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, 4 (9), e6921

Modeling the Effects of Integrating Larval Habitat Source Reduction and Insecticide Treated Nets for Malaria Control


Modeling the Effects of Integrating Larval Habitat Source Reduction and Insecticide Treated Nets for Malaria Control

Laith Yakob et al. PLoS One.

Erratum in

  • PLoS One. 2009; 4(11). doi: 10.1371/annotation/9d928eac-d6d9-4e75-bb1a-3a25c930c77f


Integrated vector management for malaria control has received a lot of recent interest. Attacking multiple points in the transmission cycle is hoped to act synergistically and improve upon current single-tool interventions based on the use of insecticide-treated bed nets (ITNs). In the present study, we theoretically examined the application of larval habitat source reduction with ITNs in reducing malaria transmission. We selected this type of environmental management to complement ITNs because of a potential secondary mode of action that both control strategies share. In addition to increasing vector mortality, ITNs reduce the rate at which female mosquitoes locate human hosts for blood feeding, thereby extending their gonotrophic cycle. Similarly, while reducing adult vector emergence and abundance, source reduction of larval habitats may prolong the cycle duration by extending delays in locating oviposition sites. We found, however, that source reduction of larval habitats only operates through this secondary mode of action when habitat density is below a critical threshold. Hence, we illustrate how this strategy becomes increasingly effective when larval habitats are limited. We also demonstrate that habitat source reduction is better suited to human populations of higher density and in the presence of insecticide resistance or when the insecticidal properties of ITNs are depleted.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.


Figure 1
Figure 1. Resource availability influences the a) mosquito gonotrophic cycle, ‘G’, and b) R0 of malaria.
Mosquito resources consist of human blood meals and larval habitats. Availability of the unvaried resource was maintained at 1,000 per sq Km. “+” denotes the point at which the delay in locating oviposition sites equals the embryogenesis duration, and “++” denotes the point at which the gonotrophic cycle duration equals the extrinsic incubation period of malaria. The gray area highlights the region of R0<1, where malaria fails to persist. Results for mosquitoes with a searching ability of 1,000 sq m per day are shown.
Figure 2
Figure 2. R0 of malaria relative to the coverage and mosquito killing efficiency (ω) of ITNs.
Results are shown for when human density is a) ‘Low’ (100 per sq Km), b) ‘Medium’ (333 per sq Km) and c) ‘High’ (1,000 per sq Km) and for mosquitoes that search 1,000 sq m per day. Larval habitat density is maintained at 1,000 per sq Km.
Figure 3
Figure 3. Influence of mosquito search ability on critical thresholds for the persistence of malaria.
Letting R0 and Rc respectively denote the reproductive number in the absence and presence of control, the three parameter spaces are represented thusly: red (Rc>R0, worse than no control), white (Rc<R0, suppression but not elimination) and gray (Rc<1, elimination of malaria transmission). Results are shown for a range of resource-locating abilities of the mosquito: 1,000 sq m per day (in a, b and c), 2,000 sq m per day (in d, e and f) and 3,000 sq m per day (in g, h and i). Human density values used in the simulation were: ‘Low’ (100 per sq Km in a, d and g), ‘Medium’ (333 per sq Km in b, e and h) and ‘High’ (1,000 per sq Km in c, f and i). Larval habitat density is maintained at 1,000 per sq Km.
Figure 4
Figure 4. ITNs and habitat source reduction in the integrated control of malaria.
The colors correspond to the basic reproductive number of malaria (R0) as highlighted in the key (the parameter space for local malaria elimination, R0<1, is black). The values in white font at the top-right corner of the plots indicate the killing efficacy of the ITNs: 0.5 (a, b and c); 0.25 (d, e and f); and 0.0 (g, h and i). Three human densities are used: ‘Low’ (100 per sq Km) (a, d and g), ‘Medium’ (333 per sq Km) (b, e and h), and ‘High’ (1,000 per sq Km) (c, f and i). Other parameters used in the simulation are mosquito search ability 1,000 sq m per day, and larval habitat density 1,000 per sq Km.
Figure 5
Figure 5. ITNs used alone or in conjunction with environmental management (EM) for malaria control.
Parameters used in the simulation are as following: human density is ‘Low’ (100 per sq Km; a, d and g), ‘Medium’ (333 per sq Km; b, e and h), and ‘High’ (1000 per sq Km; c, f and i); larval habitat density is ‘Low’ (100 per sq Km; a, b and c), ‘Medium’ (333 per sq Km; d, e and f), and ‘High’ (1,000 per sq Km; g, h and i); mosquito search ability is 1,000 sq m per day; killing efficacy of the ITNs is 0.25; and habitat source reduction rate is 0.5.

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