The consequence of simultaneous and sequential coinfections of Aedes aegypti with DENV-1, DENV-2, and CHIKV on vector competence

Vector-borne diseases (VBD) caused by arboviruses represent a major public health threat in tropical regions. According to WHO’s Global Vector Control Response, more than 80% of the global population live in areas at risk for VBD. For instance, Aedes aegypti is the primary vector of dengue virus (DENV) and chikungunya virus (CHIKV), and its widespread distribution, particularly in Brazil, contributes to the occurrence of outbreaks. During these outbreaks, mosquitoes may acquire either monoinfections or coinfections, which can occur either simultaneously or sequentially, potentially influencing transmission dynamics. In this study, we investigated the effects of simultaneous coinfection with CHIKV and two DENV serotypes (DENV-1 and DENV-2) on the vector competence of Ae. aegypti and described the characteristics of infection and transmission phenotypes following different orders of sequential arbovirus acquisition. Simultaneous coinfection resulted in serotype-dependent outcomes. At 7 days post-infection (dpi), DENV-1 infection rates and viral loads were significantly reduced compared with monoinfections, whereas DENV-2 showed increased viral loads in saliva. At 14 dpi, CHIKV infection rates were significantly reduced in both the CHIKV+DENV-1 (CD1) and CHIKV+DENV-2 (CD2) groups, whereas CHIKV viral loads were reduced only in the CD2 group. In the sequential coinfection experiments, DENV-2 exhibited lower replication levels than DENV-1 in both sequential infection scenarios, regardless of whether DENV was acquired before or after CHIKV. Likewise, DENV-2 showed lower transmission efficiency than DENV-1, and murine transmission assays confirmed reduced viral loads for DENV-2. Overall, our findings demonstrate that CHIKV–DENV coinfection in Ae. aegypti is associated with distinct infection and transmission outcomes depending on the DENV serotype and the infection scenario. In sequentially exposed mosquitoes, distinct phenotypes were observed according to the order of arbovirus acquisition. These results highlight the complexity of arboviral coinfections within this shared vector and emphasize the importance of considering different coinfection scenarios when evaluating vector competence and transmission risk in endemic settings.