Abstract
Mosquitoes are responsible for more than one million deaths annually by transmitting mosquito-borne pathogens across over 190 countries. Understanding mosquito–pathogen interactions offers a potential path for developing strategies to reduce vector competence and thereby lessen the global health burden of mosquito-borne diseases. Zika virus (ZIKV) is among the most recently emerging mosquito-borne pathogens, while Semliki Forest virus (SFV) serves as a widely used alphavirus model. Despite extensive research into their effects on mosquito physiology, most studies have been conducted under simplified conditions—examining limited genetic responses in a single organ or time point, or relying on injection-based infection models that fail to replicate the natural oral infection route. Dengue virus (DENV), which causes the highest global disease burden among arboviruses, has prompted practical research into controlling viral replication in mosquitoes, particularly through the use of Wolbachia. However, the physiological changes induced by DENV–Wolbachia interactions in mosquitoes remain poorly characterized, and the underlying mechanisms are not fully understood. The overall aim of this thesis was to systematically elucidate ZIKV– and SFV–mosquito interactions and uncover the molecular mechanisms underlying the Wolbachia effect, with the goal of identifying candidate genes for vector competence control.The first aim was to characterize the temporal and organ-specific responses of Aedes aegypti females to blood feeding and oral infection with ZIKV and SFV. Using a factorial experimental design encompassing three time points post-blood meal (days 2, 8, and 17) and multiple organs (midgut, salivary glands, thorax, ovary, head, and whole body), we generated a comprehensive transcriptomic atlas describing the progression of infection and physiological change. The analysis revealed that blood feeding itself, rather than viral infection, was the primary driver of mosquito transcriptional regulation across the body. A globally suppressed transcriptional response may be the potential hallmark of mosquito-borne viral infection.
The second aim was to elucidate the Wolbachia–DENV interaction, focusing on the mosquito midgut as a critical site for regulating vector competence. Aedes aegypti infected with Wolbachia were either left untreated or cleared of the symbiont using antibiotics prior to oral DENV infection. Midgut mRNA profiles were then characterized by transcriptomic analysis, alongside investigations into midgut cell regeneration. The findings show that Wolbachia plays a central role in activating mosquito immunity and protecting midgut integrity during DENV infection, predominantly via the redox pathway with NADPH-regulating genes, which may lead to oxidative stress by Reactive Oxygen Species (ROS) production.
The third aim was to determine which NADPH oxidase gene—Dual oxidase (Duox), NADPH oxidase (Nox), or both—serves as the principal regulator of midgut immunity in the ROS pathway. To address this, mosquitoes were subjected to RNA interference targeting either Duox, Nox, or a non-related control gene (LacZ), followed by oral infection with Erwinia carotovora 15 (ECC15), a well-characterized insect pathogen. Subsequent transcriptomic profiling and assessments of midgut cell repair revealed that Nox, rather than Duox, is the key functional gene mediating ROS-related immunity, thereby representing a likely molecular target underpinning the Wolbachia effect on vector competence.
Collectively, this thesis advances our understanding of mosquito–virus interactions by providing the first multi-organ, multi-time point transcriptomic characterization of ZIKV and SFV infection under natural oral feeding conditions, and by identifying Nox as a central mediator of Wolbachia-driven modulation of vector competence. These findings not only elucidate fundamental aspects of mosquito biology but also suggest promising molecular targets for the development of novel vector control strategies.
| Date of Award | 8 Dec 2025 |
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| Original language | English |
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| Supervisor | Patrick BUTAYE (Supervisor), Nicolas BUCHON (External Co-Supervisor), Guan YANG (Co-supervisor) & Olivier Andre SPARAGANO (External Co-Supervisor) |