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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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Comparing equilibria obtained by simulation and analytic derivation.Equilibrium daily EIR as a function of the mean time to death if the fungus is the only mortality source () for different values of the shape parameter  and other parameters as in Table 1. For  values of the equilibrium daily EIR obtained by analytic derivation (open diamonds) and simulation (black squares) are compared. Sublethal effects of fungal infection on mosquito feeding biology are not incorporated ( & ).
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pcbi-1000525-g002: Comparing equilibria obtained by simulation and analytic derivation.Equilibrium daily EIR as a function of the mean time to death if the fungus is the only mortality source () for different values of the shape parameter and other parameters as in Table 1. For values of the equilibrium daily EIR obtained by analytic derivation (open diamonds) and simulation (black squares) are compared. Sublethal effects of fungal infection on mosquito feeding biology are not incorporated ( & ).

Mentions: Expressions are derived for the equilibrium density of susceptible, exposed and infectious host-seeking mosquitoes for the limiting case in which there are no sublethal effects of fungal infection on mosquito feeding biology (, ) and the shape parameter of the fungal pathogen-induced mortality function (Text S1 and Text S2). The analytically derived equilibrium EIR agrees well with the equilibrium obtained by simulating equations (S1.1)–(S1.17) and (S2.1)–(S2.18) through time using a simulation algorithm coded in C++ (Figure 2). The simulation algorithm is used to obtain the equilibrium for the general case in which , and . The pattern in Figure 2 is similar to that produced by simpler models [21], whereby increasing the shape parameter β above 1 reduces the equilibrium malaria transmission rate.


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

Hancock PA - PLoS Comput. Biol. (2009)

Comparing equilibria obtained by simulation and analytic derivation.Equilibrium daily EIR as a function of the mean time to death if the fungus is the only mortality source () for different values of the shape parameter  and other parameters as in Table 1. For  values of the equilibrium daily EIR obtained by analytic derivation (open diamonds) and simulation (black squares) are compared. Sublethal effects of fungal infection on mosquito feeding biology are not incorporated ( & ).
© Copyright Policy
Related In: Results  -  Collection

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

pcbi-1000525-g002: Comparing equilibria obtained by simulation and analytic derivation.Equilibrium daily EIR as a function of the mean time to death if the fungus is the only mortality source () for different values of the shape parameter and other parameters as in Table 1. For values of the equilibrium daily EIR obtained by analytic derivation (open diamonds) and simulation (black squares) are compared. Sublethal effects of fungal infection on mosquito feeding biology are not incorporated ( & ).
Mentions: Expressions are derived for the equilibrium density of susceptible, exposed and infectious host-seeking mosquitoes for the limiting case in which there are no sublethal effects of fungal infection on mosquito feeding biology (, ) and the shape parameter of the fungal pathogen-induced mortality function (Text S1 and Text S2). The analytically derived equilibrium EIR agrees well with the equilibrium obtained by simulating equations (S1.1)–(S1.17) and (S2.1)–(S2.18) through time using a simulation algorithm coded in C++ (Figure 2). The simulation algorithm is used to obtain the equilibrium for the general case in which , and . The pattern in Figure 2 is similar to that produced by simpler models [21], whereby increasing the shape parameter β above 1 reduces the equilibrium malaria transmission rate.

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