Science / Medicine : Screwworm Eradicated in N. Africa

The dreaded screwworm, which once ravaged livestock and wildlife in the United States and Mexico, has been eradicated from North Africa by the United Nations Food and Agriculture Organization, a victory that pest control experts say has spared Africa, and probably Europe, a disaster. Weekly for six months, a chartered DC-8 flew from a factory in Mexico to Libya carrying 40 million male screwworm flies that had been sterilized by gamma rays.

Upon their arrival in Tripoli, the males were loaded into a squadron of Twin Otter aircraft, flown to an altitude of 1,500 feet and thrown out of the plane. On the ground, the huge numbers of sterile males pursued and mated with wild female flies, which then laid eggs that were duds, breaking the cycle of infestation. The agency said last week that there have been no new findings of unsterilized screwworms since April.

The insects are parasites of warmblooded animals. The females deposit about 300 eggs on small pre-existing wounds, and when the eggs hatch, the wormlike larvae burrow, or screw, into the living flesh, feeding upon it as they go. They feed on humans as well.

The insects were eradicated in the United States in 1982 and in Mexico last year. Currently, efforts are under way in Guatemala and Belize to push the insects back down the length of Central America. If not eradicated in North Africa, the flies could have spread to Europe, to Tunisia and Egypt and into sub-Saharan Africa.