Abstract:
BACKGROUND : Effective surveillance and estimation of the biting fraction of Aedes aegypti is critical for accurate
determination of the extent of virus transmission during outbreaks and inter-epidemic periods of dengue and
chikungunya fever. Here, we describe the development and use of synthetic human odor baits for improved sampling
of adult Ae. aegypti, in two dengue and chikungunya fevers endemic areas in Kenya; Kilifi and Busia counties.
METHODS : We collected volatiles from the feet and trunks of two female and two male volunteers aged between 25
and 45 years. We used coupled gas chromatography- electroantennographic detection (GC/EAD) analysis to screen
for antennally-active components from the volatiles and coupled GC-mass spectrometry (GC/MS) to identify the
EAD-active components. Using randomized replicated designs, we compared the efficacies of Biogents (BG) sentinel
traps baited with carbon dioxide plus either single or blends of the identified compounds against the BG sentinel trap
baited with carbon dioxide plus the BG commercial lure in trapping Ae. aegypti. The daily mosquito counts in the
different traps were subjected to negative binomial regression following the generalized linear models procedures.
RESULTS : A total of ten major EAD-active components identified by GC/MS as mainly aldehydes and carboxylic acids,
were consistently isolated from the human feet and trunk volatiles from at least two volunteers. Field assays with
synthetic chemicals of the shared EAD-active components identified from the feet and trunk gave varying results. Ae.
aegypti were more attracted to carbon dioxide baited BG sentinel traps combined with blends of aldehydes than to
similar traps combined with blends of carboxylic acids. When we assessed the efficacy of hexanoic acid detected in
odors of the BG commercial lure and volunteers plus carbon dioxide, trap captures of Ae. aegypti doubled over the trap
baited with the commercial BG lure. However, dispensing aldehydes and carboxylic acids together in blends, reduced
trap captures of Ae. aegypti by ~45%-50%.
CONCLUSIONS : Our results provide evidence for roles of carboxylic acids and aldehydes in Ae. aegypti host attraction and
also show that of the carboxylic acids, hexanoic acid is a more effective lure for the vector than the BG commercial lure.
