A trial of insecticide treated nets for malaria control in Yanomami communities in Amazonas, Venezuela

Doctoral thesis English OPEN
Crestini, Magda Mara Magris

A community randomized controlled trial \ud was carried \ud out \ud in \ud an area of moderate \ud malaria transmission in the Amazon region, \ud in South \ud East Venezuela, \ud where the \ud indigenous Yanomami population \ud live. \ud The \ud aim \ud of the \ud project \ud was to \ud assess \ud the \ud impact of lambdacyhalothrin treated \ud hammock \ud nets \ud (ITHNs), \ud compared \ud to \ud placebo treated hammock nets (PTHNs), on the \ud malaria \ud incidence \ud rate \ud and on \ud the \ud malaria vector population Anopheles darlingi. \ud In both arms of the study intensive early \ud case \ud detection \ud was \ud performed \ud and \ud prompt malaria treatment administered. \ud Baseline \ud data \ud were \ud collected \ud one \ud year \ud before the intervention and a population of \ud around \ud 924 \ud Yanomami \ud was \ud followed \ud for two years. \ud Despite the recent introduction of nets \ud in the \ud Yanomami \ud villages \ud and the \ud adverse \ud natural conditions in the area, the majority of \ud Yanomami \ud showed \ud high \ud compliance \ud and took good care of the nets. \ud Analysis performed by gas chromatography of \ud samples taken from the \ud nets \ud dried \ud in different ways, i. e. vertically or horizontally, in the \ud sun or \ud in the \ud shade, \ud showed \ud that there were no significant differences between \ud methods with the \ud only \ud exception of drying the nets horizontally and \ud in the \ud sun \ud performing \ud significantly \ud worse then the others. In addition \ud bioassays, \ud with \ud Aedes \ud aegypti, \ud showed that \ud hammock nets treated at village level with \ud lambdacyhalothrin (10 \ud mg/m2) and dried vertically in the sun were effectively \ud killing \ud mosquitoes \ud (87%) \ud after six \ud months of regular use and the mortality rate \ud was \ud 83% \ud after washing the \ud nets \ud twice. \ud The malaria incidence rate per thousand person years at risk \ud was \ud 114.6 in the \ud IHTNs group and 186.8 in the PTHNs group. \ud The \ud adjusted rate ratios \ud indicated \ud that ITHNs prevent 55% (IRR: 0.44, 95% CI: 52-59%) \ud of \ud new \ud malaria \ud cases. \ud ITHNs reduced the prevalence of parasitaemia \ud by 87% (RR: 0.17, 95% CI: 0-45%) in the first cross-sectional survey carried out \ud during the \ud high transmission \ud season, six months after the intervention. The \ud prevalence \ud of splenomegaly \ud and of \ud anaemia was low in both groups, and there \ud was no evidence \ud of reduction \ud due to \ud ITHNs. \ud There was little evidence of a mass \ud killing \ud effect \ud on the \ud density \ud of the \ud vector \ud population, although significant differences between \ud study arms \ud were \ud found \ud when \ud the analysis was carried out adjusting \ud for baseline \ud An. \ud darlingi \ud density. \ud The \ud density of An. darlingi was 62% less in \ud villages \ud with \ud ITHNs than those \ud with \ud PTHNs (density ratio: 0.38, 95% CI 52-70%). \ud The main conclusion of the present study \ud is that ITHNs \ud can reduce malaria \ud incidence in the area and it is the most \ud feasible \ud method \ud of malaria control \ud in \ud a \ud forested area where indigenous villages are \ud scattered over \ud a \ud large territory.
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