Interactions between a fungal entomopathogen and malaria parasites within a mosquito vector.

Rebecca L Heinig,Matthew B Thomas

doi:10.1186/s12936-014-0526-x

Abstract

BackgroundMosquitoes are becoming increasingly resistant to the chemical insecticides currently available for malaria vector control, spurring interest in alternative management tools. One promising technology is the use of fungal entomopathogens. Fungi have been shown to impact the potential for mosquitoes to transmit malaria by reducing mosquito longevity and altering behaviour associated with flight and host location. Additionally, fungi could impact the development of malaria parasites within the mosquito via competition for resources or effects on the mosquito immune system. This study evaluated whether co-infection or superinfection with the fungal entomopathogen Beauveria bassiana affected malaria infection progress in Anopheles stephensi mosquitoes.MethodsThe study used two parasite species to examine possible effects of fungal infection at different parasite development stages. First, the rodent malaria model Plasmodium yoelii was used to explore interactions at the oocyst stage. Plasmodium yoelii produces high oocyst densities in infected mosquitoes and thus was expected to maximize host immunological and resource demands. Second, fungal interactions with mature sporozoites were evaluated by infecting mosquitoes with the human malaria species Plasmodium falciparum, which is highly efficient at invading mosquito salivary glands.ResultsWith P. yoelii, there was no evidence that fungal co-infection (on the same day as the blood meal) or superinfection (during a subsequent gonotrophic cycle after parasite infection) affected the proportion of mosquitoes with oocysts, the number of oocysts per infected mosquito or the number of sporozoites per oocyst. Similarly, for P. falciparum, there was no evidence that fungal infection affected sporozoite prevalence. Furthermore, there was no impact of infection with either malaria species on fungal virulence as measured by mosquito survival time.ConclusionsThese results suggest that the impact of fungus on malaria control potential is limited to the well-established effects on mosquito survival and transmission behaviour. Direct or indirect interactions between fungus and malaria parasites within mosquitoes appear to have little additional influence.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-014-0526-x) contains supplementary material, which is available to authorized users.

Highlights

Mosquitoes are becoming increasingly resistant to the chemical insecticides currently available for malaria vector control, spurring interest in alternative management tools
This study explored whether co- or superinfection with a candidate strain of the fungal entomopathogen B. bassiana affected a number of malaria infection parameters
Pupae were placed into cages for emergence, and adults were given a 10% glucose solution supplemented with 0.05% para-aminobenzoic acid (PABA) to enhance P. yoelii oocyst infection rate [57]

Summary

Introduction

Mosquitoes are becoming increasingly resistant to the chemical insecticides currently available for malaria vector control, spurring interest in alternative management tools. Malaria vector control programmes are currently being threatened by increasing insecticide resistance in adult mosquito populations [1,2,3,4]. This has spurred interest in the development of alternative management tools, including the use of entomopathogenic fungi [5,6,7,8]. Fungal biopesticides are relatively slow-acting, taking up to a week or more to kill exposed mosquitoes [5,13] This slower action can still be sufficient to block malaria transmission, since mosquitoes do not become infective until the end of the malarial extrinsic incubation period

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Results

Conclusion