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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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Related in: MedlinePlus

Comparing the impact of the combined interventions to the multiplicative effect of both interventions.The amount by which the equilibrium prevalence deviates from the multiplicative effect of both interventions () as a function of the ITN coverage (). Points represent different ITN intervention parameters, including the parameters given in Table 1 (open circles) and the case where the ITN intervention does not affect mosquito mortality (crosses). All combinations of mean times to death from fungal infection () of , and values of the daily probability of fungal infection during the period of biopesticide exposure (CE) of CE = 0.2, 0.4, 0.6 and 0.8, are shown. Panels show different levels of transmission intensity: A. Annual EIR = 47.8, B. Annual EIR = 412.
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pcbi-1000525-g007: Comparing the impact of the combined interventions to the multiplicative effect of both interventions.The amount by which the equilibrium prevalence deviates from the multiplicative effect of both interventions () as a function of the ITN coverage (). Points represent different ITN intervention parameters, including the parameters given in Table 1 (open circles) and the case where the ITN intervention does not affect mosquito mortality (crosses). All combinations of mean times to death from fungal infection () of , and values of the daily probability of fungal infection during the period of biopesticide exposure (CE) of CE = 0.2, 0.4, 0.6 and 0.8, are shown. Panels show different levels of transmission intensity: A. Annual EIR = 47.8, B. Annual EIR = 412.

Mentions: Low values of equilibrium prevalence are not obtained by the fungal biopesticide intervention alone, or by the ITN intervention alone unless ITN coverage is high (Figure 6A). When both interventions are used in combination, low prevalence is obtained with moderate coverage of each intervention. The proportional reduction in equilibrium EIR obtained by the combined interventions found to be very close to the multiplicative effect of both interventions, or the product of the proportional reductions given by each intervention acting alone. The difference between the equilibrium prevalence obtained from the combining the two interventions, , and the prevalence corresponding to the multiplicative effect of the two interventions on the equilibrium EIR, denoted , is calculated as . As is small in this case (Figure 7A, open circles), there is negligible redundancy in combining both interventions, and also negligible synergistic effects, or no increase in the impact of one intervention on malaria transmission due to the presence of the other intervention.


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

Hancock PA - PLoS Comput. Biol. (2009)

Comparing the impact of the combined interventions to the multiplicative effect of both interventions.The amount by which the equilibrium prevalence deviates from the multiplicative effect of both interventions () as a function of the ITN coverage (). Points represent different ITN intervention parameters, including the parameters given in Table 1 (open circles) and the case where the ITN intervention does not affect mosquito mortality (crosses). All combinations of mean times to death from fungal infection () of , and values of the daily probability of fungal infection during the period of biopesticide exposure (CE) of CE = 0.2, 0.4, 0.6 and 0.8, are shown. Panels show different levels of transmission intensity: A. Annual EIR = 47.8, B. Annual EIR = 412.
© Copyright Policy
Related In: Results  -  Collection

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

pcbi-1000525-g007: Comparing the impact of the combined interventions to the multiplicative effect of both interventions.The amount by which the equilibrium prevalence deviates from the multiplicative effect of both interventions () as a function of the ITN coverage (). Points represent different ITN intervention parameters, including the parameters given in Table 1 (open circles) and the case where the ITN intervention does not affect mosquito mortality (crosses). All combinations of mean times to death from fungal infection () of , and values of the daily probability of fungal infection during the period of biopesticide exposure (CE) of CE = 0.2, 0.4, 0.6 and 0.8, are shown. Panels show different levels of transmission intensity: A. Annual EIR = 47.8, B. Annual EIR = 412.
Mentions: Low values of equilibrium prevalence are not obtained by the fungal biopesticide intervention alone, or by the ITN intervention alone unless ITN coverage is high (Figure 6A). When both interventions are used in combination, low prevalence is obtained with moderate coverage of each intervention. The proportional reduction in equilibrium EIR obtained by the combined interventions found to be very close to the multiplicative effect of both interventions, or the product of the proportional reductions given by each intervention acting alone. The difference between the equilibrium prevalence obtained from the combining the two interventions, , and the prevalence corresponding to the multiplicative effect of the two interventions on the equilibrium EIR, denoted , is calculated as . As is small in this case (Figure 7A, open circles), there is negligible redundancy in combining both interventions, and also negligible synergistic effects, or no increase in the impact of one intervention on malaria transmission due to the presence of the other intervention.

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