Malaria -- Effective insecticide-repellent synergy against mosqui...( effects on the mosquitoes. However onl...)

effects on the mosquitoes. However, only the association between the insecticide and the standard repellent produced a synergistic effect that inhibited the mosquito from taking its blood feed. A synergistic effect was also observed with regard to the treatments residual efficacy which is several months longer than that of either agent applied alone. The advantage of the synergistic property of these combinations is enhanced by the fact that it significantly reduced the necessary effective doses against the mosquitoes (about 6 times that of the insecticide applied alone), to attain an efficacy equivalent to that of deltamethrin.

The nets treated with the two mixtures in the laboratory were subsequently tested in field trials, in the rice-growing area 40 km North of Bobo-Dioulasso, in Burkina Faso. This area has the specificity of harbouring two different forms of Anopheles gambiae. The first appears in May and June in the rice-fields. It shows no resistance to pyrethroids. The second emerges in September and October in puddles left by monsoon rains. These do show resistance to these insecticides. As expected, the usual pyrethroid-treated nets turned out to be effective only against non-resistant mosquitoes of the first population. Conversely, the nets pre-soaked with non-pyrethroidrepellent combinations proved excellent protection for the people of the local villages, whatever the population of mosquitoes present. Nevertheless, their residual efficacy (about 15 days) in real conditions did not match the researchers expectations. The team consequently envisage working in conjunction with a company able to devise a system for encapsulating the mixture to prolong the residual life of treated mosquito nets.

The efficacy of these mixtures between organophosphates and repellents therefore opens up a new pathway towards controlling pyrethroid-resistant malaria vectors. In the long term, the researchers plan to test their method on mosquitoes resistant to tw
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Contact: Gregory Flechet
fichesactu@paris.ird.fr
33-014-803-7607
Institut de Recherche Pour le Dveloppement
17-Jul-2007

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