When Merck & Co., the United States pharmaceutical giant, announced 10 years ago that it had found a drug that could prevent onchocerciasis, one of the leading causes of blindness in Latin America and Africa, and that it would donate the medicine "wherever needed for as long as needed," it appeared that the last barrier to conquering this disease had fallen.
But not quite. Distributing the medicine to people in remote areas has proven more difficult than expected in Latin America. It took years of effort, and an $18 million program to establish sustainable distribution systems before significant numbers of people began to benefit from the new drug.
The Onchocerciasis Elimination Program for the Americas (OEPA) recently reported that teams in Brazil, Colombia, Ecuador, Guatemala, Mexico and Venezuela distributed the medicine to about 200,000 people in 1996, 60 percent of their goal. In all, coverage was 98 percent in the high risk areas of Latin America where the effects of the disease are most severe.
According to OEPA officials, there have been no new cases of the disease in coastal Ecuador for more than a year and none in Oaxaca State, Mexico, for more than two years. Colombia is on the verge of eliminating the disease.
"We are very enthusiastic about the possibility of eliminating clinical manifestations (blindness and skin disease) of onchocerciasis in Latin America by our goal of year 2007," says OEPA Director Edmundo Alvarez.
Fly vectors
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Onchocerciasis is caused by a parasitic worm that is transmitted between humans by a small blood-feeding blackfly that breeds in fast-flowing streams and rivers.
Adult worms, the thickness of a human hair, can grow a half-meter long in human hosts. They are usually encapsulated by fibrous tissue, forming nodules that are often visible under the skin on the head, neck or body.
It is not the worms themselves, but rather the millions of tiny offspring, called microfilaria, which an adult worm produces during its 12 14-year ‘lifespan, that cause the damage. They migrate throughout the host's skin, producing scaling and itching that has been described as "poison ivy 24 hours a day," and to the eyes, where they create lesions that can result in permanent visual loss and blindness.
Efforts to eradicate the disease-carrying blackfly with insecticides proved expensive and unsuccessful in the Americas. In the late 1970s, scientists at Merck & Co. discovered that one of its antiparasitic medicines for livestock, ivermectin, appeared to be effective against the microfilarial stage of onchocerciasis. Until then, the only medical treatment for river blindness, the common name for onchocerciasis, was by intravenous chemotherapy, which had severe side effects and was expensive.
Clinical field trials conducted by the World Health Organization in Africa and Guatemala in the 1980s proved that ivermectin killed the microfilaria produced by the adult worms. It also suppressed the worms' reproduction for about a year, thus halting progression of the disease in an infected person and interrupting its transmission to others during that period. Trials indicated that if 95 percent of the people in an affected area take ivermectin once a year for a 12 14-year period (the lifespan of the adult worm), the disease can be eliminated, perhaps even eradicated.
Mexico started its elimination program in 1990, and Ecuador and Guatemala followed in 1991. But the other three countries lagged behind. In 1994, the IDB joined a group of donors, including the Pan American Health Organization, the River Blindness Foundation, and the Centers for Disease Control, to finance a five-year program to help all six countries establish sustainable mass distribution systems. Head offices for the Onchocerciasis Elimination Program in the Americas were established in Guatemala, which has 31 percent of all cases of river blindness disease in Latin America.
The IDB's $4 million grant has been used to train teams of health workers, purchase medical equipment and four-wheel drive vehicles and boats to access remote areas, and for mapping and epidemiological studies to determine areas of concentration and to chart success.
Distribution of the medicine has not been easy. At first, health workers had to convince people that they actually needed to take the medicine.
"For example, if they got a bump under their skin, they would say it was from a blow received in a fall," says Dr. Rodolfo Zea, epidemiologist for Guatemala's Ministry of Health. "If they had a vision problem, they said it was caused by sap that dripped on them from some plant or tree."
Another problem was that some people experienced itching or swelling reactions to the medicine when they first took it, side effects that were worse than the early symptoms of the disease. Their friends were then afraid to take the medicine themselves.
In Ecuador, social workers developed a board game to help educate people about onchocerciasis. The winner would teach the losers more about the disease the next day. "Education is one of the main reasons Ecuador has nearly 100 percent coverage in its endemic areas," says Dr. Guillermo Zea, OEPA's deputy director and Rodolfo Zea's brother. "We are changing people's perceptions of the disease and its treatment," he said.
"I think things are going very well in Latin America because the governments are committed," says Frank Richards, deputy director of the Global 2000 River Blindness Program at The Carter Center in Atlanta, Georgia, U.S. "But I worry about the sustainability of this opportunity to rid the Americas of river blindness. Onchocerciasis is not a high priority health problem in these countries, and there's always the need to focus the health resources on malaria, dengue and yellow fever."