River Blindness – A Neglected Disease Transmitted by Blackflies (Simulium spp.)
Depigmentation of skin
The World Health Organization (WHO) operated a prolonged campaign to control the vector of river blindness (Onchcerciasis) in the Savannah of nine West African countries from 1974, with the primary objective of controlling the disease and secondly to enable economic development of the area. The constant biting of flies, especially in the cooler early morning or late afternoon made it impossible for people to grow crops. The Onchocerciasis Control Programme (OCP) jointly sponsored by WHO, the World Bank, the United Nations Development Programme and the UN Food and Agriculture Organization, and supported by a coalition of 20 donor countries and agencies was planned to last 20 years due to the lifetime of the parasite in people. The disease is caused by parasite Onchocerca volvulus, a small filarial worm that initially is in the skin and causes severe itching, and skin changes that include depigmentation and skin atrophy, but as the number of worms increases it can invade the eye and cause blindness.
Blind man with his wife
The vector is a small fly (Simulium damnosum and other species) which has an aquatic larval stage, breeding in turbulent “white water”. The OCP began by identifying the areas of rapids and treated these from aircraft with the larvicide temephos, applied weekly upstream of rapids so that the chemical dispersed across the width of the river and was active for 50 km downstream. Prolonged use of temephos led to selection of larvae resistant to the insecticide, so the biopesticide Bacillus thuringiensis israelensis (Bti) was sprayed as an alternative treatment, although several other insecticides were evaluated to determine their effectiveness. It was considered that treatment over at least 14 years was needed to take account of the life expectancy of adult worms and microfilariae. Some children born after the larviciding started proved to be uninfected and in 1987, Merck &Co Inc. decided to donate ivermectin in Mectizan tablets that had been shown to be effective against the parasite, aiming to eliminate onchocerciasis. From 1987, ivermectin was combined with aerial larviciding and this reduced transmission of the disease.
Outside the OCP area, an African Programme for Onchocerciasis Control (APOC) was launched in 1995 in 19 African countries and was based mainly on mass drug distribution of Mectizan tablets to health communities over a 12–15 year period. The aim was to establish an effective and self-sustaining drug distribution system. Nevertheless, in many areas with blackflies in Africa, the nuisance of multiple bites and severe itching continued to have an adverse effect on villagers and many migrated to towns away from the river areas.
APOC was closed in 2015, but was replaced by the Expanded Special Project for Elimination of Neglected Tropical Diseases (ESPEN) in 2016 to promote an integrated approach to tackling onchocerciasis, along with four other high-burden neglected tropical diseases, including lymphatic filariasis, trachoma, schistosomiasis and soil-transmitted helminthiases.
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This is an extract of the full article published in: Outlooks on Pest Management – August 2017 issue.
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Authors: Jane Nchangnwi Che, Pierre Nkot Baleguel, Pierre Didier Baleguel, Graham Matthews
Category: Public health
