[Control of onchocerciasis vectors in West Africa: description of the logistics adapted for a large-scale public health program]. / La lutte contre les vecteurs de l'onchocercose en Afrique de l'Ouest: description d'une logistique adaptée a un programme de santé publique de grande envergure.

The Onchocerciasis Control Programme (OCP) in West Africa, launched in 1974, includes 11 participating countries and covers more than one million square kilometres. The aim of the OCP is to control blinding onchocerciasis (river blindness) which is caused by the savannah strain of Onchocerca volvulus transmitted by the Simulium damnosum complex. There is no effective macrofilaricide, so vector control to prevent the transmission of the parasite remains the method of choice, despite the availability of ivermectin, a drug which controls ocular morbidity. The potential value of vector control has been demonstrated by the original programme: 14 years activity has eliminated the disease as a public health problem in the areas included. This strategy requires adapted logistical support involving (i) widespread insecticide coverage (27,000 km of river are treated by the OCP during the rainy season), (ii) frequent (weekly) application of larvicide and (iii) prolonged intervention due to the life-span of the worm in the human reservoir, estimated to be approximately 14 years. We describe the vector control operations and their organisation 20 years after the initiation of the OCP. The OCP can be divided into 5 areas of logistic activity. The first covers activities involving insecticide and fuel management for the OCP as a whole: assessment of the requirements for the following year, ordering from insecticide and petrol suppliers, stocking fuel and insecticide at the depots covering the area. The second activity is the treatment of rivers with insecticide. This includes treating the ground with larvicide, the aerial operations run by an independent company supplying 12 helicopters on contract to the OCP, and use of satellite beacons for retransmitting of hydrological data. The third activity is monitoring the impact of larvicides on both the target (adult and larval S. damnosum) and on other fauna (fish, crustaceans and other insects). The fourth activity is field data collection and its processing. This involves a data transmission network to facilitate stock management insecticide application and entomological and hydrological surveillance using computer systems. The fifth activity is the coordination of vector control operations, technical and administrative staff and estimations of the funds available to the Vector Control Unit. The logistic aspects of other large-scale-insect-control programmes world-wide are considered, and the possibility of using the OCP as a model for such programmes (both public health and agricultural) is assessed.

The vectorial efficiency of Simulium yahense populations in south-eastern Ghana.

Adult female Simulium yahense were identified amongst catches of S. damnosum s. 1. caught at Tsatsadu Falls and Wegbe in south-eastern Ghana. Dissections of stained flies to assess the species' role as a vector of onchocerciasis in the region revealed as many as 357 L3 per 1000 biting flies in a sample from Wegbe. When the data from the two sites were combined 154 L3 per 1000 biting flies and 315 L3 per 1000 parous flies were recorded. The values for wet season samples were about 12% higher than those for the dry season. The results are discussed in relation to other studies of S. yahense populations and regarding the species' recent spread in Ghana and Togo.

Distribution of Simulium yahense after larviciding activities in the southern extension of the Onchocerciasis Control Programme.

The distribution range of Simulium yahense in the Eastern Operational Area of the Onchocerciasis Control Programme increased after larviciding treatments were started in 1988, to control important Simulium damnosum s. 1. vectors of onchocerciasis. A distribution map indicating the extended range is drawn and the importance of this expansion of S. yahense to disease transmission discussed.

Seasonal variation in onchocerciasis transmission by Simulium squamosum at perennial breeding sites in Togo.

Analyses of data collected routinely by the World Health Organization Onchocerciasis Control Programme in West Africa showed that the transmission of onchocerciasis by Simulium squamosum at Amou-Oblo, in Togo, was maximal in the dry season. Mean monthly transmission potentials ranged from 10.4 in August to 519.6 in February. Infectivity in terms of numbers of L3 larvae in the head per 1000 parous flies was highest in March. Additional, more detailed, studies involving the staining of flies from Amou-Oblo, Djodji and Tinkiro confirmed these seasonal trends but also revealed significantly higher rates with L1/L2 larvae in the dry season. The results are discussed in relation to seasonal changes in fly numbers, fly longevity, fly size and man-fly contact rates.

[Evaluation of control measures against Simuliidae in the framework of the OCP (Onchocerciasis Control Program)]. / Evaluation des moyens de lutte contre les simulies dans le cadre du programme OCP (Onchocerciasis Control Programme).

To control the vector S. damnosum s.l., the Onchocerciasis Control Programme in West Africa (OCP) uses larvicides which are sprayed mainly by air. Despite the more or less reversible resistance of some species of the S. damnosum complex to the organophosphorus compounds (temephos and chlorphoxim), the Programme has succeeded in finding effective replacement insecticides. These larvicides, which are used in rotation, taking into account the river discharges, blackfly species present, and their susceptibility to the different insecticides, have made it possible to maintain the good results obtained by the Programme. Through vector control alone, OCP has been able to bring the disease under control in more than 90% of the initial area. Resettlement is taking place on the fertile lands which were formerly deserted because of onchocerciasis and many socioeconomic development projects are currently being carried out. The extensions made towards the western and the southern parts of the Programme area and the use of ivermectin, a microfilaricide, will enable these results to be improved further.

The Beffa form of Simulium soubrense of the S. damnosum complex in Togo and Benin.

The Beffa form of Simulium soubrense Vajime & Dunbar, a member of the S. sanctipauli sub-complex of the S. damnosum complex, was found breeding throughout rivers in the Togo-Benin Gap, as far north as 9 degrees 30'N. Its distribution changed with the season. In southern Togo there were seasonal fluctuations in the relative abundancies of the Beffa form and of S. damnosum/S.sirbanum. There was considerable temporal and regional variation in the frequencies of different colour morphs of adult flies. The flies in Benin tended to be darker. Infections with Onchocerca volvulus (Leuckart) appeared to be independent of the host's colour morph category. Larger flies harboured significantly more first stage Onchocerca larvae but no significant relations with fly size were found for second and third stage larvae.