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The mosquito Aedes aegypti is distributed worldwide and is recognized as the primary vector for dengue in numerous countries. To investigate whether the fitness cost of a single DENV-1 isolate varies among populations, we selected four Ae. aegypti populations from distinct localities: Australia (AUS), Brazil (BRA), Pakistan (PAK), and Peru (PER). Utilizing simple methodologies, we concurrently assessed survival rates and fecundity. Overall, DENV-1 infection led to a significant decrease in mosquito survival rates, with the exception of the PER population. Furthermore, infected Ae. aegypti from PAK, the population with the lowest infection rate among those tested, exhibited a noteworthy reduction in egg laying. These findings collectively suggest that local mosquito-virus adaptations may influence dengue transmission in endemic settings.

Several countries have been using Wolbachia deployments to replace highly competent native Aedes aegypti populations with Wolbachia -carrying mosquitoes with lower susceptibility to arboviruses such as dengue, Zika, and chikungunya. In Rio de Janeiro, Wolbachia deployments started in 2015 and still present a moderate introgression with a modest reduction in dengue cases in humans (38%). Here, we evaluated the vector competence of wild-type and w Mel-infected Ae. aegypti with a Brazilian genetic background to investigate whether virus leakage could contribute to the observed outcomes in Brazil. We collected the specimens in three areas of Rio de Janeiro with distinct frequencies of mosquitoes with w Mel strain and two areas with wild Ae. aegypti . The mosquitoes were orally exposed to two titers of DENV-1 and the saliva of DENV-1-infected Ae. aegypti was microinjected into w Mel-free mosquitoes to check their infectivity. When infected with the high DENV-1 titer, the presence of w Mel did not avoid viral infection in mosquitoes' bodies and saliva but DENV-1-infected w Mel mosquitoes produced lower viral loads than w Mel-free mosquitoes. On the other hand, w Mel mosquitoes infected with the low DENV-1 titer were less susceptible to virus infection than w Mel-free mosquitoes, although once infected, w Mel and w Mel-free mosquitoes exhibited similar viral loads in the body and the saliva. Our results showed viral leakage in 60% of the saliva of w Mel mosquitoes with Brazilian background; thus, sustained surveillance is imperative to monitor the presence of other circulating DENV-1 strains capable of overcoming the Wolbachia blocking phenotype, enabling timely implementation of action plans.