# Evaluating paratransgenesis using engineered symbiotic bacteria for Plasmodium inhibition in mosquito vectors: A systematic review

## TL;DR

This review evaluates using genetically modified bacteria in mosquitoes to block malaria parasite transmission, showing promising results but highlighting challenges for real-world use.

## Contribution

A systematic review of paratransgenesis as a novel malaria control strategy using engineered symbiotic microbes to inhibit Plasmodium development in mosquitoes.

## Key findings

- Engineered microbes like Asaia and Serratia effectively colonized mosquito midguts and inhibited Plasmodium parasites.
- Scorpine was the most effective effector, achieving up to 97.8% inhibition of P. falciparum oocysts.
- Combining multiple effectors increased parasite inhibition, with some cases surpassing 89% effectiveness.

## Abstract

Malaria is a significant health problem in the world and has been increased by the emerging resistance to insecticides and antimalarial drugs. New measures must therefore be implemented as an emergency to break the cycle of Plasmodium parasite transmission by the Anopheles mosquitoes. This systematic review assessed the effectiveness of paratransgenesis, an engineering approach that utilizes symbiotic microbes to deliver antiplasmodial molecules into the midgut of the mosquito as a transmission-blocking agent. PubMed, ScienceDirect, and Web of Science were searched in accordance with the PRISMA guidelines, yielding 1,289 records. Ten eligible studies were then included after screening. The chosen articles studied bacterial and fungal symbionts, such as Asaia, Serratia, Pantoea, Enterobacter, and Aspergillus oryzae, that have been engineered to produce effector proteins, such as Scorpine, EPIP, Defensin, and SM1–2 peptides. The delivery of oral sugar meals was always associated with colonization of the mosquito midguts, and results reported high levels of inhibition of oocysts or sporozoites in the mosquitoes. Scorpine was the strongest and most commonly used effector with a high level of up to 97.8% inhibition of P. falciparum oocysts in various microbial systems. The combination of two or multiple-effector approaches increased the efficacy in some cases, surpassing 89% parasite inhibition. The risk of bias measurement showed moderate variation in the methods, yet it was in favor of the sound findings. All evidence suggests that paratransgenesis is a potentially important malaria control tool, complementing existing approaches to malaria control. Nevertheless, ecological safety, microbial stability, and field validation are the key obstacles before the translation to large-scale use.

Malaria is one of the key world health problems, especially in sub-Saharan Africa, where the rising resistance to insecticides and antimalarial drugs is posing a threat to the current control mechanisms. New strategies are urgently needed to break the cycle of the spread of Plasmodium parasites by the Anopheles mosquito. A potential solution is paratransgenesis, which involves the genetic modification of naturally occurring mosquito-associated microbes to produce molecules that prevent the development of parasites in the gut of the mosquito. In this systematic review, we examined experimental studies that investigated paratransgenesis as a malaria control measure. Using the PRISMA guideline, we identified ten eligible studies that had engineered bacterial or fungal symbionts to express antiplasmodial effector proteins. These studies showed that feeding mosquitoes a sugar meal containing engineered microbes resulted in a stable colonization of the mosquito midgut. Several of the molecules tested were highly effective in reducing parasite development, with scorpine consistently showing strong transmission-blocking activity, achieving parasite inhibition rates greater than 90% in different experimental systems. Inhibitory effects were also further augmented by the combination of several effector molecules. Overall, the finding suggests that paratransgenesis has strong potential as an additional malaria control measure. Nevertheless, contests concerning ecological safety, microbial stability, and field implementation will need to be solved before large-scale implementation can be done.