Blackfly control: what choices after onchocerciasis?

Blackflies are reappearing in areas of West Africa where they used to be controlled with insecticides because they were vectors of the parasite Onchocerca volvulus. Even though they no longer transmit onchocerciasis in these areas they can hinder optimal land use through their biting behaviour. The authors discuss the problems associated with resuming the use of insecticides to control the blackfly and recommend that ground treatment be restricted to areas where it is likely to be effective on a continuing basis. In communities lacking technical and financial resources the only alternative consists of individual protection through the use of repellents or protective clothing.

PIP: Biting insects can be a major inconvenience to people and can even cripple socioeconomic development. Since the transmission of Onchocerca can be blocked by destroying the blackfly vector in its larval stage, blackfly control has been practiced in West Africa since 1975 at the regional level as part of the Onchocerciasis Control Program. Since development of the insect from egg to nymph rarely takes longer than 1 week, spraying is conducted at weekly intervals. Treatments are delivered mainly from the air due to the large number of breeding sites and the difficulty of reaching most of them overland. Vector control remains the preferred approach to onchocerciasis control in regions open to reinfection by blackflies from untreated areas in which the disease is hyperendemic. Aerial spraying, however, has ceased in regions where there is virtually no longer any risk of contracting onchocerciasis. Blackflies are therefore reappearing in areas of West Africa where they used to be controlled with insecticides. Even though these flies no longer transmit onchocerciasis in the areas, their biting behavior can thwart the optimal use of land. With certain exceptions, controlling blackflies is not necessarily the best way of ensuring the long-term development of areas freed from onchocerciasis. Since commercially available products, usually based upon pyrethroids, are too expensive for most communities concerned, and protective clothing is unfeasible due to their high cost and the tropical climate, an inventory of locally-used repellents is being prepared for use.

[The necessity of conducting to the end the activities of vector control in the onchocerciasis control program in west Africa: recall of the stakes and proposal of a minimum budget for the period 1998-2002]. / De la nécessité de mener à terme les activités de lutte antivectorielle du programme de lutte contre l'onchocercose en Afrique de l'Ouest: rappel des enjeux et proposition d'un budget a minima pour la période 1998-2002.

After a brief presentation of the Onchocerciasis Control Programme in West Africa (OCP), the authors realize the health and socioeconomic consequences that could follow a cessation of larvicide treatment before 2002 in the south-eastern and western extensions of the Programme. Taking into account that OCP activities are theoretically supported until 1997, but aware of financial constraints that will probably increase from now to 2002, this paper proposes an a minima estimation of the residual vector control activities for a "phasing out" spread out for five years (1998-2002). These estimations essentially concern the larvicide coverage, the insecticides used, the entomological surveillance, the logistical support and their financial aspects. As far as 48 U.S. $ million amount for 5 years are concerned, the budget allocated for vector control activities should not exceed the third of the global amount allocated to OCP for the actual fourth financial phase of the Programme (1992-1997).

[Importance and role of spreading larvicides on the soil in river beds for the control program against onchocerciasis in west Africa]. / L'importance et le rôle des épandages larvicides au sol dans l'aire du Programme de lutte contre l'onchocercose en Afrique de l'Ouest.

The control of blackfly is based on larvicide spraying in rivers where the insects breed and their larval stages are vulnerable. The first technique for large-scale operations, consists of using aircraft in the same way as for mosquito control and crop protection operations. The second technique, which will be discussed in this paper, consists of ground treatment of rivers, either directly with a container or with a spraying pump or by boat spraying insecticide in cross strip. In areas of West Africa where onchocerciasis is still prevalent, ground treatment is done to support aerial operations and to a lesser extent to control nuisance in areas where the endemicity of the disease is low. In onchocerciasis-freed zones, control of blackfly aims only at suppressing the nuisance in order to enhance the socio-economic development in areas at unfair disadvantage. This distinction is important for determining the responsibilities of various groups. Vector control to interrupt the transmission of onchocerciasis is the mandate of OCP while the control of nuisance is the responsibility, depending on the circumstances, of the private sector, the government and/or village communities. In this paper, we have attempted to highlight the objectives of such treatments, the responsibilities of various groups and the prospects in West African countries located in the Onchocerciasis Control Programme area. We also present the situation of ground larviciding in countries outside the Programme, in temperate as well as tropical conditions, in order to provide some basis for the development of ground treatment strategies in the OCP area.