Sheep Skin Odor Improves Trap Captures of Mosquito Vectors of Rift Valley Fever

Abstract

In recent years, the East African region has seen an increase in arboviral diseases transmitted by blood-feeding arthropods. Effective surveillance to monitor and reduce incidence of these infections requires the use of appropriate vector sampling tools. Here, trapped skin volatiles on fur from sheep, a known preferred host of mosquito vectors of Rift Valley fever virus (RVFV), were used with a standard CDC light trap to improve catches of mosquito vectors. We tested the standard CDC light trap alone (L), and baited with (a) CO2 (LC), (b) animal volatiles (LF), and (c) CO2 plus animal volatiles (LCF) in two highly endemic areas for RVF in Kenya (Marigat and Ijara districts) from March–June and September–December 2010. The incidence rate ratios (IRR) that mosquito species chose traps baited with treatments (LCF, LC and LF) instead of the control (L) were estimated. Marigat was dominated by secondary vectors and host-seeking mosquitoes were 3–4 times more likely to enter LC and LCF traps [IRR = 3.1 and IRR = 3.8 respectively] than the L only trap. The LCF trap captured a greater number of mosquitoes than the LC trap (IRR = 1.23) although the difference was not significant. Analogous results were observed at Ijara, where species were dominated by key primary and primary RVFV vectors, with 1.6-, 6.5-, and 8.5-fold increases in trap captures recorded in LF, LC and LCF baited traps respectively, relative to the control. These catches all differed significantly from those trapped in L only. Further, there was a significant increase in trap captures in LCF compared to LC (IRR = 1.63). Mosquito species composition and trap counts differed between the RVF sites. However, within each site, catches differed in abundance only and no species preferences were noted in the different baited-traps. Identifying the attractive components present in these natural odors should lead to development of an effective odor-bait trapping system for population density-monitoring and result in improved RVF surveillance especially during the inter-epidemic period.

Common Host-Derived Chemicals Increase Catches of Disease-Transmitting Mosquitoes and Can Improve Early Warning Systems for Rift Valley Fever Virus

“…Our findings concur with published literature highlighting the importance of animal skin odors in mosquito attraction [17], [24]–[26]. Among the animal hosts examined, primary RVFV vectors (comprising Ae.…”

“…Like most hematophagous insects, RVFV vectors use olfactory cues to locate their hosts for a blood meal [16], [17] which may involve more than mammalian breath odors such as CO 2, a non-specific semiochemical, commonly used in the CDC light trap. We therefore refined the sensitivity of the existing trapping system for RVFV vectors by combining it with known mammalian host skin-derived semiochemicals in order to target only mosquitoes.…”

Aedes vector–host olfactory interactions in sylvatic and domestic dengue transmission environments

“…Such sensitivity difference could evoke differential responses or behaviours to host odours as previously highlighted [27,28]. Furthermore, because crude host volatiles comprise a mixture of compounds, some components may be attractants or repellents [7,9]. As such, variation in the amounts and ratios of these components released between different individuals could account for differences in trap catches.…”

“…Previous work has identified vertebrate host chemicals mainly from humans that attract mosquitoes [7,8]. The attractive cues are of practical and epidemiologic relevance and have been exploited in disease vector control and/or surveillance [9][10][11]. Vector surveillance is critical for any vector-borne pathogen risk assessment.…”

Perspectives for Diagnosis and Control of Leishmaniasis Based on Volatile Organic Compounds

“…The trap advocated for capture of phlebotomines is the CDC light [11] and these traps have some operational limitations such as the high cost, little specific and contestable accuracy for areas with low phlebotomines occurrence [161]. The use of chemical compounds along with traps aims to make them more specific and efficient, which has also been demonstrated in studies of phlebotomine [124,162,163], as well as other insect vectors of diseases [164,165].…”