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Mad Cow, Chronic Wasting, and Other Prion Diseases
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Diagnosing Prions
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One of the most pressing needs in prion disease work is a live test to determine whether a symptomless individual is infected. Currently, the only real test is a brain postmortem, which looks for the presence of the rogue prion proteins. Scientists are trying to develop tests that would find signs of prions in more accessible substances, such as the tonsils, blood, or urine.
A urine test would probably be the simplest--both for humans and for animals--and researchers are actively working to develop such a test. In May 2002, I accompanied Linda Detwiler of the U.S. Department of Agriculture's
Animal and Plant Health Inspection Service to the New Jersey sheep farm of Dick and Virginia Sisco.
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The Siscos maintain a flock free of the prion disease called scrapie, and Detwiler was there to collect urine that would serve as negative controls in experiments to determine whether a urine test for sheep would be possible. She is also there to assess the practicality of collecting sheep urine; if it’s too difficult, then a urine test for livestock would not be pursued.
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The sheep urinate at the slightest provocation. Notice that the concrete ground is wet after we have entered the pen.
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Collecting their urine, however, requires a more systematic approach. A sheep making a donation is led into a fence-post chute, which makes handling easier.
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To make the sheep urinate, Detwiler explains, you have to hold its nose. So Dick Sisco grabs the snout, and soon Detwiler, crouched at the business end, gets a sample container filled halfway.
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The job proves easier than thought, and soon several sample containers are filled.
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Detwiler also needs blood samples for other work. She feels for the jugular vein underneath the woolly coat. Then, with a needle even finer than those used for humans, she sticks the animal. It’s much messier than urine collection--blood drips around the needle onto Detwiler’s gloved hands and protective jumpsuit.
The urine collection goes quite smoothly, and Detwiler was pleased. If researchers can find signs of the rogue prions in urine, then collecting it from sheep will not be a problem.
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