Tuesday, December 4, 2012

Uganda closing in on river blindness

In 2007, Uganda announced a bold plan to eliminate river blindness by 2020. The Carter Center’s Moses Katabarwa, a graduate of Emory’s Rollins School of Public Health, has been in the battle from the beginning— and he believes they’re going to win. Photos by Kay Hinton.

By Paige Parvin, Emory Magazine

The River Nile is the longest in the world, moving mightily over more than four thousand miles and through ten African countries before emptying itself into the Mediterranean Sea. For millions it is the source of life and legend, death and mystery, symbol and song—not to mention water, food, transportation, and money. It is at once mythic and utterly real, visible from space and from bridges, banks, and boats.

As the matriarch of Uganda’s many rivers and streams, the Nile holds innumerable secrets, including a tiny black fly that breeds only in swift-moving waters and carries inside it the makings of a particular sort of human misery: onchocerciasis, or river blindness.

Black fly larvae cling to underwater vegetation, developing until they eventually take wing and break the surface as adult flies. 

It’s this fly that Moses Katabarwa, a Uganda native and senior epidemiologist for The Carter Center’s River Blindness Program, has been chasing for more than 20 years. The black fly Simulium—about the size of a Georgia gnat—is unusual in its preference for moving water, since so many of its brethren pests like to breed in warm, stagnant puddles and ponds. Two different types of the fly carry the river blindness parasite, Onchocerca volvulus—one, S. damnosum, dives into flowing waters to lay its eggs, shooting them from its tiny body bundled in a superglue-like substance that sticks them firmly to underwater rocks or vegetation. The other, S. neavei, can lay eggs only in small river crabs and has a shorter flight range than its wily cousin.

When people are bitten by female flies (the males don’t bite), they can become infected with onchocerciasis microfilaria, pre-larval-stage parasitic worms that wriggle their way around under the skin. Like the Guinea worm parasite—another of The Carter Center’s targeted diseases—these worms can breed inside the body; they multiply and sometimes form writhing nodules that can be felt and even seen.

Ojok Charles lost his sight completely after he became severely infected at age 12 with the river blindness parasite. He says he could feel the worms moving in his eyes as the disease progressed.

And they love to migrate up to the eye, where they cause irritation and nerve damage, and eventually, as they die, leave debris that can build up to the point of diminished vision and permanent blindness. Affecting some eighteen million people in Africa and the Americas, the disease is the second-leading cause of preventable blindness in the world.

River blindness infection triggers an immune response similar to that of an allergic reaction, which is why it causes intense itching, swelling, rashes, lesions, and skin discoloration—a pattern commonly referred to as “leopard skin.” Ironically, a strong immune system can produce a more severe reaction.

“If you have an efficient immune system, you will suffer much more,” says Katabarwa. “The more you scratch, the more you want to.”

It takes many fly bites to produce a bad infection—what health workers offhandedly call a high “worm load”—but in rural villages that are situated near swift-moving rivers and streams, it’s not hard to become bait.

Read more in Emory Magazine.

On the trail of black flies

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