Habitat productivity and pyrethroid susceptibility status of Aedes aegypti mosquitoes in Dar es Salaam, Tanzania

Abstract

Background: Aedes aegypti (Diptera: Culicidae) is the main vector of the dengue virus globally. Dengue vector control is mainly based on reducing the vector population through interventions, which target potential breeding sites. However, in Tanzania, little is known about this vector's habitat productivity and insecticide susceptibility status to support evidence-based implementation of control measures. The present study aimed at assessing the productivity and susceptibility status of A. aegypti mosquitoes to pyrethroid-based insecticides in Dar es Salaam, Tanzania. Methods: An entomological assessment was conducted between January and July 2015 in six randomly selected wards in Dar es Salaam, Tanzania. Habitat productivity was determined by the number of female adult A. aegypti mosquitoes emerged per square metre. The susceptibility status of adult A. aegypti females after exposure to 0.05% deltamethrin, 0.75% permethrin and 0.05% lambda-cyhalothrin was evaluated using the standard WHO protocols. Mortality rates were recorded after 24 h exposure and the knockdown effect was recorded at the time points of 10, 15, 20, 30, 40, 50 and 60 min to calculate the median knockdown times (KDT 50 and KDT 95 ). Results:The results suggest that disposed tyres had the highest productivity, while water storage tanks had the lowest productivity among the breeding habitats Of A. aegypti mosquitoes. All sites demonstrated reduced susceptibility to deltamethrin (0.05%) within 24 h post exposure, with mortalities ranging from 86.3 ± 1.9 (mean ± SD) to 96.8 ± 0.9 (mean ± SD). The lowest and highest susceptibilities were recorded in Mikocheni and Sinza wards, respectively. Similarly, all sites demonstrated reduced susceptibility permethrin (0.75%) ranging from 83.1 ± 2.1% (mean ± SD) to 96.2 ± 0.9% (mean ± SD), in Kipawa and Sinza, respectively. Relatively low mortality rates were observed in relation to lambda-cyhalothrin (0.05%) at all sites, ranging from 83.1 ± 0.7 (mean ± SD) to 86.3 ± 1.4 (mean ± SD). The median KDT 50 for deltamethrin, permethrin and lambda-cyhalothrin were 24.9-30. 3 min, 24.3-34.4 min and 26.7-32.8 min, respectively. The KDT 95 were 55.2-90.9 min for deltamethrin, 54.3-94. 6 min for permethrin and 64.5-69.2 min for lambda-cyhalothrin. Conclusions: The productive habitats for A. aegypti mosquitoes found in Dar es Salaam were water storage containers, discarded tins and tyres. There was a reduced susceptibility of A. aegypti to and emergence of resistance against pyrethroid-based insecticides. The documented differences in the resistance profiles of A. aegypti mosquitoes warrants regular monitoring the pattern concerning resistance against pyrethroid-based insecticides and define dengue vector control strategies.

Habitat characteristics and insecticide susceptibility of Aedes aegypti in the Ifakara area, south-eastern Tanzania

“…Since this study was the first of its kind in this geographical area, there were no immediate comparisons for the resistance profiles. However, in studies carried out in Dar es Salaam, Peru and Burkina Faso, resistance to pyrethroids and organophosphate was obvious [20,50,51]. Reduced susceptibility to pyrethroids observed in some of assays, and the resistance seen against bendiocarb in the rainy season are however signs that we must remain vigilant as insecticide resistance could rapidly spread among the vector populations once active control programmes begin.…”

“…Similar to earlier research, this study has shown that Ae. aegypti prefers breeding in clean and stagnant waters [19,20,41]. Common habitats for Ae.…”

“…In each experiment 120-150 mosquitoes were used, so that there were 20-25 individuals per test. Untreated controls were included, and the mosquitoes were initially observed for 60 minutes to observe knockdown at 10,15,20,30,40,50 and 60 min. The exposed and non-exposed mosquitoes were then provided with 10% glucose and maintained at 28.0 ± 1.0 °C and 80 ± 10% relative humidity, then overall mortality observed after 24 hours.…”

“…For example, in coastal Tanzania, used tires and disposed containers were identified as the most common aquatic habitats for Ae. aegypti [11,20]. However, less is known regarding the ecology of these vectors in inland Tanzania, including small towns and rural settings.…”

Habitat characterization and insecticide susceptibility profiles of Aedes aegypti mosquitoes in Ifakara area, south-eastern Tanzania

“…For example, in coastal Tanzania, used tires and disposed containers were identified as commonest aquatic habitats for Ae. aegypti [11,20]. However, less is known regarding the ecology of these vectors in inland Tanzania, including small towns and rural settings.…”