River blindness “curse” lifted

Editor’s note: Dr. Vincent Resh of the University of California at Berkeley addressed the distinguished, long-lived Commonwealth Club of San Francisco on August 22, 2007. Below is a column by Resh which appeared in the San Francisco Chronicle a few days before the speech, covering much of the same material.

Resh tells the story of a public health victory in Africa against a disease called river blindness. People victimized are made blind by a parasitic worm which lives in the victim’s eyes. I relate it here because Resh tells how the victory is achieved without resorting to the use of destructive DDT, which had been proposed. Note carefully what Resh says about DDT. This is one more chunk of evidence against the broadcast use of DDT, a story in support of the ban on DDT imposed in the U.S. since 1972. Rachel Carson was right.

  • Vincent H. Resh has been a professor of entomology at UC Berkeley since 1975. He was the senior environmental adviser for the onchocerciasis control program.

This article appeared on page E – 5 of the San Francisco Chronicle.


River blindness ‘curse’ lifted

Sunday, August 19, 2007

Insect-transmitted diseases typically come to our attention through local news reports of the threat of West Nile virus or of dengue fever in our neighborhoods. The works of the Gates Foundation have made us more aware of malaria, the mosquito-transmitted disease that kills well more than a million people each year. But there are scores of insect-transmitted diseases that affect humans, and the insects responsible for many of them live in water.

River Blindness Cycle, Carter Center - Alberto CuadroClick on thumbnail image for a chart showing the life cycle of river blindness from the Carter Center, by Alberto Cuadra

DDT and its descendents were initially effective in controlling the water-dwelling vectors of human diseases. However, the effects of these insecticides on environmental health also had significant, indirect effects on human health. The fish in rivers, which are the main protein source for humans in most developing countries, were drastically reduced by these poisons.

The control of one of these diseases, onchocerciasis or river blindness, in West Africa is a true success story for a continent where reports of success stories are typically in short supply. In the 1970s, as many as 30 percent of the villagers living along the fertile rivers in West Africa would go blind from this disease. People expected that blindness was part of their normal life cycle.

Humans don’t die from river blindness but it extracts a large toll on subsistence villages where people are living on less than $1 per day. A particularly unfortunate consequence of this disease has been the abandonment of affected river valleys, and their high agricultural productivity, because these areas were considered to be “cursed” by river blindness.

Onchocerciasis is caused by a round worm that is transmitted among humans by black flies. The fly’s descriptive name, Simulium damnosum, reflects its annoying and painful biting habits. The disease occurs in Africa and Latin America but more than 99 percent of the cases occur in West Africa. The Onchocerciasis Control Program, established in 1974 and led by the World Health Organization of the United Nations, has controlled this disease in 11 West African countries. The program’s success was from reducing numbers of the black-fly vector that transmits the disease-causing worms by applying insecticides to over 30,000 miles of rivers spread over some 500,000 square miles. Applications were weekly and, in some cases, had to last for 20 years.

More recently, protection from this disease has been enhanced by ivermectin drugs, which is the drug we use to treat dog heartworm in our pets, to kill the worms already in people’s bodies. More than 7 million West Africans received the drug annually, which was given by the drug company Merck for free. Because the widespread application of insecticides could have had major environmental (and consequently indirect human health) effects, the program included the first large-scale “river health” monitoring program to study any effects from long-term applications of insecticides on the fish and the insects that they eat. In the end, reliance on biological insecticides such as the bacteria Bti, which is also widely used in mosquito control in the Bay Area, left no reduction in fish production or diversity in the insecticide-treated rivers.

But the real success can be seen through the numbers. The World Health Organization and the World Bank estimate that because of onchocerciasis control in West Africa alone: 40 million people have been protected from river blindness and an estimated 600,000 cases of blindness have been prevented in the 11 countries treated; 60 million acres of arable land in previously infected river valleys has been open to resettlement and cultivation; and food for an estimated 17 million people are now being grown. This was achieved for a cost of about $12 per person protected.

In the 15 years I worked as part of this program, one experience has stayed with me more than any other. The Dutch government gave us money to give to the Africans who distributed ivermectin in their villages. However, they didn’t want money. What they asked for was salt and soap – one to use as a food preservative, the other to reduce infections. Since then I’ve thought that these items are what really matter in life.

Copyright of title and some material by the San Francisco Chronicle, 2007; other copyright may be held by Dr. Vincent H. Resh. This is a fair use of material for public education, at no charge and no profit.

Head of a blackfly, the disease vector for river blindness - Natural History Museum, London

Head of a simulian blackfly, the disease vector for river blindness. Image from the Natural History Museum, London

Update, 1-30-2011:  Breakthroughs, a newsletter from the College of Natural Resources, University of California at Berkeley, Summer 2008, “Entomologist Vincent Resh has leveraged science and diplomacy to help bring an epidemic under control along 30,000 miles of West African rivers”

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