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Combining fungal biopesticides and insecticide-treated bednets to enhance malaria control.

Hancock PA - PLoS Comput. Biol. (2009)

Bottom Line: To quantify this effect, an analytically tractable gonotrophic cycle model of mosquito-malaria interactions is developed that unites existing continuous and discrete feeding cycle approaches.The effect of the combined interventions on the equilibrium EIR was at least as strong as the multiplicative effect of both interventions.Fungal biopesticide application was found to be most effective when ITN coverage was high, producing significant reductions in equilibrium prevalence for low levels of biopesticide coverage.

View Article: PubMed Central - PubMed

Affiliation: Centre for Population Biology, Imperial College London, Silwood Park Campus, Ascot, Berkshire, United Kingdom. p.hancock@imperial.ac.uk

ABSTRACT
In developing strategies to control malaria vectors, there is increased interest in biological methods that do not cause instant vector mortality, but have sublethal and lethal effects at different ages and stages in the mosquito life cycle. These techniques, particularly if integrated with other vector control interventions, may produce substantial reductions in malaria transmission due to the total effect of alterations to multiple life history parameters at relevant points in the life-cycle and transmission-cycle of the vector. To quantify this effect, an analytically tractable gonotrophic cycle model of mosquito-malaria interactions is developed that unites existing continuous and discrete feeding cycle approaches. As a case study, the combined use of fungal biopesticides and insecticide treated bednets (ITNs) is considered. Low values of the equilibrium EIR and human prevalence were obtained when fungal biopesticides and ITNs were combined, even for scenarios where each intervention acting alone had relatively little impact. The effect of the combined interventions on the equilibrium EIR was at least as strong as the multiplicative effect of both interventions. For scenarios representing difficult conditions for malaria control, due to high transmission intensity and widespread insecticide resistance, the effect of the combined interventions on the equilibrium EIR was greater than the multiplicative effect, as a result of synergistic interactions between the interventions. Fungal biopesticide application was found to be most effective when ITN coverage was high, producing significant reductions in equilibrium prevalence for low levels of biopesticide coverage. By incorporating biological mechanisms relevant to vectorial capacity, continuous-time vector population models can increase their applicability to integrated vector management.

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Equilibrium daily EIR and prevalence when the ITN intervention is applied in the absence of the biopesticide.Equilibrium daily EIR (solid lines) and equilibrium human prevalence (dashed lines) as a function of ITN coverage (). Lines labelled 1 correspond to the ITN intervention parameters in Table 1, and lines labelled 2 correspond to the case where the ITN intervention has no effect on mosquito mortality (other ITN intervention parameters are as in Table 1).
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pcbi-1000525-g003: Equilibrium daily EIR and prevalence when the ITN intervention is applied in the absence of the biopesticide.Equilibrium daily EIR (solid lines) and equilibrium human prevalence (dashed lines) as a function of ITN coverage (). Lines labelled 1 correspond to the ITN intervention parameters in Table 1, and lines labelled 2 correspond to the case where the ITN intervention has no effect on mosquito mortality (other ITN intervention parameters are as in Table 1).

Mentions: The ITN intervention corresponds to a limiting case of the model in which the fungal infection rate F is zero. For this case, the dynamic system is much simpler, requiring only equations (S1.1)–(S1.17), and solution of the equilibrium EIR is much simpler, given by equations (S1.18)–(S1.27). The ITN intervention produces a rapid decline in the equilibrium EIR as the ITN coverage () increases, but does not have a strong impact on the equilibrium malaria prevalence in humans until the level of ITN coverage is moderate to high (Figure 3). These patterns are similar to those produced by [31],[45]. Figure 3 also shows the case where the ITN intervention has no effect on mosquito mortality, and thus affects only the blood feeding rates fF and f. This may represent widespread insecticide resistance in the mosquito population.


Combining fungal biopesticides and insecticide-treated bednets to enhance malaria control.

Hancock PA - PLoS Comput. Biol. (2009)

Equilibrium daily EIR and prevalence when the ITN intervention is applied in the absence of the biopesticide.Equilibrium daily EIR (solid lines) and equilibrium human prevalence (dashed lines) as a function of ITN coverage (). Lines labelled 1 correspond to the ITN intervention parameters in Table 1, and lines labelled 2 correspond to the case where the ITN intervention has no effect on mosquito mortality (other ITN intervention parameters are as in Table 1).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2742557&req=5

pcbi-1000525-g003: Equilibrium daily EIR and prevalence when the ITN intervention is applied in the absence of the biopesticide.Equilibrium daily EIR (solid lines) and equilibrium human prevalence (dashed lines) as a function of ITN coverage (). Lines labelled 1 correspond to the ITN intervention parameters in Table 1, and lines labelled 2 correspond to the case where the ITN intervention has no effect on mosquito mortality (other ITN intervention parameters are as in Table 1).
Mentions: The ITN intervention corresponds to a limiting case of the model in which the fungal infection rate F is zero. For this case, the dynamic system is much simpler, requiring only equations (S1.1)–(S1.17), and solution of the equilibrium EIR is much simpler, given by equations (S1.18)–(S1.27). The ITN intervention produces a rapid decline in the equilibrium EIR as the ITN coverage () increases, but does not have a strong impact on the equilibrium malaria prevalence in humans until the level of ITN coverage is moderate to high (Figure 3). These patterns are similar to those produced by [31],[45]. Figure 3 also shows the case where the ITN intervention has no effect on mosquito mortality, and thus affects only the blood feeding rates fF and f. This may represent widespread insecticide resistance in the mosquito population.

Bottom Line: To quantify this effect, an analytically tractable gonotrophic cycle model of mosquito-malaria interactions is developed that unites existing continuous and discrete feeding cycle approaches.The effect of the combined interventions on the equilibrium EIR was at least as strong as the multiplicative effect of both interventions.Fungal biopesticide application was found to be most effective when ITN coverage was high, producing significant reductions in equilibrium prevalence for low levels of biopesticide coverage.

View Article: PubMed Central - PubMed

Affiliation: Centre for Population Biology, Imperial College London, Silwood Park Campus, Ascot, Berkshire, United Kingdom. p.hancock@imperial.ac.uk

ABSTRACT
In developing strategies to control malaria vectors, there is increased interest in biological methods that do not cause instant vector mortality, but have sublethal and lethal effects at different ages and stages in the mosquito life cycle. These techniques, particularly if integrated with other vector control interventions, may produce substantial reductions in malaria transmission due to the total effect of alterations to multiple life history parameters at relevant points in the life-cycle and transmission-cycle of the vector. To quantify this effect, an analytically tractable gonotrophic cycle model of mosquito-malaria interactions is developed that unites existing continuous and discrete feeding cycle approaches. As a case study, the combined use of fungal biopesticides and insecticide treated bednets (ITNs) is considered. Low values of the equilibrium EIR and human prevalence were obtained when fungal biopesticides and ITNs were combined, even for scenarios where each intervention acting alone had relatively little impact. The effect of the combined interventions on the equilibrium EIR was at least as strong as the multiplicative effect of both interventions. For scenarios representing difficult conditions for malaria control, due to high transmission intensity and widespread insecticide resistance, the effect of the combined interventions on the equilibrium EIR was greater than the multiplicative effect, as a result of synergistic interactions between the interventions. Fungal biopesticide application was found to be most effective when ITN coverage was high, producing significant reductions in equilibrium prevalence for low levels of biopesticide coverage. By incorporating biological mechanisms relevant to vectorial capacity, continuous-time vector population models can increase their applicability to integrated vector management.

Show MeSH
Related in: MedlinePlus