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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 effect of varying the period of biopesticide exposure in a given gonotrophic cycle.Equilibrium daily EIR and equilibrium human prevalence as a function of the daily probability of fungal infection during the period of biopesticide exposure (CE) for three values of the mean time to death from fungal infection (): A–B. , C–D. , E–F. . Lines represent biopesticide exposure periods (see text) corresponding to  (solid lines),  (dashed lines) and  (dot-dashed lines).
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pcbi-1000525-g005: The effect of varying the period of biopesticide exposure in a given gonotrophic cycle.Equilibrium daily EIR and equilibrium human prevalence as a function of the daily probability of fungal infection during the period of biopesticide exposure (CE) for three values of the mean time to death from fungal infection (): A–B. , C–D. , E–F. . Lines represent biopesticide exposure periods (see text) corresponding to (solid lines), (dashed lines) and (dot-dashed lines).

Mentions: The equilibrium daily EIR is marginally higher if mosquitoes are exposed to fungal infection risk for half of the non-host-seeking stage () in comparison to exposure for the full stage duration () (Figure 5A, C, E). However, if mosquitoes are only exposed to fungal infection risk when they are host-seeking (), the equilibrium EIR is considerably higher. The corresponding estimate of the equilibrium malaria prevalence in humans varies more between the three exposure periods than the equilibrium EIR (Figure 5B, D, F), because it is sensitive to changes in EIR at low EIR values. The effect of varying the period of biopesticide exposure on prevalence is greater for more virulent biopesticides, which benefit more from the very low transmission levels achieved for longer duration of exposure to fungal infection risk (Figure 5A, B). Similar to [21], if mosquitoes are always exposed to fungal infection risk, there is a threshold level of the daily probability of fungal infection above which additional reductions in equilibrium EIR and prevalence are marginal. This is not the case if mosquitoes are only exposed to fungal infection risk when they are host-seeking, where prevalence continues to decline steadily as the daily probability of fungal infection is increased to high values (Figure 5).


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

Hancock PA - PLoS Comput. Biol. (2009)

The effect of varying the period of biopesticide exposure in a given gonotrophic cycle.Equilibrium daily EIR and equilibrium human prevalence as a function of the daily probability of fungal infection during the period of biopesticide exposure (CE) for three values of the mean time to death from fungal infection (): A–B. , C–D. , E–F. . Lines represent biopesticide exposure periods (see text) corresponding to  (solid lines),  (dashed lines) and  (dot-dashed lines).
© Copyright Policy
Related In: Results  -  Collection

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

pcbi-1000525-g005: The effect of varying the period of biopesticide exposure in a given gonotrophic cycle.Equilibrium daily EIR and equilibrium human prevalence as a function of the daily probability of fungal infection during the period of biopesticide exposure (CE) for three values of the mean time to death from fungal infection (): A–B. , C–D. , E–F. . Lines represent biopesticide exposure periods (see text) corresponding to (solid lines), (dashed lines) and (dot-dashed lines).
Mentions: The equilibrium daily EIR is marginally higher if mosquitoes are exposed to fungal infection risk for half of the non-host-seeking stage () in comparison to exposure for the full stage duration () (Figure 5A, C, E). However, if mosquitoes are only exposed to fungal infection risk when they are host-seeking (), the equilibrium EIR is considerably higher. The corresponding estimate of the equilibrium malaria prevalence in humans varies more between the three exposure periods than the equilibrium EIR (Figure 5B, D, F), because it is sensitive to changes in EIR at low EIR values. The effect of varying the period of biopesticide exposure on prevalence is greater for more virulent biopesticides, which benefit more from the very low transmission levels achieved for longer duration of exposure to fungal infection risk (Figure 5A, B). Similar to [21], if mosquitoes are always exposed to fungal infection risk, there is a threshold level of the daily probability of fungal infection above which additional reductions in equilibrium EIR and prevalence are marginal. This is not the case if mosquitoes are only exposed to fungal infection risk when they are host-seeking, where prevalence continues to decline steadily as the daily probability of fungal infection is increased to high values (Figure 5).

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