Abstract

BackgroundMalaria is one of the most lethal infectious diseases in tropical and subtropical areas of the world. Paratransgenesis using symbiotic bacteria offers a sustainable and environmentally friendly strategy to combat this disease. In the study reported here, we evaluated the disruption of malaria transmission in the Anopheles stephensi-Plasmodium berghei assemblage using the wild-type (WT) and three modified strains of the insect gut bacterium, Enterobacter cloacae.MethodsThe assay was carried out using the E. cloacae dissolvens WT and three engineered strains (expressing green fluorescent protein-defensin (GFP-D), scorpine-HasA (S-HasA) and HasA only, respectively). Cotton wool soaked in a solution of 5% (wt/vol) fructose + red dye (1/50 ml) laced with one of the bacterial strains (1 × 109cells/ml) was placed overnight in cages containing female An. stephensi mosquitoes (age: 3–5 days). Each group of sugar-fed mosquitoes was then starved for 4–6 h, following which time they were allowed to blood-feed on P. berghei–infected mice for 20 min in the dark at 17–20 °C. The blood-fed mosquitoes were kept at 19 ± 1 °C and 80 ± 5% relative humidity, and parasite infection was measured by midgut dissection and oocyst counting 10 days post-infection (dpi).ResultsExposure to both WT and genetically modified E. cloacae dissolvens strains significantly (P < 0.0001) disrupted P. berghei development in the midgut of An. stephensi, in comparison with the control group. The mean parasite inhibition of E. cloacaeWT, E. cloacaeHasA, E. cloacaeS−HasA and E. cloacaeGFP−D was measured as 72, 86, 92.5 and 92.8 respectively.ConclusionsThe WT and modified strains of E. cloacae have the potential to abolish oocyst development by providing a physical barrier or through the excretion of intrinsic effector molecules. These findings reinforce the case for the use of either WT or genetically modified strains of E. cloacae bacteria as a powerful tool to combat malaria.Graphical

Highlights

  • Malaria is one of the most lethal infectious diseases in tropical and subtropical areas of the world

  • The Plasmodium parasite is the causative agent of malaria, and the female Anopheles mosquito is the vector of the Dehghan et al Parasites & Vectors (2022) 15:63 disease

  • Programs aimed at controlling A. stephensi populations and limiting the ability of these mosquitoes to transmit Plasmodium have the potential to reduce the burden of malaria disease [6]

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Summary

Introduction

Malaria is one of the most lethal infectious diseases in tropical and subtropical areas of the world. Transmission-blocking strategies (TBS) have recently been proposed as a potential means of malaria control, with an increased emphasis on inhibiting the development of the Plasmodium parasite in the vector mosquito [16,17,18,19]. The last method consists of genetically manipulating Anopheles mosquitoes to render them refractory to Plasmodium parasite development. This is accomplished using anti-plasmodium molecules (transgenesis) [20], naturally refractory mosquitoes [21], artificial gene-drive mechanisms [22, 23] and/or micro-symbionts genetically modified by effector molecules that are reintroduced into the wild mosquito population (paratransgenesis) [6, 12, 24, 25]

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