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London School of Hygiene & Tropical Medicine Malaria Centre

Malaria research in vector studies

Combined use of Indoor Residual Spraying (IRS) and Long-Lasting Insecticidal Nets (LLINs) for malaria reduction in endemic rural Tanzania

LSHTM investigators:
Natacha Protopopoff, Philippa West, Alexandra Wright, Immo Kleinschmidt & Mark Rowland.
External collaborators:
Frank Mosha & Reginald Kavishe (Kilimanjaro Christian Medical Colleges, Tanzania), Robert Malima & William Kisinza (National Institute for Medical Research, Tanzania).
Funding body:
President’s Malaria Initiative.

Numerous studies have shown that long lasting insecticidal nets (IRS) and indoor residual spraying (LLINs) are effective in preventing malaria.

What is less certain is the added value of combining both. The present study aims to evaluate the impact of combining IRS and LLINs compared to LLINs alone on malaria prevalence through a two-arm cluster randomized trial. The study is being carried out in Muleba district to the west of Lake Victoria in Tanzania. During this baseline year both arms of the study area received IRS with pyrethroid and universal LLIN coverage. IRS coverage reaches 95% of households and net usage increased from 41% to 56% after the LLIN mass distribution campaign. Result from two household and malaria prevalence cross-sectional surveys among children under 15 years showed an overall prevalence of 9.3% (5000 children) in February and 22.8% in July (4315 children). Seven monthly rounds of cross sectional mosquito collection using CDC light traps were conducted between April and December. A total of 12819 mosquitoes were collected of which 46% were Anopheles. A high frequency of resistance to pyrethroid and DDT was observed among Anopheles gambiae s.l. with mortality to these insecticides in WHO tests less than 40%. During the intervention year (2012), two more cross sectional malaria prevalence surveys are planned and 12 rounds of light trap collection.