Relative performance of indoor vector control interventions in the Ifakara and the West African experimental huts

Welbeck A Oumbouke,Augustin Fongnikin,Sarah J Moore,Koffi B Soukou,Raphael N’Guessan

doi:10.1186/s13071-017-2365-4

Welbeck A Oumbouke, Augustin Fongnikin + Show 3 more

Open Access

https://doi.org/10.1186/s13071-017-2365-4

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Abstract

BackgroundWest African and Ifakara experimental huts are used to evaluate indoor mosquito control interventions, including spatial repellents and insecticides. The two hut types differ in size and design, so a side-by-side comparison was performed to investigate the performance of indoor interventions in the two hut designs using standard entomological outcomes: relative indoor mosquito density (deterrence), exophily (induced exit), blood-feeding and mortality of mosquitoes.MethodsMetofluthrin mosquito coils (0.00625% and 0.0097%) and Olyset® Net vs control nets (untreated, deliberately holed net) were evaluated against pyrethroid-resistant Culex quinquefasciatus in Benin. Four experimental huts were used: two West African hut designs and two Ifakara hut designs. Treatments were rotated among the huts every four nights until each treatment was tested in each hut 52 times. Volunteers rotated between huts nightly.ResultsThe Ifakara huts caught a median of 37 Culex quinquefasciatus/ night, while the West African huts captured a median of 8/ night (rate ratio 3.37, 95% CI: 2.30–4.94, P < 0.0001) and this difference in mosquito entry was similar for Olyset® Net and more pronounced for spatial repellents. Exophily was greater in the Ifakara huts with > 4-fold higher mosquito exit relative to the West African huts (odds ratio 4.18, 95% CI: 3.18–5.51, P < 0.0001), regardless of treatment. While blood-feeding rates were significantly higher in the West African huts, mortality appeared significantly lower for all treatments.ConclusionsThe Ifakara hut captured more Cx. quinquefasciatus that could more easily exit into windows and eave traps after failing to blood-feed, compared to the West African hut. The higher mortality rates recorded in the Ifakara huts could be attributable to the greater proportions of Culex mosquitoes exiting and probably dying from starvation, relative to the situation in the West African huts.

Highlights

West African and Ifakara experimental huts are used to evaluate indoor mosquito control interventions, including spatial repellents and insecticides
During the Global Malaria Eradication Campaign (1955–1969) the need to evaluate the efficacy of residual insecticides such as DDT and Dieldrin for malaria campaigns motivated the development of experimental huts
Huts of the same design were constructed in a row, and the West African huts were located behind the Ifakara experimental huts

Summary

Introduction

West African and Ifakara experimental huts are used to evaluate indoor mosquito control interventions, including spatial repellents and insecticides. The Ifakara hut design [3] is a modified version of the “Portable hut” designed in Belize, Central America [4] that has similar dimensions to Tanzanian homes and includes features of East African hut designs including baffles to prevent mosquito egress [5], window traps [6] but with eave traps rather than verandah traps to capture mosquitoes that exit through eave gaps [7] Both the West African and Ifakara huts are used to evaluate in WHO phase II trials the efficacy of mosquito control interventions, including insecticide [8,9,10] and repellentbased products [11, 12]. The question of whether the efficacy of a candidate indoor intervention changes with experimental hut design remains unaddressed

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