Canada's leading expert on transmissible spongiform encephalopathies says the unsettling hypothesis presented this week in The Lancet might be accurate. "All I can say at this point is it's plausible. It's not out to lunch," Dr. Neil Cashman said from Vancouver, where he teaches in the department of neurology at the University of British Columbia. "But it's also not clear whether this hypothesis is true, or even if this hypothesis can be tested."

It had previously been thought the brain-wasting disease passed to cattle through remains of sheep infected with scrapie (the sheep equivalent of BSE) that were added to cattle feed. The theory continued 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 team suggests 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, known as BSE or mad-cow disease. The remains of the animals would have been rendered and mixed into new batches of feed, infecting more animals. Eventually, a new version of the disease, vCJD, passed back into humans.

Authors Alan and Nancy Colchester admit that their hypothesis is based on circumstantial evidence. "We do not claim that our theory is proved, but it unquestionably warrants further investigation," they wrote. The pair notes that hundreds of thousands of tonnes of mammalian remains were imported to Britain for use in fertilizer and animal feed during the 1960s and '70s. Nearly 50-per-cent was from countries of the Indian subcontinent.

"In India and Pakistan, gathering large bones and carcasses from the land and from rivers has long been an important local trade for peasants," the Colchesters say in their article. "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. Because of the cost of a full cremation, many corpses are partially burned, then deposited in a 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 the infectious prions (misformed proteins) that cause transmissible spongiform encephalopathies. (A Canadian government spokesman said there is no evidence animal products containing human remains would have found their way here.)

Two neurologists from India's National Institute of Mental Health and Neurosciences in Bangalore challenged the controversial hypothesis in a commentary that accompanies the article, arguing that it is not clear that putrefied human remains would remain infectious.

Susarla Shankar and P. Satishchandra also argue 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 warn. "Facts to support or refute their hypothesis now need to be gathered with urgency and great care."