The Prion Puzzle
ZURICH – The outbreak of mad cow disease in the United Kingdom, which ultimately led to the slaughter of 3.7 million cows and severely damaged the British cattle industry, began insidiously. In 1986, a UK cow developed an unknown brain disease. The following year, tests revealed that the brain had been eroded by a myriad of small vacuoles, producing the sponge-like appearance that inspired the disease’s scientific name: bovine spongiform encephalopathy. Within a few months, cases began appearing throughout the country.
A similar disease, called scrapie, was common in sheep, but had not previously been diagnosed in cows. And a nearly identical, invariably lethal disease, kuru, had ravaged the aboriginal people in Papua New Guinea throughout the twentieth century. Both kuru and scrapie are infectious.
Kuru was transmitted through cannibalistic rituals that were commonplace in Papua New Guinea until the 1950’s. Similarly, in the UK and elsewhere, healthy cattle were fed meat and bone meal made from infected cattle. The resulting epizootic (animal epidemic) affected more than 280,000 cows. At its peak in 1992, mad cow disease was claiming nearly 1,000 head of cattle weekly.