Mad cow linked to humans

2005-09-02 10:20

London - A new theory proposes that mad cow disease may have come from feeding British cattle with meal contaminated with human remains infected with a permutation of the disease.

The hypothesis, outlined in The Lancet medical journal, suggests that the infected cattle feed came from the Indian subcontinent, where bodies sometimes are thrown into the Ganges river.

Indian experts not connected with the research exposed weaknesses in the theory, but agreed it should be investigated.

The cause of the original case or cases of mad cow disease, or bovine spongiform encephalopathy, is unknown.

It belongs to a class of illnesses called transmissible spongiform encephalopathies, or TSEs. They exist in several species. Scrapie is a TSE that affects sheep and goats, while chronic wasting disease is one that afflicts elk and deer. A handful of TSEs are found in humans, including Kuru, Alper's disease and Creutzfeldt-Jakob disease, or CJD.

All the TSEs are fatal, untreatable and undiagnosable until after death. They are called spongiform encephalopathies because the diseases involve spongy degeneration of the brain.

The disease was not known to infect cows until 1986, when the first cases were noticed in Britain. About a decade later, a new permutation of CJD, which scientists dubbed variant CJD, started showing up in people there. Experts believe this new variant comes from eating beef products infected with mad cow disease.

A mystery

But where the cows got their disease in the first place remains a mystery. The most popular theory is that cattle, which are vegetarian, were fed meal containing sheep remains, passing scrapie from sheep to cows, where it eventually evolved to become a cow-specific disease. Another theory is that cows just developed the disease spontaneously, without catching it from another species.

However, British scientists now propose the origin may be the bones of people infected with classical CJD, which they theorise ended up in cattle feed imported from South Asia.

Britain imported hundreds of thousands of tons of whole bones, crushed bones and carcass parts to be used for fertiliser and animal feed during the 1960s and 1970s. Nearly half of that came from Bangladesh, India and Pakistan, said the scientists.

"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 scientists wrote. "Collectors encounter considerable quantities of human as well as animal remains as a result of religious customs."

Britain was the main recipient of animal byproducts exported from India and Pakistan during the relevant period and was also a leader in feeding meat and bonemeal to calves, they noted.

Finally, the similarities between the strains - mad cow disease, classical CJD and variant CJD - are sufficiently close to support the theory of a link among them, the authors argue.

- AP