Fine-scale spatial and temporal heterogeneities in insecticide resistance profiles of the malaria vector, Anopheles arabiensis in rural south-eastern Tanzania

Matowo, N. S., Munhenga, G., Tanner, M., Coetzee, M., Feringa, W. F., Ngowo, H. S. , Koekemoer, L. L. and Okumu, F. O. (2017) Fine-scale spatial and temporal heterogeneities in insecticide resistance profiles of the malaria vector, Anopheles arabiensis in rural south-eastern Tanzania. Wellcome Open Research, 2, 96. (doi: 10.12688/wellcomeopenres.12617.1) (PMID:29417094) (PMCID:PMC5782413)

Abstract

Background: Programmatic monitoring of insecticide resistance in disease vectors is mostly done on a large scale, often focusing on differences between districts, regions or countries. However, local heterogeneities in residual malaria transmission imply the need for finer-scale data. This study reports small-scale variations of insecticide susceptibility in Anopheles arabiensis between three neighbouring villages across two seasons in Tanzania, where insecticidal bed nets are extensively used, but malaria transmission persists. Methods: WHO insecticide susceptibility assays were conducted on female and male An. arabiensis from three proximal villages, Minepa, Lupiro, and Mavimba, during dry (June-December 2015) and wet (January-May 2016) seasons. Adults emerging from wild-collected larvae were exposed to 0.05% lambda-cyhalothrin, 0.05% deltamethrin, 0.75% permethrin, 4% DDT, 4% dieldrin, 0.1% bendiocarb, 0.1% propoxur, 0.25% pirimiphos-methyl and 5% malathion. A hydrolysis probe assay was used to screen for L1014F (kdr-w) and L1014S (kdr-e) mutations in specimens resistant to DDT or pyrethroids. Synergist assays using piperonly butoxide (PBO) and triphenol phosphate (TPP) were done to assess pyrethroid and bendiocarb resistance phenotypes. Results: There were clear seasonal and spatial fluctuations in phenotypic resistance status in An. arabiensis to pyrethroids, DDT and bendiocarb. Pre-exposure to PBO and TPP, resulted in lower knockdown rates and higher mortalities against pyrethroids and bendiocarb, compared to tests without the synergists. Neither L1014F nor L1014S mutations were detected. Conclusions: This study confirmed the presence of pyrethroid resistance in An. arabiensis and showed small-scale differences in resistance levels between the villages, and between seasons. Substantial, though incomplete, reversal of pyrethroid and bendiocarb resistance following pre-exposure to PBO and TPP, and absence of kdr alleles suggest involvement of P450 monooxygenases and esterases in the resistant phenotypes. We recommend, for effective resistance management, further bioassays to quantify the strength of resistance, and both biochemical and molecular analysis to elucidate specific enzymes responsible in resistance.

• Item Type: Articles
• Additional Information: This work was supported by the Wellcome Trust [102350], Intermediate Research Fellowship awarded to FOO, and [104029], Masters Fellowship in Public Health and Tropical Medicine awarded to the lead author NSM under the mentorship of MC, LLK, and FOO. MC is funded by the DST/NRF South African Research Chairs Initiative.
• Keywords: Anopheles arabiensis, spatial and temporal variations, Tanzania, insecticide resistance, kdr detection, malaria control, metabolic .resistance
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Ngowo, Halfan and Okumu, Professor Fredros
• Authors: Matowo, N. S., Munhenga, G., Tanner, M., Coetzee, M., Feringa, W. F., Ngowo, H. S., Koekemoer, L. L., and Okumu, F. O.
• College/School: College of Medical Veterinary and Life Sciences > School of Biodiversity, One Health & Veterinary Medicine
• Journal Name: Wellcome Open Research
• Publisher: F1000Research
• ISSN: 2398-502X
• ISSN (Online): 2398-502X
• Copyright Holders: Copyright © 2017 Matowo NS et al.
• First Published: First published in Wellcome Open Research 2: 96
• Publisher Policy: Reproduced under a Creative Commons License