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Fighting the insect enemy in Somalia.

When he anived in Somalia last December, Lt. Armando Rosales was just as concerned about buzzing insects as he was about whistling bullets.

As a participant in die Operation Restore Hope mission to bring food to starving Somalis, Rosales faced an array of deadly insects. In Somalia, mosquitoes transmit a parasite that causes malaria, a disease that can be as fatal as a warlord's well-placed bullet. Ticks, flies, and other insects also spread dangerous diseases.

As a medical entomologist with die Armed Forces Pest Management Board in Washington, D.C., Rosales was well aware of those dangers when he arrived in Somalia for a 3-month tour with a medical team assisting an engineering squadron.

Within minutes after landing on Dec. 17, Rosales instructed the 70 people in the squadron to spray their clothing and bed mosquito nets with permethrin - an insecticide - and to cover their exposed skin with a cream containing a repellant called deet.

"I considered those to be the number-one defense against insect-borne disease," he says. "And, to my knowledge, when we left on March 7, there were no cases in our squadron."

That's good news to Carl E. Schreck and fellow Agricultural Research Service scientists who have developed deet and permefthrin to protect soldiers. ARS scientists discovered deet in the 1950's and began developing permethrin in the 1970's. It's also good news for U.S. forces in Somalia, because an ARS computer model predicted that thousands of soldiers would have gotten malaria without the protection that deet and permethrin gave.

Schreck, an entomologist with the agency's Medical and Veterinary Entomology Research Laboratory in Gainesvilie, Florida, says soldiers now use deet cream that lasts longer than the earlier liquid form that sometimes irritated the skin. The cream was developed in the late 1980's under an ARS, military, and private-sector project.

"In field studies, deet cream has been effective for 7 to 10 hours under worst-case conditions in the Florida Everglades, where mosquitoes and other insects are numerous," Schreck says.

Campers and other people who love the insect-infested outdoors are also benefiting from deet in commercial insect repellants. Of the 212 products the U.S. Environmental Protection Agency has registered for this purpose, 192 contain deet.

Permethrin - a synthetic form of the natural pyrethrum insecticide - doesn't cause irritation, is odorless, resists breakdown in sunlight, and doesn't readily come out when clothes are washed. Soldiers can spray it on their clothing, netting, and tents, or it can be soaked into the material. "If you're wearing permethrin-treated clothes, you're a walking mosquito killer," Schreck says.

A division of the Graniteville Company, a South Carolina textile mill, has received a patent to make a tent fabric coated with permethrin.

The deet and permethrin protections appear to have been effective - not only in Rosales' squadron, but also among U.S. forces overall. As of mid-March, there were only 47 confirmed cases of malaria among U.S. troops in Somalia, according to an Army Surgeon General report.

"Most cases were because people didn't use the deet cream or permethrin material or didn't take anti-malarial drugs," Rosales says.

The ARS computer model had predicted that if no preventive measures had been taken, there could have been as many as 3,000 cases of malaria among 16,000 troops stationed in Baidoa and more than 7,000 cases in Mogadishu over a 60-day period. The malaria simulation model (MALSIM), developed by agricultural engineer Danel G. Haile at the Gainesville lab, predicts how many cases of malaria can be expected based on weather patterns, control measures, personal protection, and other factors.

MALSIM's numbers for Somalia show how dangerous it could be for U.S. troops there - if not for deet and permethrin. "As long as they use these properly, they shouldn't have a problem," Schreck says.
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Author:Adams, Sean
Publication:Agricultural Research
Date:Aug 1, 1993
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