Presentation Abstract

Session: Mosquitoes: Insecticide Resistance and Control
Abstract Number: 968
Title: Resistance to pyrethroid and carbamate threatens vector control in West of Tanzania
Presentation Start: 11/13/2012 4:30:00 PM
Authors: Natacha Protopopoff1, Robert Malima2, Alex Wright1, Reginald Kavishe3, Johnson Matowo3, Philippa West1, Franklin W. Mosha3, Immo Kleinschmidt1, Mark Rowland1
1London School of Hygiene and Tropical Medicine, London, United Kingdom, 2National Institute for Medical Research, Muheza, Tanzania, United Republic of, 3Kilimanjaro Christian Medical College, Moshi, Tanzania, United Republic of
Abstract: Kagera region on the western side of Lake Victoria had the highest malaria burden in Tanzania according the 2007 Malaria Indicator Survey. To reduce malaria transmission an annual round of indoor residual spraying (IRS) has been conducted since 2007 initially with lambdacyhalothrin (pyrethroid) and more recently with bendiocarb (carbamate). A campaign of universal coverage of long lasting insecticidal nets (LLIN) was carried out in 2011. The emergence of resistance could threaten the future of these two interventions. As a component of a cluster randomized trial comparing the combination of LLIN and IRS versus LLIN alone the distribution of vectors and prevalence of insecticide resistance is being monitored. From April to December 2011, monthly Anopheles collection using CDC light traps was carried out across 40 villages in the area. Resistance monitoring was carried out on An. gambiae s.l. using WHO cylinder test. CDC bottle bioassays with synergists examined the involvement of metabolic resistance. Species identification and prevalence of knock down resistance (kdr) was confirmed using real time PCR TaqMan assay. A total of 5844 Anopheles mosquitoes were collected over seven months, of these 67% were collected in April, two months after spraying with pyrethroid. 81.8% were An.gambiae s.s. and 17.2% were An. arabiensis. East kdr mutation which is associated with pyrethroid and DDT resistance was present at high frequency in An.gambiae s.s. (97%) but only at 5% in An.arabiensis. Mortality in WHO resistance tests ranged from 0% to 38% for lambdacyhalothin, 12% to 40% for DDT, and 84% to 100% for bendiocarb. Result from the CDC bottle assay suggested the presence of elevated level of oxidases and esterases. East kdr mutation seems to have reached fixation in the An.gambiae s.s population. High phenotypic resistance to pyrethroid was observed. In contrast to neighbouring Kenya where An.gambiae s.s. nearly disappeared after vector control despite high kdr frequency, An.gambiae s.s. remains predominant in Kagera even with high coverage of pyrethroid IRS and LLINs.

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