Abstract
BackgroundIn a large cluster randomized control trial of insecticide-treated bed nets (ITN) in Western Myanmar the malaria protective effect of ITN was found to be highly variable and, in aggregate, the effect was not statistically significant. A coincident entomological investigation measured malaria vector abundance and biting behaviour and the human population sleeping habits, factors relevant to ITN effectiveness.MethodsEntomological surveys were carried out using different catching methods to identify potential malaria vector species and characterise their biting habits. The salivary glands were dissected from all female anophelines caught to identify sporozoites by microscopy.FindingsBetween 1995 and 2000 a total of 4,824 female anopheline mosquitoes were caught with various catching methods. A total of 916 person nights yielded 3,009 female anopheline mosquitoes between 6 pm and 6 am. Except for Anopheles annularis, which showed no apparent preference (51% outdoor biting), all major species showed a strong preference for outdoor biting; Anopheles epiroticus (79%), Anopheles subpictus (72%), Anopheles maculatus (92%), Anopheles aconitus (85%) and Anopheles vagus (72%). Most human biting occurred in the early evening with the peak biting time between 6 pm and 7 pm (35%). Overall 51% (1447/2837) of all bites recorded were between 6 pm and 8 pm. A large proportion of children were not sleeping under an ITN during peak biting times. Only one An. annularis mosquito (0.02%) had malaria sporozoites identified in the salivary glands.ConclusionsPeak vector biting occurred early in the evening and mainly occurred outdoors. The limited efficacy of ITN in this area of Western Myanmar may be explained by the biting behaviour of the prevalent Anopheles mosquito vectors in this area.
Highlights
In a large cluster randomized control trial of insecticide-treated bed nets (ITN) in Western Myanmar the malaria protective effect of ITN was found to be highly variable and, in aggregate, the effect was not statistically significant
The limited efficacy of ITN in this area of Western Myanmar may be explained by the biting behaviour of the prevalent Anopheles mosquito vectors in this area
From 16 November to 1 December 1995, 1382 female Anopheles were caught with four different catching methods in the Dabhine area; 94 female Anopheles were caught with Human biting catches (HBC) (32 unfed, 58 blood-fed and four gravid)
Summary
In a large cluster randomized control trial of insecticide-treated bed nets (ITN) in Western Myanmar the malaria protective effect of ITN was found to be highly variable and, in aggregate, the effect was not statistically significant. Declining malaria transmission in much of Southeast Asia has led to a transition in policy objectives from one of malaria control to complete elimination [1]. This ‘endgame’ is likely to require more precision in the targeting of interventions. Insecticide-impregnated bed nets (ITN) have proved very effective in highly endemic areas and have contributed substantially to lower childhood malaria morbidity and mortality. Whether ITN are beneficial in the context of low, unstable
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