Medicine: Of Sheep & Men

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Scrapie is a disease of the nerves and muscles of sheep, so named because bleating victims rub themselves against fence posts or wire to relieve the itching that goes with it, and in doing so scrape off valuable wool. In later stages the animals get the shakes and staggers, so the French call the disease la tremblante. Last week veterinary researchers were engaged in a transatlantic argument over whether scrapie is hereditary or infectious, or—as would be scientifically most exciting—whether it has features of both. Medical investigators from New York to New Guinea were as keenly interested as the veterinarians, because they think scrapie may provide clues to causes and eventual cures for some important and mysterious diseases of man.

First noted in merino sheep from Spain, scrapie has aroused furious controversy many times in its 250-year history. It is the best-looking sheep, the kind that catch the judge's eye at shows, that are most likely to be carriers of scrapie. They have unusually powerful muscle development while young, so they are soon bid in as stud rams. Only in middle life (around 3½ years) do the fatal symptoms develop: enfeebled muscles, itching, the shakes.

Brain to Brain. The argument over scrapie's infectious v. hereditary qualities had simmered for a century before French investigators reported, in 1936, that the disease could be transmitted by inoculating fluid from the brains of afflicted sheep into the brains of healthy ones. The researchers decided that the infectious agent must be an elusive virus.

Now British Veterinarian Herbert B. Parry, whose work is supported by New York's National Foundation for Neuromuscular Diseases, reports convincing evidence from years of study on 1,000 scrapie-ridden sheep that the disease is hereditary, being transmitted by a certain type of recessive gene. If both ram and ewe have two such genes, all their lambs will have scrapie. If one animal has the genes but its mate has none, the "clear" genes will dominate, and the lambs will have no disease. Dr. Parry is still checking a theory that if both parent animals have a single scrapie gene, one out of four of their lambs should get the disease.

Provirus & Gene. Yet Dr. Parry does not knock the virus theory. Rather he speculates that the submicroscopic particle apparently involved may act, in effect, as both gene and virus, transmitting the disease by the mechanisms of heredity and later spreading to attack muscles. It would thus be akin to a "provirus" found in some plants and flies. If this is so, it will be the first instance of such a provirus among higher animals. A provirus could be passed from one sheep to another by inoculation.