Efficacy of the D-Design Ifakara Tent Trap for Sampling Malaria Vectors in An Area of Mass Long Lasting Insecticidal Bed Nets Use

Abstract

The quest to develop alternative mosquito surveillance tools that substitute for Human Landing Catches and that are effective, exposure free and easy to use has resulted in the development of a variety of traps. These include Centres for Disease Control miniature light traps, Ifakara Tent Traps, Mbita traps, Furvela tent traps and Back Pack Aspirators. With the global agenda currently mentored to eradicate malaria, effective sampling tools that can detect low mosquito vector densities and low transmission levels will be increasingly needed so that successful control programmes can monitor and manage their efforts to achieve local elimination. Ifakara Tent Trap (ITT) was a promising outdoor mosquito sampling tool. The Band C designs of the ITT have previously proven to have acceptable sampling sensitivity levels in urban and rural Tanzania. However, they require a large amount of space to set up due to the ropes and pegs used to stretch them horizontally. In this study, the D design (lIT-D), modified from C design (ITT-C) and which uses a smaller space, was evaluated in parallel with ITT-C and CDC-LT in Lupiro in southern Tanzania where ITT-B and C had been earlier proven effective relative to CDC-LT or HLC. Surprisingly, both ITT-C and ITT-D exhibited very poor sampling sensitivity relative to CDC-LT with relative rates, at 95% CI, 0.131 (0.119 - 0.144) and 0.044 (0.37 - 0.51) respectively. The mean catches for IIT-C, ITT-D and CDC-LT was 12.4 ± 18.77, 3.96 ± 0.424 and 90.5 ±18.77 respectively. To understand the reason for this reduced efficiency of ITT -C, F 1 generation of Lupiro An. arabiensis of 2011, laboratory reared An. arabiensis adults from Sakamaganga and Lupiro colonized in 2008 and 2009 respectively, were compared on their likelihood to enter ITT-C. The wild mosquito populations in Lupiro of 2011 were less likely to enter ITT-C, relative rate 0.056 (95% CL 0.015 - 0.201, P< 0.001). Lupiro 2009 colony were more likely to enter ITT-C, relative rate 0.813 (95% CL 0.415-l.5010, P= 0.545). From time of development of ITT, time trend analysis of trap's sampling sensitivity from conducted studies showed declining trapping sensitivity. This study showed that, in addition to other factors not investigated due to resource limitation, reluctance by Lupiro 2011 mosquito population to enter ITT-C appears to be a heritable trait passed to offspring. This reluctance to enter ITT-C appears to be associated with altered host-seeking patterns resulting from scale up ofLLIN use in Kilombero Valley. It was thus concluded that ITT-D was not a better tool for sampling malaria vectors in this valley.