Location: Arthropod-borne Animal Diseases ResearchTitle: Mosquito host choices on livestock amplifiers of Rift Valley fever virus in Kenya
|TCHOUASSI, DAVID - International Centre Of Insect Physiology And Ecology|
|OKIRO, ROBINSON - International Centre Of Insect Physiology And Ecology|
|SANG, ROSEMARY - International Centre Of Insect Physiology And Ecology|
|TORTO, BALDWYN - International Centre Of Insect Physiology And Ecology|
Submitted to: Parasites & Vectors
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/23/2016
Publication Date: 3/31/2016
Citation: Tchouassi, D.P., Okiro, R., Sang, R., Cohnstaedt, L.W., McVey, D.S., Torto, B. 2016. Mosquito host choices on livestock amplifiers of Rift Valley fever virus in Kenya. Parasites & Vectors. 9:184-191.
Interpretive Summary: An increase in the biting rate of the mosquitoes would be expected to result in increased pathogen transmission to susceptible hosts, all other conditions being equal. In the case of RVF amplifiers examined, we observed an overall increased attraction and engorgement of mosquitoes on cow relative to sheep and goat. This confirms higher biting pressure of the community of mosquitoes examined on cattle. However, attraction did not always translate into feeding success and this latter most important epidemiologic parameter did not seem to vary for specific species among the hosts notably the flood water Aedes species, the primary vectors of RVFV. The overall high attractiveness of the mosquitoes to cow suggest when used as bait it can be exploited in the monitoring and control of disease-causing mosquitoes by incorporating say a tent impregnated with insecticide as in our experimental design. This approach can be employed as an intervention tool during arbovirus disease outbreaks to divert significant bites away from humans to livestock where they are then killed. Based on high attraction and engorgement to anophelines and particularly the malaria vectors, use of cattle as baits may be a promising approach in the fight against malaria. This may be of great value against outdoor biting fractions which remains an important focus of sustaining malaria and out of reach of current indoor vector control tools such indoor residual spray and long lasting insecticide treated bednets.
Technical Abstract: Animal hosts may vary in their attraction and acceptability as components of the host location process for assessing biting rates of vectors and risk of exposure to pathogens. However, these parameters remain poorly understood for mosquito vectors of the Rift Valley fever (RVF), an arboviral disease, and for a community of mosquitoes. Using three known livestock amplifiers of RVF virus including sheep, goat and cattle as baits in enclosure traps, we investigated in a longitudinal study for six months (June – November 2015) the host-feeding patterns for a community of mosquitoes in Naivasha, an endemic area of Rift Valley fever (RVF). We estimated the incidence rate ratios (IRR) that mosquitoes chose cow over the other livestock hosts by comparing their attraction (total number collected) and engorgement rate (proportion freshly blood-fed) on these hosts. Overall, significant differences were observed in host preference parameters for attraction (F2,15=4.1314, P=0.037) and engorgement (F2,15= 6.24, P=0.01) with cow consistently attracting about 3-fold as many mosquitoes and those engorged than sheep (attraction: IRR=2.9 95%CI (1.24-7.96; engorgement: IRR=3.2, 95%CI=1.38-7.38) or goat (attraction: IRR=2.7; 95%CI (1.18-7.16); engorgement: IRR=3.28; 95%CI (1.47-7.53). However, there was no difference between the attraction elicited by sheep and goat (IRR=1.08; 95%CI (0.35-3.33) or engorgement rate (IRR=0.96, 95%CI=0.36-2.57). Despite the overall attractive pattern on cow, the engorgement rate was clearly independent of the number attracted for certain mosquito species, notably among the flood water Aedes species, largely incriminated previously as primary vectors of RVF. Our findings suggest that insecticide treated cattle (ITC) can be exploited in enclosure traps as contact baits in the monitoring and control of disease-causing mosquitoes in RVF endemic areas.