Plant based insect repellent and insecticide treated bed nets to protect against malaria in areas of early evening biting vectors: double blind randomised placebo controlled clinical trial in the Bolivian Amazon

doi:10.1136/bmj.39356.574641.55

BMJ, doi: 10.1136/bmj.39356.574641.55, (Published 16 October 2007)

Research

Plant based insect repellent and insecticide treated bed nets to protect against malaria in areas of early evening biting vectors: double blind randomised placebo controlled clinical trial in the Bolivian Amazon

N Hill, principal science officer¹, A Lenglet, research fellow¹, A M Arnéz, senior clinical scientist², I Carneiro, lecturer¹

¹ Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London WC1E 7HT, ² National Bureau of Malaria Control, Ministry of Health, La Paz, Bolivia

Correspondence to: N Hill nigel.hill{at}lshtm.ac.uk

Objective To determine the effectiveness in reducing malariaof combining an insect repellent with insecticide treated bednets compared with the nets alone in an area where vector mosquitoesfeed in the early evening.

Design A double blind, placebo controlled cluster-randomisedclinical study.

Setting Rural villages and peri-urban districts in the BolivianAmazon.

Participants 4008 individuals in 860 households.

Interventions All individuals slept under treated nets; onegroup also used a plant based insect repellent each evening,a second group used placebo.

Main outcome measure Episodes of Plasmodium falciparum or Pvivax malaria confirmed by rapid diagnostic test or blood slide,respectively.

Results We analysed 15 174 person months at risk and found ahighly significant 80% reduction in episodes of P vivax in thegroup that used treated nets and repellent (incidence rate ratio0.20, 95% confidence interval 0.11 to 0.38, P<0.001). Numbersof P falciparum cases during the study were small and, afteradjustment for age, an 82% protective effect was observed, althoughthis was not significant (0.18, 0.02 to 1.40, P=0.10). Reportedepisodes of fever with any cause were reduced by 58% in thegroup that used repellent (0.42, 0.31 to 0.56, P<0.001).

Conclusions Insect repellents can provide protection againstmalaria. In areas where vectors feed in the early evening, effectivenessof treated nets can be significantly increased by using repellentbetween dusk and bedtime. This has important implications inmalaria vector control programmes outside Africa and shows thatthe combined use of treated nets and insect repellents, as advocatedfor most tourists travelling to high risk areas, is fully justified.

Registration NCT 00144716.

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