Studies on the Impact of Bendiocarb Indoor Residual Spraying on Insecticide Resistance of Anopheles Arabiensis Patton and Other Entomological Determinants of Malaria Transmission In the Upper Blue Nile River Basin, Bahirdar Zuria District, Northwestern Ethiopia
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2018-04-06
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Addis Ababa University
Abstract
Studies on the Impact of Bendiocarb Indoor Residual Spraying on Insecticide Resistance of Anopheles arabiensis Patton and other Entomological Determinants of Malaria Transmission in the Upper Blue Nile River Basin, Bahirdar Zuria District, Northwestern Ethiopia
Alemayehu Abate
Department of Zoological Sciences, Addis Ababa University, 2018
In Ethiopia, malaria vector control using indoor residual spraying has been used against Anopheles arabiensis Patton for decades. However, data for the effective residual life of the insecticides used for indoor residual spraying on sprayed surfaces and the impact of these interventions on different entomological risk factors for malaria transmission is insufficient or absent. Therefore, a comparative study was carried out in Andassa and nearby villages, Bahir Dar Zuria District, Upper Blue Nile River Basin, Northwest Ethiopia to estimate the effective residual life of bendiocarb on treated surfaces and the impact of the application of indoor residual spraying on insecticide resistance status, host preferences, sporozoite and entomological inoculation rate, abundance and resting habits of An. arabeinsis Patton. The effects of indoor residual spraying on the composition and abundance of other Anopheles mosquitoes were also assessed.
Susceptibility of Anophels arabiensis to the insecticide used for indoor residual spraying and its residual life on sprayed surfaces was evaluated based on World Health Organization test procedures. Adult mosquitoes were collected from houses located iv
nearby mosquito breeding sites using Center for Disease Control and preventions light trap, pyrethroid spray sheet collection and artificial pit shelters made nearby pyrethroid spray sheet sampling houses. Collected mosquitos were sorted into species using their external morphology and sibling species of the Anopheles gambiae complex were identified by Polymerase Chain Reaction based molecular methods. Enzyme-linked immunosorbent assay was run to determine blood meal sources and Plasmodium infection rates in Anopheles arabiensis.
The effective residual life of bendiocarb on treated surfaces was higher on plastered wall surfaces than on non-plastered wall surfaces. Resistance to bedndiocarb was suspected in Anophels arabiensis (95%) after three successive spraying cycles within three-year‟s time in Andassa, while the vector remained susceptible (99%) in Tikurit, which received only one round spray. Susceptibility status of the vector to fenithrothion, primiphosmethyl and propoxur was unaffected (100%) due to the application of bendiocarb indoor residual spraying. Susceptibility of the vector to DDT, delthamethrin and malathion was improved progressively at both study sites. East African kdr mutation (kdr-e) was detected in Anopheles arabiensis Patton sampled from both study groups.
In total, 8,859 Anopheles mosquitoes were collected among which 70.15% (n = 6, 215), 21.99% (n = 1,948) and (7.86%, n = 696) of them were Anopheles arabienesis, Anopheles pharoensis and Anopheles coustani, respectively. The abundance of Anopheles arabienesis drastically declined after spray, while indoor residual spraying did not influence its resting habits. General estimating equation model showed that indoor residual and time (month and years) played significant role to affect mosquito abundance. The model also showed that sampling methods had significant effect on the number of v
mosquitoes caught. In contrast, the role of the number of human hosts who slept the previous night in mosquito sampling houses was not significant. The relative adjusted reduction in Plasmodium falciparum infection and entomological inoculation rate in Anopheles arabiensis was 100% after indoor residual spraying, while the reduction in human blood meal index was between 3% and 10%.
In conclusion, bendiocarb was effective to reduce vector density, sporozooite rate and entomological inoculation rate in Anopheles arabiensis without affecting the resting habits of the vector. However, effective residual life of bendiocarb is too short on non-plastered wall surfaces to cover the main malaria transmission season; wall plastering is, therefore, recommended to increase insecticide persistence on treated surfaces. East African kdr mution is widely distributed in populations of the main malaria vector signifying the need to implement insecticide resistance management to restore susceptibility of the vector to DDT/pyrethroid and maintain the efficacy of long-lasting insecticide treated mosquito nets that have been used as frontline defense in the control of malaria vectors in Ethiopia in general and the present study site in particular. Resistance to bendiocarb was suspected after three spraying cycles within three-year times, while efficacy to DDT and pyrethroid was not restored within three years‟ time implying that prevention is better than restoration of insecticide resistance in disease vectors. Therefore, insecticide restitance management should be in place in time.
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Keywords
Ethiopia, Anopheles Arabiensis, Bendiocarb, EIR