britain for more than 200 years and sheep remains have been fed to cattle there for at least 70 years.
As well, cattle which are experimentally infected with scrapie develop a disease, but it is markedly distinct from BSE.
The Colchesters noted that hundreds of thousands of tonnes of mammalian remains -- whole and crushed bones and carcass parts -- were imported to Britain for use in fertilizer and animal feed during the 1960s and '70s. Nearly 50 per cent was from the countries of the Indian subcontinent.
They wrote: "In India and Pakistan, gathering large bones and carcasses from the land and from rivers has long been an important local trade for peasants. Collectors encounter considerable quantities of human as well as animal remains as a result of religious customs."
Hindu doctrine instructs that bodies should be cremated and the remains deposited in a river, preferably the legendary Ganges. But because of the cost of a full cremation, many corpses are partially burned, then deposited in a river.
Canada's leading expert on transmissible spongiform encephalopathies -- as mad cow and its sister diseases are called -- says the unsettling hypothesis may be accurate.
"All I can say at this point is it's plausible. It's not out to lunch," Dr. Neil Cashman said Thursday from Vancouver.
Cashman -- who teaches in the department of neurology at the University of British Columbia -- agreed that many authorities have retreated from the scrapie theory.
He said: "It stands to reason that somebody scavenging material -- animal material -- from the Ganges or the banks of the Ganges occasionally, accidentally or deliberately, would include human remains in their collections. In general, they're animal carcasses. But human remains find their way into these rendering batches."
He believes the authors are justified in their concern that the practice of using human remains in animal feed may be ongoing.
The report authors noted that in 2004 a group of volunteers working to reduce pollution in the Ganges retrieved 60 human corpses from its waters in two days over a 10-kilometre stretch of the river.
Based on standard rates of CJD infection the authors speculate that a portion of the human remains that made their way into animal feed in Britain would have contained prion-laden tissue.
Cashman said: "This is also not crazy. It's also plausible."
A Canadian government spokesperson said there is no evidence animal byproducts containing human remains would have found their way to this country.
"We know that we never imported bovine material -- meat and bone meal -- from that part of the world," said Alain Charette, media relations officer with the Canadian Food Inspection Agency. "We don't have trade channels open with them because of the animal diseases they have. The only country we trade with on meat and bone meal is the United States."
Two neurologists from India's National Institute of Mental Health and Neurosciences in Bangalore challenged the hypothesis in a commentary which accompanied the article, arguing that it's not clear that prions would retain their infectivity in putrified human remains.
Susarla Shankar and P. Satishchandra also argued that any infectious material would have been heavily diluted, first by the other remains, then by the other ingredients of the animal feed.
"Scientists must proceed cautiously when hypothesizing about a disease that has such wide geographic, cultural and religious implications," they warned.
"Facts to support or refute their hypothesis now need to be gathered with urgency and great care."
But Cashman of UBC wondered if there was any way to prove or disprove the theory, noting it might require feeding infected human brain material to cattle -- an experiment the public might not tolerate.
He said: "That is the experiment from hell. Can you imagine what kind of public response there would be if you or I started an experiment where we were feeding human brains to cattle? It's like Frankenstein."