World Health Organisation test applied on Culicoides: a multicentric study

The aim of this work is to organize a multicentric assay to compare susceptibilities of Culicoides populations to insecticides (i.e. C. imicola and C. obsoletus sensu stricto). The base line of the World Health Organisation test kit (WHO/VBC81.805) is to expose mosquitoes to papers impregnated with insecticides to detect the resistance of Anopheles (paludism vector) in the field. In a novel approach, the WHO test can be used on Culicoides to assess midges' susceptibility to insecticides. Information on the intrinsic susceptibilities to insecticides is required to assess correctly the existing (or new) formulations of insecticide. This multicentric assay will improve our capacity to experiment by networking and assess the population variability by comparing susceptibilities between different populations of Culicoides. Field-collected midges are trapped alive using an ultraviolet light trap (OVI model, South Africa) and replacing the collection jar with a fine mesh cage. To prevent desiccation, cages are covered with wet papers, wrapped in aluminium foil and retrieved at dawn. It is important to choose the site and period with abundant target species to improve robustness with more individuals. Experiments should be carried out in an insecticide-free environment with constant temperature and humidity, and started a few hours after collection. Insecticide-impregnated papers are rolled and fastened into the WHO kit test tube. About 30 Culicoides (approximately 20 nulliparous females) are collected and transferred to the tube. Tubes are maintained horizontally for an hour (exposure to insecticide). Mortalities are recorded 1 h and 24 h after exposure. One control is performed without insecticide to validate the test. Mortalities are analysed by probit regression to obtain LC50 and LC90 for each population. The test has to be run at least with four concentrations of insecticide, one control and four replicates with samples from the same population. Only nulliparous females are recorded. Insecticide concentrations are given in percentages (WHO standard). In this WHO test, the target species are C. imicola and C. obsoletus s.s., and the active ingredient used is deltamethrin at doses 0.005, 0.001, 0.0005 and 0.0001%. Data will be centralized and analysed by EID-Méditerranée (France), and results will be given back to the partners and published. Future studies could focus on comparing the four deltamethrin concentrations on other species and testing Culicoides susceptibility to other components. (Texte intégral

Lutte anti-vectorielle ciblée dans le contrôle de la trypanosome : l'exemple de Sidéradougou

L'approche développée au Cirdes pour le contrôle de la trypanosomose animale a permis de réaliser une lutte ciblée aux points de transmission dans la zone de Sidéradougou (Burkina Faso). Elle vise à contrôler les densités de vecteurs pour briser les cycles parasitaires. De coût et de technicité réduits, elle pourrait être assumée par les éleveurs. Dans deux zones (Bagouera et Sinogdjan), des écrans imprégnés (triflumuron ou ß-cyfluthrine) ont été posés pendant la saison sèche et des solutions insecticides pour-on ont été utilisées pendant l'hivernage. Un troisième site (Péfrou) permet de suivre une situation sans intervention, mais sous l'influence des sites de lutte adjacents. La lutte ciblée, évaluée par suivi entomologique et suivi d'animaux sentinelle, a entraîné la disparition des glossines de Sinodgjan, la chute des densités à Bagouera (97 %) et Péfrou (91 %) et le quasi arrêt de la transmission parasitaire