By Paul Rincon
BBC News science reporter
The first cases of BSE or "mad cow disease" could have been caused by animal feed contaminated with human remains, says a controversial theory.
The origins of BSE remain murky
Some raw materials for fertiliser and feed imported from South Asia in the 60s and 70s contained human bones and soft tissue, the Lancet reports.
Bone collectors could have picked up the remains of corpses deposited in the Ganges river to sell for export.
If infected with prion diseases, they could have been the source for BSE.
But the theory has been greeted with scepticism by several experts on Bovine Spongiform Encephalopathy (BSE).
The authors admit their evidence stops short of proving their case, but argue that their theory is plausible enough to warrant further investigation.
The appearance of a form of CJD in humans, known as variant CJD or vCJD, has been linked to the BSE outbreak and is blamed for hundreds of deaths.
Prions, the abnormal proteins that cause CJD and vCJD in humans, BSE in cows and scrapie in sheep, are remarkably resistant to both natural decay and sterilisation procedures.
The UK imported hundreds of thousands of tonnes of whole bones, crushed bones and carcass parts in the 1960s and 1970s to make fertiliser as well as meat and bone meal feed.
Nearly 50% came from Bangladesh, India and Pakistan, where gathering large bones and carcasses from the countryside and from rivers is an established local trade.
Hindu funerary practices require that human remains are disposed of in a river, preferably the Ganges. Although the body should ideally be burned, many people cannot afford enough wood for a full cremation, the report's authors claim.
Simply smoking the pelvis in women and the torso in men is sometimes enough. And many complete corpses are thrown into the Ganges.
The Ganges occupies an important place in Hindu religious life
"There are a whole range of public health concerns over Ganges pollution," lead author Professor Alan Colchester, of the University of Kent, told the BBC News website.
"But amongst all the recognition of potential problems, I don't think anyone has thought about the very rare but very important risk posed by the corpse of someone who has died from a version of CJD."
Human remains have been described in material delivered to processing mills. And during the 1960s, human material was confirmed in consignments of bones shipped into French docks from Asia.
A spokesman for the Department for Environment Food and Rural Affairs (Defra) said it went along with the findings of a 2001 report into the origin of BSE, where a favoured hypothesis was that BSE had its origins with scrapie.
But the spokesman said the department was open minded about new findings.
Dr David Brown of the University of Bath, an expert in prion diseases, told the BBC News website: "It's certainly a possibility that you can't rule out completely, but I would say that on a scale of probability, it would be down at the low end."
Professor Colchester estimates that about 120 Hindu people die from CJD each year. But Dr Brown pointed out that the poor, who might account for many corpses in the Ganges, also have a relatively short life expectancy. Human prion diseases, meanwhile, often present themselves in old age.
Professor Susarla Shankar, head of neurology at the National Institute of Mental Health and Neurosciences in Bangalore, India, said he thought the theory would not stand up to scientific scrutiny.
"If this was so, you would expect to find more cases of BSE in Indian cattle. At the moment, the surveillance centre doesn't have a single case," he told the BBC News website.
Bone collecting was a traditional practice, he said, but added that even if some human material was making it into the raw materials for animal feed it would be so little as to be of scant consequence.
But only a tiny amount of contaminated brain tissue is needed to transmit human CJD to nonhuman primates in the lab. On the other hand, nothing is known about the transmission of human prion diseases to cattle.
It was shown in the 1980s that prion proteins could survive the entire chain of processes leading to the production of animal feed in an infectious form.
The feeding of mammalian meat and bone meal to farm animals has been banned since 1996. Yet sporadic cases of BSE have occurred in the UK and in Europe, where regulations were also tightened, since the ban. These cases remain unexplained.
Professor Bill Hill of the University of Edinburgh said the incidence of the disease is falling and that it was hoped BSE could be eradicated altogether by adhering to measures put in place to control the disease.