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Randomized Controlled Trial
. 2013 Oct 11:12:364.
doi: 10.1186/1475-2875-12-364.

Entomological determinants of insecticide-treated bed net effectiveness in Western Myanmar

Frank M Smithuis  1 , Moe Kyaw Kyaw, U Ohn Phe, Ingrid van der Broek, Nina Katterman, Colin Rogers, Patrick Almeida, Piet A Kager, Kasia Stepniewska, Yoel Lubell, Julie A Simpson, Nicholas J White
Affiliations
Randomized Controlled Trial

Entomological determinants of insecticide-treated bed net effectiveness in Western Myanmar

Frank M Smithuis et al. Malar J. .

Abstract

Background: 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. A coincident entomological investigation measured malaria vector abundance and biting behaviour and the human population sleeping habits, factors relevant to ITN effectiveness.

Methods: Entomological 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.

Findings: Between 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.

Conclusions: Peak 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.

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Figures

Figure 1
Figure 1
Biting times of potential vector Anopheles mosquitoes during the different seasons. Top three panels show summer and winter of 1998 and spring 1999, and bottom panel shows all three catching periods combined. Dab: Dabhine, Myo: Myothugyi.
Figure 2
Figure 2
Numbers of Anopheles mosquitoes caught per person per night in Dabhine and Myothugyi during three seasons. Upper panel.
Figure 3
Figure 3
The relationship between the incidence of falciparum malaria and potential vector Anopheles mosquitoes caught on human bite catches.
Figure 4
Figure 4
Comparison of sleeping behaviour of different age-groups and biting times of Anopheles mosquitoes. The biting time data are based on 2024 human bite catches in 3 seasons.
See this image and copyright information in PMC

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