Brain killer stable in soil.

Brain killer stable in soil

It reads like a script from a grade-B horror movie: A mysterious infectious agent turns the brains of cattle and sheep spongy, forcing ranchers to bury the dead animals in mass graves.

Yet the story is true, and a new report adds a frightening twist: The agent seems to persist underground, its lethal powers intact.

Scientists have yet to nail down the virus-like particle responsible for bovine spongiform encephalopathy in cows and scrapie in sheep, but whatever causes these diseases appears to remain infectious even after three years in soil, according to Paul Brown and D. Carleton Gajdusek of the National Institute of Neurological Disorders and Stroke. Their finding implies that the current practice of burying infected carcasses may be imprudent.

In an experiment that has stirred, in Brown's words, "a little electricity" among scientists worried about environmental contamination, the researchers loaded soil-filled pots with doses of the infectious material and buried the pots in Brown's backyard garden. Three years later, they dug up the pots. Experiments in hamsters confirmed that the material was still lethal, they report in the Feb. 2 LANCET.

Brown says the degree of infectiousness remaining after three years leads him to suspect that the material could remain deadly in soil for a decade or more. And although most infected animals are buried with corrosive quicklime, he doubts that ranchers use enough of the chemical to kill all the infectious particles. Brown recommends research to determine the concentration of corrosives needed to render infected carcasses harmless.

"I would at least think that burial sites ought to be identified so someone doesn't 10 years down the road use it as a pasture," he says. In the past, he notes, flocks of sheep have developed scrapie after grazing in areas where infected carcasses had been buried.

Two researchers studying the infectious particle told SCIENCE NEWS that while the backyard experiment lacked some scientific rigor, the warnings may prove appropriate.