WASHINGTON — Scientists said Sunday that they have used genetic engineering techniques to produce the first cattle that may be biologically incapable of getting mad cow disease. The animals, which lack a gene that is crucial to the disease’s progression, were not designed for use as food. They were created so that human pharmaceuticals can be made in their blood without the danger that those products might get contaminated with the infectious agent that causes mad cow. That agent, a protein known as a prion, can cause a fatal human ailment, Creutzfeldt-Jakob disease, if it gets into the body. More generally, scientists said, the animals will facilitate studies of prions, which are among the strangest of all known infectious agents because they do not contain any genetic material. Prions also cause scrapie in sheep and fatal wasting diseases in elk and minks. In the future, experts said, similar techniques might be used to engineer animals with more nutritious meats - though the Food and Drug Administration has said it will require engineered food animals to pass tests far more stringent than those it recently deemed adequate for clones. ‘This is a seminal research paper,’ […]