Abstract
Experimental huts are part of the WHO process for testing and evaluation of Insecticide Treated Nets (ITN) in semi-field conditions. Experimental Hut Trials (EHTs) mostly focus on two main indicators (i.e., mortality and blood feeding reduction) that serve as efficacy criteria to obtain WHO interim recommendation. However, several other outputs that rely on counts of vectors collected in the huts are neglected although they can give useful information about vectors’ behavior and personal protection provided by ITNs. In particular, EHTs allow to measure the deterrent effect and personal protection of ITNs. To provide a better assessment of ITNs efficacy, we performed a retrospective analysis of the deterrence and the personal protection against malaria transmission for 12 unwashed and 13 washed ITNs evaluated through EHTs conducted in West Africa. A significant deterrent effect was shown for six of the 12 unwashed ITNs tested. When washed 20 times, only three ITNs had significant deterrent effect (Rate Ratios (RR)<1; p<0.05) and three showed an apparent “attractiveness” (RR>1; p<0.01). When compared to the untreated net, all unwashed ITNs showed lower number of blood-fed Anopheles indicating a significant personal protection (RR<1, p<0.05). However, when washed 20 times, three ITNs that were found to be attractive did not significantly reduce human-vector contact (p>0.05). Current WHO efficacy criteria do not sufficiently take into account the deterrence effect of ITNs. Moreover, the deterrence variability is rarely discussed in EHT’s reports. Our findings highlighted the long-range effect (deterrent or attractive) of ITNs that may have significant consequences for personal/community protection against malaria transmission. Indicators measuring the deterrence should be further considered for the evaluation of ITNs.
Highlights
Between 2000 and 2015, the scale-up of malaria control interventions helped to reduce malaria mortality by 60% globally, and by 66% in sub-Saharan Africa (SSA)
To illustrate the importance of the deterrence on the estimation of the personal protection of a Long Lasting Insecticidal Nets (LLIN) product, we address the relationships among the blood-feeding inhibition (BFI), the deterrence and the personal protection: for a given value of BFI, the personal protection provided by an Insecticide Treated Nets (ITN) could be either positive, null, or negative depending on the deterrence
To provide a better assessment of ITNs used for malaria control, we performed a retrospective analysis of the deterrence and the personal protection against malaria transmission for 13 ITNs evaluated through Experimental Hut Trials (EHTs)
Summary
The blood-feeding inhibition (BFI) is defined as “the reduction in blood-feeding in comparison with the control huts” [4]. It is not very clear from this definition, “blood-feeding” must be understand as “blood-feeding rate” (i.e. the proportion of blood-fed mosquitoes in the huts) but not as absolute number of blood-fed mosquitoes collected in the huts. The personal protection (PP) against transmission provided by a treatment in an experimental hut study is determined by the reduction in the number of blood-fed mosquitoes in the treatment hut relative to the number of blood-fed mosquitoes in the control hut: PP 1⁄4 1 À Bt ð3Þ Bc
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