Habitat characterization and insecticide susceptibility profiles of <i>Aedes aegypti</i> mosquitoes in south-eastern, Tanzania
Creators: name: Kahamba, Najat
name: Limwagu, Alex
name: Salum Mapua
name: Betwel Msugupakulya
name: Dickson Msaky
name: Kaindoa, Emmanuel
name: Halfan Ngowo
name: Fredros Okumu
Publisher: name: Gates Open Research
Year: 2019

description: <i>Aedes</i>-borne infections such as dengue and chikungunya constitute constant threats globally. In Tanzania, the most important vector of these diseases is <i>Aedes aegypti</i>, which is widely distributed in urban areas, but whose ecology remains poorly-understood in small towns and rural settings. We surveyed the aquatic habitats of <i>Ae. aegypti</i> mosquitoes in and around Ifakara, a fast-growing town in south-eastern Tanzania. The area was divided into 200m × 200m search grids, and habitats containing <i>Ae. aegypti</i> larvae or pupae characterized physically. Additionally, using WHO guidelines, we examined susceptibility of field-collected <i>Aedes</i> to common public health insecticides, i.e. pyrethroids (permethrin, 0.75% and deltamethrin, 0.05%), organophosphate (pirimiphos methyl, 0.25%), carbamate (bendiocarb, 0.1%) and organochloride (dieldrin, 4%), in both dry and rainy seasons (Nov-2018 to May-2019). A total of 1,515 and 1,933 larval habitats were visited and characterized in the dry and rainy season. Of these only 286 (18.87%) and 283 (14.64%) contained <i>Aedes</i> immatures. A total of 2,315 and 2,832 houses were visited in the dry and rainy season surveys, out of which, 114 (4.9%) and 186 (6.6%) houses had at least one positive breeding site respectively. Majority of <i>Ae. aegypti</i> habitats were associated with improper garbage disposal (used tires and discarded containers), peri-domestic aesthetics and water storage (flower pots and clay pots) or coconut harvesting (holes made by residents on trunks of coconut trees to support climbing harvesters). Used tires had highest overall abundance of <i>Aedes</i> immatures, while coconut tree holes had highest densities per habitat. Habitats containing <i>Ae. aegypti</i> had clear stagnant water, mostly in shaded areas. The mosquitoes were susceptible to all insecticides in both seasons, except bendiocarb, which had reduced susceptibility during rainy season tests. This is the first study on ecology and insecticide susceptibility of <i>Aedes</i> mosquitoes in this area, and will provide a basis for future evaluation of its role in pathogen transmission, as well as options for its control. Infestation levels observed indicate that immediate actions should be taken to prevent outbreaks. The larval indices (container index, house index and breteaux index) are high enough to signal significant risk of <i>Aedes</i>-borne diseases in the area. We also recommend that similar assessments should be done in other towns and their surrounding areas. Addition to that, such research should involve community to help eradicate the breeding sites through an integrated environmental management program leveraging on any existing initiatives such as the monthly clean-up campaigns in Tanzania. Fortunately, the <i>Ae. aegypti</i> in the area are still susceptible to majority of insecticides used in public health, indicating available opportunities to include insecticides in the control programs. While used tires, discarded containers and flower pots are key habitats for <i>Aedes</i> in the area, this study also identified coconut harvesting as an important risk factor, and the associated tree-holes as vital targets for <i>Aedes</i> control.