Is the end in sight for river blindness?

12 World Health • SlstYear, No. 5, September-October 1998 Is the end in sight for river blindness? Daniel E. Etya' ale Onchocerciasis, commonly known as river blindness, is a parasitic disease caused by a filarial worm known as Onchocerca volvulus. The adult worms have a lifespan of some 9 to 14 years and the females produce millions of microfilariae (baby worms), which migrate to the skin of the infected person and cause itching, and to the eyes, where they can cause blind- ness. When a female blackfly bites an infected human and then moves on to bite someone else, the parasite is transmitted to a new victim. These flies breed in fast-flowing streams, and it is near the breeding sites that transmission of the disease is most intense. People who are exposed to the bites of infective flies early in life are especially at risk of being se- verely infected and losing their sight. Men are more exposed than women to these bites, especially fishermen and farmers who work close to the river. Onchocerciasis afflicts more than 18 million men, women and children in 37 countries, principally in sub- Saharan Africa and Latin America, but also in south Yemen. About 125 million people in the world are considered to be at risk, and over 99% of those infected live in Africa. There are two main forms of the disease: the blinding type, mostly found in the savannah belt north of the Equator and the Congo River basin; and the non-blinding type, responsible for relentless itching, with a disfiguring skin disease. Both forms cause great suffering, low economic output, poor school per- formance and social stigmatization. The most severe consequences of onchocerciasis are irreversible eye changes, resulting in impaired vision and ultimately in blindness. About A young Indian child in the Amazona region is given ivermectin to combat onchocerciasis. Wide coverage of all communities concerned with this treatment may make river blindness a disease of the past by the year 20 10. Photo WHO/TDR/M. Edwards one million people today are either blind or severely visually handi- capped, and some 40 OOO new cases of blindness occur each year. In the worst affected communities, over one-third of the adult population and nearly all the male workforce over 40 years of age may already be blind, and their life expectancy is often reduced by ten years. In West Africa, many villages and fertile river valleys have been abandoned for fear of this scourge. Control measures There are two main ways of control- ling this disease. The blackfly may be eliminated by spraying insecti- cides in the breeding sites - a com- plex and expensive method of vector control that has nevertheless been used very successfully since 1974 by the Onchocerciasis Control Programme (OCP) in West Africa. Alternatively, the parasitic worm itself can be targeted by a drug. Since 1987 there has been a safe and effective drug called ivermectin (Mectizan ®), donated by the manu- facturer, Merck & Co, which is suitable for large-scale treatment and needs to be taken only once a year. But because it kills only the microfi- lariae and not the adult worm, it must be taken for many years. Three major regional control programmes are now in operation, all of them closely associated with WHO. In Africa, besides the OCP, which covers 11 countries, there is the African Programme for Onchocerciasis Control, APOC, covering 19 countries. The Onchocerciasis Elimination Programme of the Americas, OEPA, covers six countries of Central and Latin America. In OCP, controlling the blackfly vector has been the main strategy, supplemented where appropriate with ivermectin. Both APOC and OEPA rely on mass treatment with ivermectin. Provided these two programmes can sustain wide coverage with ivermectin treatment of all targeted communi- ties for at least 12 to 15 years, it is reasonable to believe that, by the year 2010, river blindness will have become a scourge of the past in all the countries concerned. • Or Daniel E. Etya'ale is an ophthalmologist with Prevention of Blindness and Deafness, World Health Organization, 121 1 Geneva 27, Switzerland.