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Background The mosquito Aedes aegypti transmits two of the most serious mosquito-borne viruses, dengue virus (DENV) and Zika virus (ZIKV), which results in significant human morbidity and mortality worldwide. The quickly shifting landscapes of DENV and ZIKV endemicity worldwide raise concerns that their co-circulation through the Ae. aegypti mosquito vector could greatly exacerbate the disease burden in humans. Recent reports have indicated an increase in the number of co-infection cases in expanding co-endemic regions; however, the impact of co-infection on viral infection and the detailed molecular mechanisms remain to be defined. Methods C6/36 (Aedes albopictus) cells were cultured in Dulbecco's modified Eagle medium/Mitsuhashi and Maramorosch Insect Medium (DMEM/MM) (1:1) containing 2% heat-inactivated fetal bovine serum and 1× penicillin/streptomycin solution. For virus propagation, the cells were infected with either DENV serotype 2 (DENV2) strain 16681 or ZIKV isolate Thailand/1610acTw (MF692778.1). Mosquitoes (Ae. aegypti UGAL [University of Georgia Laboratory]/Rockefeller strain) were orally infected with DENV2 and ZIKV through infectious blood-feeding. Results We first examined viral replication activity in cells infected simultaneously, or sequentially, with DENV and ZIKV, and found interspecies binding of viral genomic transcripts to the non-structural protein 5 (NS5). When we challenged Ae. aegypti mosquitos with both DENV2 and ZIKV sequentially to probe similar interactions, virus production and vector susceptibility to infection were significantly enhanced. Conclusions Our results suggest that DENV2 and ZIKV simultaneously establishing infection in the Ae. aegypti mosquito vector may augment one another during replication. The data also implicate the homologous NS5 protein as a key intersection between the flaviviruses in co-infection, highlighting it as a potential target for vector control.

Background Dengue fever is the most rapidly spreading mosquito-borne viral disease globally. More than 2.5 billion people live in dengue-endemic areas. Previous studies suggested an interrelationship between diabetes mellitus (DM) and dengue hemorrhagic fever (DHF). Conversely, glycolysis is a critical metabolic pathway for optimal dengue virus (DENV) replication. However, little is known concerning the effect of glucose on DENV replication in mosquitoes. In this study, we investigated the impact of glucose on DENV replication in mosquitoes Aedes aegypti. Methods Mosquitoes (Ae. aegypti UGAL/Rockefeller strain) were orally infected with DENV (serotype 2, 16681 strain) through infectious blood feeding. The DENV infection and transmission rates were determined by examining mosquito bodies and saliva, respectively, for DENV positivity at different time points after infection. In addition, a reverse genetic approach was applied by introducing double-stranded RNA against genes of interest into the mosquitoes to inhibit gene expression. Results Our data revealed a significant increase of DENV genome levels in mosquitoes consuming an infectious blood meal supplemented with glucose, suggesting that blood glucose is an important factor for viral replication. Interestingly, a significant increase of DENV E protein levels was detected in the saliva 4 days faster in mosquitoes that consumed infectious blood meals supplemented with glucose than in those consuming infectious blood meals alone. Furthermore, we perform RNAi to silence AKT or TOR and investigate the molecular mechanism regulating the glucose-mediated enhancement of viral replication. Silencing of AKT or TOR significantly reduced DENV titers in mosquitoes. Conclusions This study suggested that blood glucose is beneficial to DENV replication and that it facilitates virus transmission in mosquitoes via AKT and TOR signaling. Therefore, our results strengthen our understanding of dengue fever and DM co-morbidity and possibly reveal new targets for specific antiviral therapies. Graphical abstract