Abstract
BackgroundThe development of mosquito nets pre-treated with insecticide, Long Lasting Impregnated Nets (LLINs) that last the life span of the net, is a solution to the difficulty of the re-impregnation of conventional nets. Even if they showed a good efficacy in control conditions, their efficacy in the field, particularly in areas with resistance of Anopheles gambiae to pyrethroids, is not well documented. This study compares wide (Olyset®) and small (Permanet®) mesh LLINs in field conditions, using entomological parameters.MethodsThe two LLINs were tested in a rice-growing area of south-western Burkina Faso (West Africa) with year around high density of the main malaria vector An. gambiae s.s. In the study village (VK6), there is a mixed population of two molecular forms of An. gambiae, the S-form which dominates during the rainy season and the M-form which dominates the rest of the year. The two LLINs Olyset® and Permanet® were distributed in the village and 20 matched houses were selected for comparison with four houses without treated nets.ResultsMosquito entrance rate was ten fold higher in control houses than in houses with LLINs and there was no difference between the two net types. Among mosquitoes found in the houses, 36 % were dead in LLIN houses compared to 0% in control houses. Blood feeding rate was 80 % in control houses compared to 43 % in LLIN houses. The type of net did not significantly impact any of these parameters. No mosquitoes were found inside Permanet®, whereas dead or dying mosquitoes were collected inside the Olyset®. More than 60% of mosquitoes found on top or inside the nets had had blood meals from cattle, as shown by ELISA analysis.ConclusionThe percentage of blood-fed mosquitoes in a bed net study does not necessarily determine net success. The efficacy of the two types of LLINs was comparable, during a period when the S-form of An. gambiae was carrying the kdr gene. Significantly higher numbers of mosquitoes were collected in control houses compared to intervention houses, indicating that the LLINs provided an additional deterrent effect, which enhanced their expected prevention capacity.
Highlights
The development of mosquito nets pre-treated with insecticide, Long Lasting Impregnated Nets (LLINs) that last the life span of the net, is a solution to the difficulty of the reimpregnation of conventional nets
The use of mosquito nets pre-treated with insecticide, Long Lasting Impregnated Nets (LLINs), that last the life span of the net, is a solution to this problem [7]
Mosquito house entering rate and mosquito house location Global house entering rate In total 10,621 mosquitoes were collected during the study (Table 1) and consisted mainly of Anopheles and Culex with unfed, fed, gravid, half gravid, alive or dead mosquitoes from both control and LLINs-equipped houses. 9,078 mosquitoes were caught in control houses by morning capture, while only 1,543 mosquitoes were collected in either Olyset® or Permanet® LLINs-equipped houses during night and in morning capture
Summary
The development of mosquito nets pre-treated with insecticide, Long Lasting Impregnated Nets (LLINs) that last the life span of the net, is a solution to the difficulty of the reimpregnation of conventional nets. Even if they showed a good efficacy in control conditions, their efficacy in the field, in areas with resistance of Anopheles gambiae to pyrethroids, is not well documented. The use of mosquito nets pre-treated with insecticide, Long Lasting Impregnated Nets (LLINs), that last the life span of the net, is a solution to this problem [7]. Two LLINs are available and have been preliminarly recommended by WHO for malaria prevention: the Olyset® [8] net, made of polyethylene netting material (mesh 20 holes/cm2) with permethrin (2% of concentration) incorporated into the polymer before monofilament yarn extrusion, and the Permanet® [9] net, made of polyester netting material (mesh 25 holes/cm2) with deltamethrin incorporated (55 mg ai/m2) in a resin coating of the fibers
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