Abstract
Catches of Anopheles gambiae and An. arabiensis with the Ifakara Tent Trap-model B (ITT-B) correlate better with human landing catches than any other method but fail to reduce the proportion of blood-fed mosquito caught, which indicates that users are exposed to bites during collection. An improved C model (ITT-C) was developed and evaluated by comparing with ITT-B in semi-field and full-field conditions in southern Tanzania. The sensitivity of the ITT-C was approximately two times that of the ITT-B: relative rate (95% confidence interval) = 1.92 (1.52–2.42), 1.90 (1.48–2.43), and 2.30 (1.54–3.30) for field populations of An. arabiensis, Culex spp., and Mansonia spp., respectively. The ITT-C caught 73% less blood-fed An. arabiensis than the ITT-B in open field experiments and none in semi-field experiments, which confirmed that the C design is a safe trapping method. Validation of ITT-C by comparison with human landing catches and parasitologic measures of human infection status may be necessary to confirm that this design produces consistent and epidemiologically meaningful results.
Highlights
Catches of Anopheles gambiae and An. arabiensis with the Ifakara Tent Trap-model B (ITT-B) correlate better with human landing catches than any other method but fail to reduce the proportion of blood-fed mosquito caught, which indicates that users are exposed to bites during collection
The ITT-C consistently sampled approximately twice as many mosquitoes as the ITT-B for all three genera. This difference was significant for An. gambiae s.l., the only malaria vector present in sufficient numbers, and for Culex spp. and Mansonia spp. (Table 2)
Of 366 successfully amplified specimens of An. gambiae s.l. caught in the field experiment, 97% (355) and 3% (11) were An. arabiensis and An. gambiae sensu stricto, respectively
Summary
In the drive to eliminate malaria, mosquito sampling measures are crucial for monitoring changes in human exposure to infections and the effect of vector-control interventions.[1,2,3] existing monitoring methods for adult stages of the Anopheles vectors of human malaria all have significant limitations, where densities of malaria-transmitting mosquitoes are low.[4,5,6] This technology has become increasingly important as malaria control,[7,8,9] elimination, and eradication[10] are prioritized by policy makers and significant progress towards lower transmission levels is achieved.[6,11,12,13,14,15] Standard entomologic methods often fail to detect[16] low levels of malaria transmission. A new device for sampling malaria vectors in Africa, called the Ifakara Tent Trap-design B (ITT-B), has recently been developed and evaluated as a means to catch malaria vector mosquitoes under conditions of low and high mosquito densities in Tanzania.[18] The relative sensitivity of ITT-B increased as vector density decreased and exceeded that of human landing catches at the lowest densities[18] in urban Dar es Salaam. ITT-B failed to reduce the proportions of blood-fed mosquito caught relative to that observed in sample obtained by human landing catches.[18,19] The biggest disadvantage of the human landing catch method is the inevitable exposure of human participants to mosquito bites.[2,3,20] ITT-B operators may have been exposed to mosquito bites.[18,19] Alternatively, these traps may act as resting shelters for freshly fed mosquitoes, and both of these possibilities may cause blood-fed mosquitoes to be caught in the field
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