Abstract
Background: Increased global trade, while beneficial economically, can also increase the spread of vector-borne diseases, particularly those transmitted by Aedes mosquitoes spreading via trade routes. Yet, in sub-Saharan Africa, key Aedes-transmitted diseases remain under-studied, as the majority of mosquito-related research focuses on malaria. Given the heightened trade-induced activity at ports of entry, it is particularly crucial to assess the risk of mosquito-borne diseases in these settings. This study compared the risks of disease-transmitting mosquitoes in and around the eastern Tanzanian seaport of Tanga.
Methods: A 200m x 200m grid-based system was used to sample mosquitoes within the port area, and in surrounding areas at 2km, 2.5km, and 5km away, between June and Dec 2023. We characterized mosquito breeding habitats, collected mosquito larvae using standard dippers and tested susceptibility of Aedes aegypti populations to different insecticides. Adult mosquitoes were collected using BG sentinel traps (daytime) and CDC light traps (night-time). Additionally, over 200 port users and neighboring residents were surveyed to assess experiences and perceptions of mosquito biting and disease risks.
Results: There were 2,931 breeding sites, with 60.8% positive for Aedes larvae. The percentage of water-holding containers infested with Aedes immatures, i.e. Container Index (CI), was highest in the port area (66.2%), and lowest 5 km away (44.6%). The port area also had higher proportion of temporary breeding sites (64.9%) compared to surroundings. The adult mosquito surveys found 20,449 mosquitoes including: Ae. aegypti (5.09%), Culex quinquefasciatus (56.17%), Anopheles gambiae (0.08%), Anopheles funestus (0.01%), and Mansonia uniformis (38.72%). Ae. aegypti were more abundant in the port area than in surrounding areas (P<0.001), while Culex and Mansonia species were more abundant outside (P<0.001). Adult Anopheles were found only in the port area, but Anopheles larvae were found both within and outside the port areas. Tests on Ae. aegypti showed susceptibility to bendiocarb and DDT, and resistance to permethrin. Awareness of mosquito-borne diseases among respondents was high for malaria (64.8%), but low for dengue (26.3%) and Chikungunya (1.7%). Most respondents reported being bothered by mosquitoes mostly at night (53.4%) or evening (40.7%). Besides insecticidal bednets, used primarily against malaria, preventive measures for Aedes-borne diseases were limited.
Conclusion: This study identified significant potential risk of Ae. aegypti and associated diseases, but low perception of risk and inadequate personal protection measures in the study area. This low perception of risk highlights the need to improve public knowledge on transmission and control of Aedes-borne diseases.