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

Abstract

Background: Aedes-borne diseases such as dengue and chikungunya constitute constant threats globally. In Tanzania, these diseases are transmitted by Aedes aegypti, which is widely distributed in urban areas, but whose ecology remains poorly understood in small towns and rural settings. Methods:A survey of Ae. aegypti aquatic habitats was conducted in and around Ifakara, a fast-growing town in south-eastern Tanzania. The study area was divided into 200 × 200 m search grids, and habitats containing immature Aedes were characterized. Field-collected Ae. aegypti were tested for susceptibility to common public health insecticides (deltamethrin, permethrin, bendiocarb and pirimiphos-methyl) in the dry and rainy seasons. Results:Of 1515 and 1933 aquatic habitats examined in the dry and rainy seasons, 286 and 283 contained Aedes immatures, respectively (container index, CI: 18.9-14.6%). In the 2315 and 2832 houses visited in the dry and rainy seasons, 114 and 186 houses had at least one Aedes-positive habitat, respectively (house index, HI: 4.9-6.6%). The main habitat types included: (i) used vehicle tires and discarded containers; (ii) flowerpots and clay pots; and (iii) holes made by residents on trunks of coconut trees when harvesting the coconuts. Used tires had highest overall abundance of Ae. aegypti immatures, while coconut tree-holes had highest densities per habitat. Aedes aegypti adults were susceptible to all tested insecticides in both seasons, except bendiocarb, against which resistance was observed in the rainy season. Conclusions:To our knowledge, this is the first study on ecology and insecticide susceptibility of Ae. aegypti in Ifakara area, and will provide a basis for future studies on its pathogen transmission activities and control. The high infestation levels observed indicate significant risk of Aedes-borne diseases, requiring immediate action to prevent potential outbreaks in the area. While used tires, discarded containers and flowerpots are key habitats for Ae. aegypti, this study also identified coconut harvesting as an important risk factor, and the associated tree-holes as potential targets for Aedes control. Since Ae. aegypti mosquitoes in the area are still susceptible to most insecticides, effective control could be achieved by combining environmental management, preferably involving communities, habitat removal and insecticide spraying.

High Aedes spp. larval indices in Kinshasa, Democratic Republic of Congo

“…The indices observed here are comparable to those reported for other African settings, e.g. southeastern Tanzania has a HI of 4.9–6.6, and CI of 14.6–18.9 [ 43 ]; Burkina Faso has a HI of 70, a CI of 35 and a BI of 10 [ 44 ]; northwest Ethiopia has a HI of 25.5, a CI of 32.9 and a BI of 48.4 [ 45 ]; Mozambique has a CI of 22 [ 46 ]; and Angola has a HI of 4.3–27.9, a CI of 2.1–9.3 and a BI of 5.8–42.2 [ 47 ]. However, the Aedes larval and pupal indices found in the present study are much lower than those observed in Kenya during a dengue outbreak in 2013–2014, where the BI reached a value of 270 positive containers/100 houses [ 48 ].…”

High Aedes spp. larval indices in Kinshasa, Democratic Republic of Congo

“…In a place like Kinshasa, where dengue is rarely reported [11][12][13][14] and chikungunya and yellow fever cause sporadic outbreaks [21,23,41], we didn't expect to nd such high Aedes larval and pupal indices. The observed indices are comparable to the ones of other African settings: south-eastern Tanzania has a HI of 4.9 -6.6, CI of 14.6-18.9 [42]; Burkina Faso a HI of 70, CI of 35 and BI of 10 [43]; north-west Ethiopia a HI of 25.5, CI of 32.9 and BI of 48.4 [44]; Mozambique a CI of 22 [45]; and Angola a HI of 4.3 -27.9, CI of 2.1-9.3 and BI of 5.8-42.2 [46]. However, the indices were much lower than the one observed in Kenya during a dengue outbreak in 2013-14, where BI reached a value of 270/100 houses [47].…”

Important Aedes Spp. Density Levels in Kinshasa, Democratic Republic of Congo

“…In a place like Kinshasa, where dengue is rarely reported [21][22][23][24] and chikungunya and yellow fever cause sporadic outbreaks [16,18,41], we didn't expect to nd such high Aedes densities. The observed densities are comparable to the ones of other African settings: south-eastern Tanzania has a HI of 4.9 -6.6, CI of 14.6-18.9 [42]; Burkina Faso a HI of 70, CI of 35 and BI of 10 [43]; north-west Ethiopia a HI of 25.5, CI of 32.9 and BI of 48.4 [44]; Mozambique a CI of 22 [45]; and Angola a HI of 4.3 -27.9, CI of 2.1-9.3 and BI of 5.8-42.2 [46]. However, the densities were much lower than the one observed in Kenya during a dengue outbreak in 2013-14, where BI reached a value of 270/100 houses [47].…”