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 densitymonitoring
and result in improved RVF surveillance especially during the inter-epidemic period.
