Eliminating Onchocerciasis after 14 Years of Vector Control: A Proved Strategy

Abstract

From 1976 through 1989, weekly aerial spraying operations against blackflies were carried out along the rivers of a wide savanna area of West Africa (approximately 700,000 km(2)) where onchocerciasis was hyperendemic. The level of endemicity began to decrease significantly after 4 years of vector control and became very low in 1989. This situation has been maintained without any vector control activity or chemotherapy, and no incidence of any new cases has been detected. An ophthalmological study carried out in 2000 has confirmed these good results, showing only cicatricial ocular lesions in the examined population. These results led to the conclusion that 14 years of vector control may achieve long-term elimination of onchocerciasis, even in the absence of chemotherapy, provided that the treated areas are not subjected to any contamination by exogenous parasites carried in infected humans or flies.

Research for control: the onchocerciasis experience*

“…Based on this prediction, vector control was stopped after 14 years in the original OCP area (WHO 1995) and the prediction proved later to be correct. To date, more than 10 years later, this area is still free from onchocerciasis transmission (Hougard et al 2001). An example of the model predictions and the observed epidemiological trends is given in Figure 2 for an onchocerciasis focus along the upper Comoe river in Burkina Faso, which was initially hyper-endemic.…”

Information infrastructures and public goods: Analytical and practical implications for SDI

“…Aerial spraying of the infested rivers was conducted when the conditions were favourable for the vector (the blackfly larvae) to develop. In addition, mass distribution of medication to the infected population proved successful (Hougard et al, 2001).…”

Control of River Blindness in West Africa: Case History of Biodiversity in a Disease Control Program

“…The OCP sought to control Simulium in the initial seven countries using weekly insecticide application of the non-persistent temephos by applying it to breeding sites of black flies in fast flowing rivers by helicopter. Application for a 20-year period (the assumed life span of the adult worm at that time) would ensure that no transmission would occur after pesticide application commenced; therefore, they concluded that, after a 20-year period (later shown to be 12-14 years), both adult worms and microfilaria would have died out and no new infections would have occurred in children born since the control started (Hougard et al, 2001).…”

“…In all but a small number of treatment zones in the initial areas of the program, vector control was stopped in the late 1980s/early 1990s after detailed epidemiological and entomological assessments (see WHO, 1995;Molyneux, 1995;Boatin et al, 1997;Hougard et al, 2001). However, as OCP evolved into the extension areas in the late 1980s, the anti-helminthic drug ivermectin, which is effective against gastrointestinal helminths in the animal health market, proved to be a potent microfilaricide for Onchocerca infections (subsequently donated by Merck & Co., Inc. [White House Station, NJ], as the drug Mectizan Ò ), and became an integral part of OCP control strategy.…”

“…There have been several reviews of OCP that reflect several different aspects of its complex operations over almost three decades (e.g., Samba, 1994;Molyneux, 1995;Boatin et al, 1997;Hougard et al, 1997Hougard et al, , 2001Benton et al, 2002). These publications provide readers with a detailed background of key events and decisions in the vector control program and epidemiological changes over the time frame of its activities.…”