Common host-derived chemicals increase catches of disease-transmitting mosquitoes and can improve early warning systems for Rift Valley fever virus

Abstract

Rift Valley fever (RVF), a mosquito-borne zoonosis, is a major public health and veterinary problem in sub-Saharan Africa. Surveillance to monitor mosquito populations during the inter-epidemic period (IEP) and viral activity in these vectors is critical to informing public health decisions for early warning and control of the disease. Using a combination of field bioassays, electrophysiological and chemical analyses we demonstrated that skin-derived aldehydes (heptanal, octanal, nonanal, decanal) common to RVF virus (RVFV) hosts including sheep, cow, donkey, goat and human serve as potent attractants for RVFV mosquito vectors. Furthermore, a blend formulated from the four aldehydes and combined with CO(2)-baited CDC trap without a light bulb doubled to tripled trap captures compared to control traps baited with CO(2) alone. Our results reveal that (a) because of the commonality of the host chemical signature required for attraction, the host-vector interaction appears to favor the mosquito vector allowing it to find and opportunistically feed on a wide range of mammalian hosts of the disease, and (b) the sensitivity, specificity and superiority of this trapping system offers the potential for its wider use in surveillance programs for RVFV mosquito vectors especially during the IEP.

Figure 1. Map of Kenya showing the location of the study sites.

Figure 2. Trap design using CDC trap without a light bulb for field evaluation.

(A) crude animal skin odors: arrangement of canister and CO₂ released at the bottom of the Igloo container all placed close to the fan of the trap; (B) synthetic compounds released from a 0.5 ml tube placed under the Igloo close to the air flow of CO₂.

Figure 3. Mean daily captures of RVFV vectors in the different trap treatments in 11 replicate trials.

(A) primary vectors (Ae. mcintoshi and Ae. ochraceus); secondary vectors comprising (B) total Culex spp.; (C) total Mansonia spp. Control, CO₂-baited traps only; host treatments represent skin odors from each host type combined with CO₂. Treatments followed by the same letters are not significantly different at P = 0.05 following generalized linear model (GLM) with negative binomial error structure and log link in R 2.11.0 software; Error bars indicate standard error of the mean.

Figure 4. Representative GC-EAD profiles using wild caught adult female Ae. mcintoshi to the different host odors.

(A) Cow (B) Donkey (C) Human (D) Goat (E) Sheep. Upper traces are FID (chemical profile) of the respective host odor and lower traces are EAD responses. Regardless of host type, similar responses to the four aldehydes (whose peaks are labeled in the uppermost trace) were reproducibly recorded not only in this species but in Ae. ochraceus and diverse species of Culex and Mansonia which are secondary RVFV vectors (n = 3). (Scale bar in all the GC-EAD runs, 1 mV.)