Plastic cup in hand, Linda A. Detwiler is ready to begin. "Hold its nose, and usually it urinates," she explains of sheep. The flock's burly owner, Dick Sisco, tucks the head of a recalcitrant 200-pound lamb under one arm and clasps its muzzle with both hands. Almost immediately, the translucent sample container fills about a quarter of the way. "I didn't think it was going to be that easy," Detwiler remarks. As senior staff veterinarian for the U.S. Department of Agriculture's Animal and Plant Health Inspection Service (APHIS), the 44-year-old Detwiler is collecting urine from certified healthy sheep on a New Jersey farm. The request comes from researchers hoping to create a urine test that can detect the presence of an invariably fatal neurodegenerative disease. In sheep it's called scrapie, because some afflicted ovine scrape themselves raw. In cows it's bovine spongiform encephalopathy (BSE)--mad cow disease.

Besides roiling economies, BSE threatens human health (unlike foot-and-mouth disease, with which BSE is often confused). It has already doomed about 120 people, in the guise of the brain-wasting variant Creutzfeldt-Jakob disease. The cause seems to be a misfolded prion protein that triggers normal prions in the body to adopt the pathogenic conformation. The U.S. announced its first case in April, a 22-year-old Florida woman who had probably contracted the illness during her U.K. childhood.

This article was originally published with the title Keeping the Mad Cows at Bay.

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