Silent Circulation of Dengue Virus in Aedes aegypti Mosquitoes in Non-Epidemic Regions of Tanzania: Implications for Surveillance and Control.

Objective: This study aimed to assess the prevalence of dengue virus (DENV) infection in Aedes aegypti mosquitoes and evaluate associated ecological and environmental factors in three inland districts (Bahi, Kyela, Ngorongoro) with distinct agro-ecological characteristics and no prior dengue outbreak reports.

Methods: A cross-sectional entomological study was conducted during the wet (April-June 2022) and dry (October-November 2022) seasons. Adult mosquitoes were collected indoors and outdoors using battery-powered aspirators, and immature stages were sampled from natural and artificial water containers. Mosquito pools were screened for DENV RNA using RT-qPCR.

Results: A total of 6459 Ae. aegypti mosquitoes were sampled (54% females). DENV RNA was detected in 0.6% (4/631) of the tested pools: one from Bahi and three from Kyela. No infections were detected in Ngorongoro. High mosquito density was observed in Kyela, particularly in paddy plantations and rice farms. Among DENV-positive pools, 100% (4/4) were collected near vegetation, suggesting that outdoor habitats are high-risk sites. The minimum infection rate was 0.6 (95% CI: 0.2-1.6) per 1000 mosquitoes.

Conclusion: This study confirms silent DENV circulation in Ae. aegypti populations in Tanzanian regions without prior epidemic reports. The detection of DENV in mosquitoes from Bahi and Kyela highlights the risk of future outbreaks and underscores the need for enhanced vector surveillance and integrated control strategies. These findings emphasise the urgency of preemptive public health measures to mitigate dengue spread in Tanzania. Limitations of the study include reliance on RT-qPCR without viral isolation or serotyping and the absence of concurrent human clinical data.