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Wormwood: a new crop to combat malaria.

Charles T. Bryson is a botanist--not a medical doctor--yet his work may eventually save millions of lives.

Bryson and colleagues at the ARS Southern Weed Science Laboratory at Stoneville, Mississippi, were asked by the University of Mississippi to develop a weed control system that will help ensure an abundant supply of a new drug to treat malaria.

Scientists at the university's Research Institute of Pharmacy Science were tapped by the World Health Organization (WHO) to study the productivity of various lines of annual wormwood. Studies also explored the isolation of an antimalarial substance from the plant.

Annual wormwood has been used by the Chinese for 2,000 years to treat malaria. Researchers are currently testing a new, refined drug derived from the plant and hope that it can be used worldwide within the next 10 years. But for that to become a reality, wormwood must be produced on a large scale.

"Annual wormwood already grows throughout the United States and is often considered a weed," says Bryson. The woody-stemmed, cone-shaped plant reaches a height of 4 to 8 feet. Most U.S. farmers should be able to grow this potential cash crop.

Wormwood is harvested with a sickle-type machine similar to that used to cut kenaf and sugarcane. Once harvested, the cut plants must be protected from prolonged exposure to the sun's ultraviolet light, which breaks down the antimalarial substance--artemisinin.

Dried wormwood leaves are distilled to extract the artemisillin. To get about 1 gram of the substance, 1,000 grams or 2.2 pounds of the small leaves must be processed.

"At this rate, thousands of acres of wormwood would be needed to maintain a constant supply of the antimalarial drug," says Bryson. "That's why establishing a cropping system for annual wormwood is so important."

But before it can be raised as a crop, farming methods, including weed control measures, must be developed for growers.

From 1985 through 1988, Bryson conducted tests to determine which herbicides would provide the best weed control with the least effect on the wormwood. Researchers first watched the effects of several herbicides on seedlings in growth chamber and greenhouse tests. Results of these experiments were used to narrow the number of herbicides used for field tests.

"Our greenhouse tests and field trials pinpointed three treatment systems that provided about 80- to 90-percent season-long weed control where seedling plants were established," says Bryson. The top three systems all included post-emergence applications of acifluorfen and fluazifop. But a pre-emergence treatment of chloramben provided the best weed control with the least noticeable crop injury, including effect on plant height, fresh weight, and the yield of artemisillin.

Preplant-incorporated trifluralin proved to be the second most effective system; the third included a preemergence application of metolachlor. "Looking just at weed control, without considering the other factors, the chioramben followed by the acifluorfen and fluazifop was again the best system," says Bryson. "The metolachlor treatment came in second, outperforming the trifluralin."

WHO estimates that 110 million people throughout the world contract malaria each year, causing 1 to 2 million deaths. A problem in the United States at the turn of the century, malaria was virtually wiped out by 1955, mainly through the use of DDT on mosquitos. Malaria victims were treated with quinine. But the disease is showing up again in the United States--mainly in Southern California--with 800 to 1,000 cases reported annually.

Malaria is caused by a parasite that is spread by the bite of the female anopheles mosquito. The parasites and mosquitos have apparently developed a resistance to current treatments.

This resistance, coupled with a lack of drugs and doctors in countries where malaria outbreaks are the worst, is why new treatments are needed.

Tests of the drug arteether, made from artemisinin, are now being conducted in Europe. Approval by the U.S. Food and Drug Administration will be necessary before the drug is available in the United States.--By Marcie Gerrietts, ARS.

Charles T. Bryson is at the USDAARS Southern Weed Science Laboratory, P.O. Box 350, Stoneville, MS 38776. Phone (601) 686-5259.
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Title Annotation:research by Charles T. Bryson
Author:Gerrietts, Marcie
Publication:Agricultural Research
Date:Jun 1, 1992
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