New methods of biocontrol for malaria
Malaria is a major contributor to the global disease burden, and disproportionately affects low-income countries with climates suitable for transmission. Vector control strategies have proven effective in reducing malaria transmission and prevalence, and are a key element of current malaria control initiatives. Indoor residual spraying and insecticide-treated bednets (ITNs) have been and remain the dominant methods of controlling malaria vectors, but problems of public health and insecticide resistance associated with chemical insecticides have increased interest in alternate methods, including novel biological methods. Because the incubation period of the malaria parasite is relatively long in comparison to the average adult mosquito lifespan, biological methods of vector control that have sublethal and lethal effects at different points in the mosquito life cycle may substantially reduce the potential for malaria transmission.
Biopesticides containing a fungus that is pathogenic to mosquitoes may be an effective means of reducing malaria transmission, particularly if used in combination with insecticide-treated ITNs. Results of a new study show that incorporating this novel vector control technique into existing vector management programmes may substantially reduce malaria transmission rates and help manage insecticide resistance. Using data from laboratory and field studies, the model estimates the impact of different vector control interventions on the mosquito life cycle and the average numbers of mosquitoes that survive to transmit malaria. The results indicate that in order to successfully control malaria transmission, single intervention strategies must be widely used across the community, whether the strategy involves fungal biopesticides or ITNs. If used in combination, the model shows that the interventions can interact to produce greater-than-expected reductions in malaria transmission rates.
This outcome is achieved because the presence of ITNs can increase mosquito exposure to biopesticide-sprayed surfaces. Efficient combinations of interventions may allow each to be used at lower levels, and slow the development of resistance in the mosquito population. The results suggest that combining fungal biopesticides and ITNs may be an efficient and effective strategy for malaria vector control. Malaria is a major contributor to the global disease burden, and disproportionately affects low income countries with climates suitable for transmission. Mosquito control relies heavily on chemical insecticides, but growing problems of insecticide resistance have led to increased interest in novel methods, including biocontrol. The Global Strategy for Integrated Vector Management, developed by the World Health Organisation, encourages the use of multiple vector control technologies in combination. This research has used computer modelling to identify ways in which interventions can be combined to maximise the impact on malaria transmission, given the resources available.
Combining Fungal Biopesticides and Insecticide-Treated Bednets to Enhance Malaria Control. 2009 PLoS Comput Biol 5(10): e1000525 doi:10.1371/journal.pcbi.1000525
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 mosquitomalaria 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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Tags: Biology, Biotechnology, Environment, Malaria, Medicine, Microbiology, Parasitology, Science
