Browsing by Author "Joseph, Rosalia N"

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    The efficacy of indoor residual spraying and insecticide susceptibility status of the Anopheles mosquito population from selected malaria endemic regions of Northern Namibia
    (University of Namibia, 2021) Joseph, Rosalia N; Mumbengegwi, Davis R
    Indoor residual spraying (IRS) and long-lasting insecticidal nets (LLINs) are the primary malaria vector control interventions recommended by the World Health Organisation (WHO). These interventions have been used in northern Namibia as the main intervention for malaria vector control since the 1965 (IRS) and 2005 (LLINs). However, insecticide resistance (IR) in Anopheles mosquitoes to pyrethroids, a major insecticide class approved for use in both LLINs and IRS of modem structures, may threaten continued use of these interventions. This study aimed to evaluate the susceptibility status and composition of Anopheles mosquitoes and the efficacy of indoor residual spraying insecticides in northern regions. Data was collected at one point in time and not throughout the year. WHO bioassay tubes were used to investigate the susceptibility status of Anopheles mosquitoes from Otjozondjupa, Omusati, Oshana, Ohangwena, Kavango West, Kunene and Oshikoto region to DDT ( 4 %) and Deltamethrin (0.05 %) insecticide. The Anopheles mosquitoes were then morphologically identified; as well as molecularly identified to a species level using the Polymerase Chain Reaction (PCR) method. Residual efficacy of insecticides DDT, Deltamethrin, pirimiphosmethyl (Actellic 300CS), and clothianidin (SumiShield 50 WG) sprayed on zinc, modem and traditional structures in Oshana region was also tested with susceptible Anopheles arabiensis, using WHO cone bioassays. Findings confirmed IR against Deltamethrin in Oshikoto and Kavango West region (78.75 % and 90 % respectively) according to WHO protocols, with other malaria regions showing reduced susceptibility. There is reduced susceptibility to DDT in Kavango West region (93.75 %), while all other regions showed full susceptibility (100 %). PCR results showed an overall predominance of Anopheles gambiae sensu stricto (982) over Anopheles arabiensis (600) in northern Namibia; Otjozondjupa (214, 13 7), Omusati (183, 123), Oshana (196, 48), Ohangwena (163, 167), Kavango West (41 , 54), Kunene (113, 0), Oshikoto (72, 71), respectively. Five months after initial application, SumiShield 50WG induced 100% mortality of mosquitoes exposed on both modern and zinc structures, Deltamethrin killed more than 80 % of mosquitoes on these structures, although Actellic 300CS and DDT were below the threshold recommended. There is a prevalence of pyrethroid resistance in Namibian malaria vectors in Kavango West and Oshikoto regions, which might hinder vector management. However, SumiShield SOWG an environmentally acceptable insecticide with a it ren t 111 oJc of action to pyrethroids may be a suitable alternative insecticide for IRS in Nami bia, where resistance to Deltamethrin and DDT insecticide has started to develop. SumiShield 50WG is a novel neonicotinoid insecticide that acts as an agonist of the nicotinic acetylcholine receptor (nAChR). This receptor differs from those of the existing recommended insecticide families (pyrethroids, organophosphates, carbamates and organochlorine). Although, continued IR surveillance is recommended in more than one sentinel site of the malaria endemic regions of Namibia, monitoring should start earlier to avoid incomplete tests due to insufficient sample size. Additionally, it is recommended that the residual efficacy study should be repeated with a sufficient number of structures and sufficient mosquito sample size