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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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The impact of sublethal effects of fungal infection on mosquito feeding biology.Equilibrium daily EIR as a function of the mean time to death from fungal infection () for three values of the daily probability of fungal infection (): A, C = 0.1 B, C = 0.5 C, C = 0.9. Lines represent varying sublethal effects of fungal infection on mosquito feeding biology, including no sublethal effects (solid lines), a 25% decrease in the daily probability of finding a blood meal () and a 25% increase in the duration of the non-host-seeking stage () in fungal pathogen-infected mosquitoes (dashed lines), a 50% decrease in  and a 50% increase in  (dotted lines), and a 75% decrease in  and a 75% increase in  (dot-dashed lines). Other parameters are given in Table 1.
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pcbi-1000525-g004: The impact of sublethal effects of fungal infection on mosquito feeding biology.Equilibrium daily EIR as a function of the mean time to death from fungal infection () for three values of the daily probability of fungal infection (): A, C = 0.1 B, C = 0.5 C, C = 0.9. Lines represent varying sublethal effects of fungal infection on mosquito feeding biology, including no sublethal effects (solid lines), a 25% decrease in the daily probability of finding a blood meal () and a 25% increase in the duration of the non-host-seeking stage () in fungal pathogen-infected mosquitoes (dashed lines), a 50% decrease in and a 50% increase in (dotted lines), and a 75% decrease in and a 75% increase in (dot-dashed lines). Other parameters are given in Table 1.

Mentions: Fungal infection can substantially reduce mosquito blood-feeding activity [26]. Here, two possible effects of fungal infection on mosquito blood-feeding biology are considered, including a reduction in the blood-feeding rate in host-seeking mosquitoes, , and an increase in the duration of the non-host-seeking stage, (Table 1). Even when these effects act simultaneously, they have less potential to produce very low equilibrium EIR than decreasing the average time to death from fungal infection, (Figure 4). The strongest sublethal effects shown in Figure 4 represent more than a four fold increase in the average gonotrophic cycle length in fungal pathogen-infected mosquitoes, . For moderate to high daily probability of fungal infection, this has a similar effect to a 25% reduction in the average time to death from fungal infection (Figure 4B and C). When the daily probability of fungal infection is low, reductions in the equilibrium EIR obtained by either increasing the fungal pathogen virulence (by reducing ) or increasing the sublethal effects are considerably less, and the impact of strong sublethal effects on the EIR is of similar magnitude to that produced by strong reductions in (Figure 4A).


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

Hancock PA - PLoS Comput. Biol. (2009)

The impact of sublethal effects of fungal infection on mosquito feeding biology.Equilibrium daily EIR as a function of the mean time to death from fungal infection () for three values of the daily probability of fungal infection (): A, C = 0.1 B, C = 0.5 C, C = 0.9. Lines represent varying sublethal effects of fungal infection on mosquito feeding biology, including no sublethal effects (solid lines), a 25% decrease in the daily probability of finding a blood meal () and a 25% increase in the duration of the non-host-seeking stage () in fungal pathogen-infected mosquitoes (dashed lines), a 50% decrease in  and a 50% increase in  (dotted lines), and a 75% decrease in  and a 75% increase in  (dot-dashed lines). Other parameters are given in Table 1.
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Related In: Results  -  Collection

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

pcbi-1000525-g004: The impact of sublethal effects of fungal infection on mosquito feeding biology.Equilibrium daily EIR as a function of the mean time to death from fungal infection () for three values of the daily probability of fungal infection (): A, C = 0.1 B, C = 0.5 C, C = 0.9. Lines represent varying sublethal effects of fungal infection on mosquito feeding biology, including no sublethal effects (solid lines), a 25% decrease in the daily probability of finding a blood meal () and a 25% increase in the duration of the non-host-seeking stage () in fungal pathogen-infected mosquitoes (dashed lines), a 50% decrease in and a 50% increase in (dotted lines), and a 75% decrease in and a 75% increase in (dot-dashed lines). Other parameters are given in Table 1.
Mentions: Fungal infection can substantially reduce mosquito blood-feeding activity [26]. Here, two possible effects of fungal infection on mosquito blood-feeding biology are considered, including a reduction in the blood-feeding rate in host-seeking mosquitoes, , and an increase in the duration of the non-host-seeking stage, (Table 1). Even when these effects act simultaneously, they have less potential to produce very low equilibrium EIR than decreasing the average time to death from fungal infection, (Figure 4). The strongest sublethal effects shown in Figure 4 represent more than a four fold increase in the average gonotrophic cycle length in fungal pathogen-infected mosquitoes, . For moderate to high daily probability of fungal infection, this has a similar effect to a 25% reduction in the average time to death from fungal infection (Figure 4B and C). When the daily probability of fungal infection is low, reductions in the equilibrium EIR obtained by either increasing the fungal pathogen virulence (by reducing ) or increasing the sublethal effects are considerably less, and the impact of strong sublethal effects on the EIR is of similar magnitude to that produced by strong reductions in (Figure 4A).

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