Background
Methods
Study design
Study areas
Sample size
Selection of intervention and control clusters/villages
Selection of households for measuring sand fly densities
Cluster allocation to intervention arms
Study arms and interventions
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IRS: in Bangladesh this was done using deltamethrin (K-Otrine 5%, Aventis Bayer company, target concentration 20 mg active ingredient per square metre); in India we used DDT 5% (target concentration 1 g/m2, Hindustan Insecticide Limited); and in Nepal we used alpha-cypermethrine (target concentration 0.025 gm/m2, Gharda Chemical LTD, Mumbai, India). IRS was carried out by the district vector staff, except for Bangladesh where the research team themselves had to do it in the absence of a vector control programme. Prior to the day of spraying, the head of household was informed of the procedure and date of IRS and was asked to sign a consent form. On the day of spraying, family members removed food, clothing, bed linen and animals before spraying. A spray field worker applied the insecticide to the interior (in Bangladesh also to the exterior) walls of the house and cattle sheds, up to 6 ft high, targeting the cracks and crevices. Quality control was done by the research team. Every household of the entire village/cluster was treated. Heads of household were told not to re-plaster their walls. The insecticides used in the study (as well as in routine vector control programmes) are efficacious against sand fly vectors (see the bioassay results below).
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LLIN: PermaNet® nets (Vestergaard-Frandsen Company, Lausanne, Switzerland) with small mesh (156 holes/in2), polyester, resin coating containing deltamethrin (55 mg/m2) were distributed in all households of this study arm during the week 0 after the first survey in order to cover all household members based on reported sleeping arrangements. Two net sizes (160 × 180 × 150 cm and 100 × 180 × 150 cm) were used depending upon household members and sleeping arrangements.
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EVM: Trained community mobilizers met with each family to discuss the typical resting and breeding sites in and around houses and the appropriate ways to reducing them. In Nepal and India wall plastering with a lime/mud mixture was promoted, the lime being provided free of charge to the households. In Bangladesh plastering was done with mud only. The heads of household did the wall plastering themselves as it is a common practice. In Bangladesh a token incentive was provided to the children and housewives in order to encourage their participation. After the initial plastering activities, the community mobilizers conducted weekly home visits and meetings to promote the continuing filling of cracks and crevices in houses and cattle sheds [15].
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Control: Control clusters were similar in all ways to the intervention clusters; no specific vector control intervention was carried out.
Entomological monitoring
Bio-assays
Statistical analysis
Results
Pooled analysis
LLIN | IRS | EVM | Control |
P-value test of difference | |||||||||||
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CI 95% | CI 95% | CI 95% | CI 95% | LLIN versus Control | IRS versus Control | EVM versus Control | |||||||||
Survey*
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Mean
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Lower
|
Upper
|
Mean
|
Lower
|
Upper
|
Mean
|
Lower
|
Upper
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Mean
|
Lower
|
Upper
| |||
Baseline | 9.92 | 7.28 | 13.53 | 12.32 | 9.54 | 15.92 | 13.21 | 9.94 | 17.55 | 9.41 | 6.97 | 12.71 | 0.798 | 0.184 | 0.108 |
5 months follow-up | 8.32 | 5.56 | 12.45 | 6.14 | 4.00 | 10.47 | 10.39 | 7.56 | 14.29 | 12.15 | 8.68 | 17.00 | 0.160 | 0.035 | 0.503 |
LLIN | IRS | EVM | ||
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Model | Parameter | Coefficient (P-value) |
P-value |
P-value |
Simple (crude estimates) | Intervention effect† | -0.43 (0.042) | -0.95 (<0.001) | -0.49 (0.024) |
Reduction in counts (95% CI)‡ | -4.34 (-8.57,-0.10) 43.7% | -8.92 (-13.20,-4.64) 72.4% | -5.55 (-10.57,-0.53) 42.0% | |
Full | Intervention effect | -0.42 (0.044) | -0.94 (0.001) | -0.49 (0.025) |
Type of wall | -0.02 (0.881) | -0.17 (0.260) | 0.01 (0.925) | |
Type of dwelling | 0.00 (0.996) | 0.27 (0.032) | 0.26 (0.020) | |
Type of dwelling | Intervention effect | -0.43 (0.042) | -0.95 (<0.001) | -0.49 (0.024) |
Type of dwelling | -0.01 (0.970) | 0.25 (0.043) | 0.26 (0.021) | |
Type of wall | Intervention effect | -0.43 (0.044) | -0.94 (<0.001) | -0.49 (0.025) |
Type of wall | -0.02 (0.876) | -0.16 (0.289) | 0.02 (0.875) |
Site specific analysis
Site | LLIN† | IRS† | EVM† |
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Nepal 1 (n = 120) | -3.80 (-14.7, 7.1) 22% | -10.7 (-26.7, 5.3) 53% | -10.6 (-22.3, 1.2) 51% |
Nepal 2 (n = 240) | -2.11 (-8.4, 4.2) 16% | -8.5 (-16.0, -0.9) 52% | -0.6 (-10.7, 9.5) 4% |
Bangladesh (n = 240) | -8.2 (-13.8, -2.7) 68% | -10.3 (-13.8, -6.8) 94% | -0.8 (-5.4, 3.8) 9% |
India (n = 240) | -2.9 (-3.7, -2.1) 298% | -7.1 (-9.5, -4.7) 124% | -12.0 (-15.8, -8.1) 108% |
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IRS resulted in significant sand fly reductions in all sites independent of type of walls or dwelling or type of insecticide (DDT or pyrethroids).
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LLINs had a significant negative effect on sand fly densities in India and Bangladesh, but not in the two Nepal sites (see the discussion section)
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EVM using mud for wall plastering in Bangladesh was not effective; EVM using lime plastering significantly reduced the sand fly densities in India and Nepal (Sarlahi and Sunsari districts) but not in the other Nepal site (Morang district; see discussion)