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Modeling the effects of integrating larval habitat source reduction and insecticide treated nets for malaria control.

Yakob L, Yan G - PLoS ONE (2009)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Program in Public Health, University of California Irvine, Irvine, California, United States of America. lyakob@uci.edu

ABSTRACT
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.

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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.
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pone-0006921-g001: 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.

Mentions: Anopheles gambiae mosquitoes need human blood meals for egg production and larval habitats for oviposition. Therefore, human blood meals and larval habitats are considered important resources for the mosquitoes. Intuitively, as resources become more available, delays in the gonotrophic cycle (G) resulting from the finite searching ability of the mosquito (s) are reduced (all variables are defined along with their units in Table 1). Consequently, the bite rate increases, and with it, the basic reproductive number of malaria (R0). An interesting finding illustrated in Fig. 1a is that beyond a threshold, increased larval habitat density (θ) does not confer any additional reduction in the delay in the gonotrophic cycle. At this point, the duration of embryogenesis exceeds the delay in locating breeding sites . Hence, the duration of the cycle consists of the maturation time of the embryos (ε) summed with the delay in locating the blood meal (, where σ is human host density).


Modeling the effects of integrating larval habitat source reduction and insecticide treated nets for malaria control.

Yakob L, Yan G - PLoS ONE (2009)

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.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2734167&req=5

pone-0006921-g001: 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.
Mentions: Anopheles gambiae mosquitoes need human blood meals for egg production and larval habitats for oviposition. Therefore, human blood meals and larval habitats are considered important resources for the mosquitoes. Intuitively, as resources become more available, delays in the gonotrophic cycle (G) resulting from the finite searching ability of the mosquito (s) are reduced (all variables are defined along with their units in Table 1). Consequently, the bite rate increases, and with it, the basic reproductive number of malaria (R0). An interesting finding illustrated in Fig. 1a is that beyond a threshold, increased larval habitat density (θ) does not confer any additional reduction in the delay in the gonotrophic cycle. At this point, the duration of embryogenesis exceeds the delay in locating breeding sites . Hence, the duration of the cycle consists of the maturation time of the embryos (ε) summed with the delay in locating the blood meal (, where σ is human host density).

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Program in Public Health, University of California Irvine, Irvine, California, United States of America. lyakob@uci.edu

ABSTRACT
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.

Show MeSH
Related in: MedlinePlus