Browsing by Author "Ngowo, Halfan S."

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Creating mosquito-free outdoor spaces using transfuthrin-treated chairs and ribbons
(Springer Nature, 2020-03-10) Paliga, John; Finda, Marceline; Killeen, Gerry F.; Ngowo, Halfan S.; Pinda, Polius G.; Okumu, Fredros O.
Background: Residents of malaria-endemic communities spend several hours outdoors performing diferent activities, e.g. cooking, story-telling or eating, thereby exposing themselves to potentially-infectious mosquitoes. This compromises efectiveness of indoor interventions, notably long-lasting insecticide-treated nets (LLINs) and indoor residual spraying (IRS). This study characterized common peri-domestic spaces in rural south-eastern Tanzania, and assessed protective efcacy against mosquitoes of hessian fabric mats and ribbons treated with the spatial repellent, transfuthrin, and ftted to chairs and outdoor kitchens, respectively. Methods: Two hundred households were surveyed, and their most-used peri-domestic spaces physically characterized. Protective efcacies of locally-made transfuthrin-emanating chairs and hessian ribbons were tested in outdoor environments of 28 households in dry and wet seasons, using volunteer-occupied exposure-free double net traps. CDC light traps were used to estimate host-seeking mosquito densities within open-structure outdoor kitchens. Fieldcollected Anopheles arabiensis and Anopheles funestus mosquitoes were exposed underneath the chairs to estimate 24 h-mortality. Finally, The World Health Organization insecticide susceptibility tests were conducted on wild-caught Anopheles from the villages. Results: Approximately half (52%) of houses had verandas. Aside from these verandas, most houses also had peridomestic spaces where residents stayed most times (67% of houses with verandas and 94% of non-veranda houses). Two-thirds of these spaces were sited under trees, and only one third (34.4%) were built-up. The outdoor structures were usually makeshift kitchens having roofs and partial walls. Transfuthrin-treated chairs reduced outdoor-biting An. arabiensis densities by 70–85%, while transfuthrin-treated hessian ribbons ftted to the outdoor kitchens caused 77–81% reduction in the general peri-domestic area. Almost all the feld-collected An. arabiensis (99.4%) and An. funestus (100%) exposed under transfuthrin-treated chairs died. The An. arabiensis were susceptible to non-pyrethroids (pirimiphos methyl and bendiocarb), but resistant to pyrethroids commonly used on LLINs (deltamethrin and permethrin). Conclusion: Most houses had actively-used peri-domestic outdoor spaces where exposure to mosquitoes occurred. The transfuthrin-treated chairs and ribbons reduced outdoor-biting malaria vectors in these peri-domestic spaces, and also elicited signifcant mortality among pyrethroid-resistant feld-caught malaria vectors. These two new prototype formats for transfuthrin emanators, if developed further, may constitute new options for complementing LLINs and IRS with outdoor protection against malaria and other mosquito-borne pathogens in areas where peri-domestic human activities are common.
Habitat characteristics and insecticide susceptibility of Aedes aegypti in the Ifakara area, south-eastern Tanzania
(Springer Nature Switzerland AG., 2020-02-07) Kahamba, Najat F.; Limwagu, Alex J.; Mapua, Salum A.; Msugupakulya, Betwel J.; Msaky, Dickson S.; Kaindoa, Emmanuel W.; Ngowo, Halfan S.; Okumu, Fredros O.
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) fowerpots 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 frst 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 signifcant risk of Aedes-borne diseases, requiring immediate action to prevent potential outbreaks in the area. While used tires, discarded containers and fowerpots are key habitats for Ae. aegypti, this study also identifed 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, efective control could be achieved by combining environmental management, preferably involving communities, habitat removal and insecticide spraying