Comm Eye Health Vol. 14 No. 38 2001 pp 17 - 19. Published online 01 June 2001.

Onchocerciasis: impact of interventions

Bjorn Thylefors MD

Former Director, Programme for the Prevention of Blindness and Deafness, World Health Organization, Geneva, Switzerland

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The disease

Onchocerciasis, more commonly known as ‘river blindness’, is a parasitic, blinding disease, endemic in 30 African and six Latin American countries. Recent estimates point to around 18 million people infested with the parasite, the nematode Onchocerca volvulus, and some 270,000 who are blind from ocular complications.1

Control efforts

Since before 1972, onchocerciasis had been subject to attempted control of transmission, beginning in the late 1940s in Africa. A unique success was the elimination of transmission of Onchocerca volvulus in one valley in Kenya, through the use of DDT. This result was lasting because of the ecological situation within a very isolated focus. However, similar attempts of vector control in other foci in West Africa had all failed because of re-invading flies from nearby endemic areas. At a meeting in Tunis in 1968, the idea of a large vector control zone in the Volta River Basin Area, which could encompass all known transmission and breeding sites and rule out re-invasion, was introduced. This was the philosophy behind the creation of the Onchocerciasis Control Programme (OCP) in West Africa, which was planned by WHO from 1972 to 1974, with joint input from the United Nations Development Programme (UNDP), the Food and Agricultural Organization (FAO) and the World Bank. OCP started its aerial operations for vector control in seven West African countries in early 1975, eventually covering an area of 1,235,000 km2and 50,000 km of river stretches. It was then expanded to 11 countries, and has undergone significant changes in terms of strategies and operations for control of onchocerciasis. It soon became clear that the problem of re-invading flies could occur, even in the new, vast programme area. After a few years, resistance by Simulium to the first insecticide used (temephos, or Abate®) became evident in certain foci. Despite these difficulties, OCP managed to continue its operations, with rotational use of other insecticides. When ivermectin (Mectizan®) was made available by Merck & Co., a new strategy was added; the distribution of ivermectin to affected populations in certain foci. It had been demonstrated that ivermectin, taken in annual doses, had a pronounced suppressive effect on onchocercal disease,2 also reducing the microfilarial skin load down to very low levels for many months. A number of studies have been carried out on delivery systems and cost recovery for ivermectin delivery to those in need.3 It became possible to control both the disease and contribute to transmission interruption in affected areas.

Twenty-five years of progress

OCP has celebrated its 25th anniversary. It is a hugely successful programme, which has protected approximately 11 million children against onchocerciasis – and around 500,000 people have been saved from blindness. In addition, there has been tremendous socio-economic gain in the resettlements of new communities in the previously infested areas – some 250,000 km2 of ‘new’ land has been resettled and is now being cultivated. New agricultural and (ther development schemes in these onchocerciasis-freed areas have contributed to an Economic Return Rate of around 18%, which is significant. OCP is now preparing for its closing down by the end of 2002, although surveillance activities for possible recrudescence of disease will continue.4 Much work has also been done to transfer the necessary capability to Ministries of Health in member countries.

In parallel with the OCP developments, making use of ivermectin, new control programmes were also planned. In Latin America, where onchocerciasis is endemic in six countries (but with less blinding potential) a new project was created – the Onchocerciasis Elimination Programme in the Americas (OEPA). In that setting, with different and less ‘effective’ vector flies, the regular dosing of populations by means of ivermectin is likely to lead to complete interruption of transmission. The total elimination of the disease is possible, and good progress is being made in this direction.

In Africa, a new African Programme for Onchocerciasis Control (APOC) was established in 1995, creating a partnership with a group of dedicated non-governmental organizations, in addition to the agencies already involved in OCP. APOC covers onchocerciasis in the remaining 19 endemic countries in Africa, in addition to the 11 OCP countries. APOC has made rapid progress in implementing Community Directed Treatment with Ivermectin (CDTI), through national task forces in all participating countries. The CDTI strategy promotes cost-effective and large-scale ivermectin distribution to populations in need in endemic areas. Thus, the present estimated annual treatments are in the order of 15 million cases in the OCP and APOC areas.

It can be safely stated today that the elimination of onchocerciasis as a public health problem is now within reach. The ongoing and planned operations in the three control programmes (OCP, OEPA and APOC) will cover all disease foci, where intervention is necessary. Thus, by the year 2010, it will be possible to conclude that visual loss due to this dreadful disease will disappear. This would be one of the major achievements within the Global Initiative for Elimination of Avoidable Blindness, launched in 1999 by WHO in collaboration with a dedicated group of non-governmental development organizations, under the theme of ‘VISION 2020: The Right to Sight’. The Initiative, which focuses on five major causes of avoidable blindness, is an outstanding effort for global action and partnership in the prevention of blindness. The possibility of eliminating onchocerciasis as a public health and socio-economic obstacle to development, is perhaps the first victory in sight for the ‘VISION 2020′ Global Initiative.

References

1 World Health Organization. Onchocerciasis and its Control. Report of a WHO Expert Committee on Onchocerciasis. TRS No.852, WHO, Geneva, Switzerland. 1995.

2 Abiose A. Onchocercal eye disease and the impact of Mectizan treatment. Ann Trop Med Parasitol 1998; 92: S11-S22.

3 Amazigo U, Noma M, Boatin BA, Etya’ale DE, Seketeli A, Dadzie KY. Delivery systems and cost recovery in Mectizan treatment for onchocerciasis. Ann Trop Med Parasitol 1998; 92: S23 – S31.

4 World Health Organization. 25 OCP years (1974-1999). Onchocerciasis Control Programme in West Africa. Ouagadougou, Burkina Faso, 1999.