title: Effects of Irrigation and Rainfall on the Population Dynamics of Rift Valley Fever and Other Arbovirus Mosquito Vectors in the Epidemic-Prone Tana River County, Kenya.
abstract: Rift Valley fever (RVF) is a mosquito-borne viral zoonosis that is found in most regions of sub-Saharan Africa, and it affects humans, livestock, and some wild ungulates. Outbreaks are precipitated by an abundance of mosquito vectors associated with heavy persistent rainfall with flooding. We determined the impact of flood-irrigation farming and the effect of environmental parameters on the ecology and densities of primary and secondary vectors of the RVF virus (RVFV) in an RVF-epidemic hotspot in the Tana River Basin, Kenya. Mosquito sampling was conducted in farms and villages (settlements) in an irrigated and a neighboring nonirrigated site (Murukani). Overall, a significantly higher number of mosquitoes were collected in farms in the irrigation scheme compared with villages in the same area (P < 0.001), or farms (P < 0.001), and villages (P = 0.03) in Murukani. In particular, key primary vectors of RVFV, Aedes mcintoshi Marks and Aedes ochraceous Theobald, were more prevalent in the farms compared with villages in the irrigation scheme (P = 0.001) both during the dry and the wet seasons. Similarly, there was a greater abundance of secondary vectors, particularly Culex univittatus Theobald and Culex pipiens (L.) in the irrigation scheme than in the Murukani area. Rainfall and humidity were positively correlated with mosquito densities, particularly the primary vectors. Adult floodwater mosquitoes and Mansonia spp. were collected indoors; immatures of Ae. mcintoshi and secondary vectors were collected in the irrigation drainage canals, whereas those of Ae. ochraceous and Aedes sudanensis Theobald were missing from these water bodies. In conclusion, irrigation in RVF endemic areas provides conducive resting and breeding conditions for vectors of RVFV and other endemic arboviruses.
authors.affiliation: Center for Virus Research, Kenya Medical Research Institute, P. O. Box 54840-00200, Mbagathi Way, Nairobi, Kenya (rosemary.sang@usamru-k.org; Joel.Lutomiah@usamru-k.org; albina.makio@usamru-k.org; hellen.koka@usamru-k.org; edith.koskei@usamru-k.org; albert.nyunja@usamru-k.org; samuel.owaka@usamru-k.org; dmatoke@kemri.org).
authors.forename: R
authors.initials: R
authors.lastname: Sang
authors.affiliation: Center for Virus Research, Kenya Medical Research Institute, P. O. Box 54840-00200, Mbagathi Way, Nairobi, Kenya (rosemary.sang@usamru-k.org; Joel.Lutomiah@usamru-k.org; albina.makio@usamru-k.org; hellen.koka@usamru-k.org; edith.koskei@usamru-k.org; albert.nyunja@usamru-k.org; samuel.owaka@usamru-k.org; dmatoke@kemri.org).
authors.forename: J
authors.initials: J
authors.lastname: Lutomiah
authors.affiliation: Food Safety and Zoonosis Research Program, International Livestock Research Institute, P. O. Box 30709-00100, Nairobi, Kenya (msaid362@gmail.com; j.lindahl@cgiar.org; d.grace@cgiar.org; b.bett@cgiar.org).
authors.forename: M
authors.initials: M
authors.lastname: Said
authors.affiliation: Center for Virus Research, Kenya Medical Research Institute, P. O. Box 54840-00200, Mbagathi Way, Nairobi, Kenya (rosemary.sang@usamru-k.org; Joel.Lutomiah@usamru-k.org; albina.makio@usamru-k.org; hellen.koka@usamru-k.org; edith.koskei@usamru-k.org; albert.nyunja@usamru-k.org; samuel.owaka@usamru-k.org; dmatoke@kemri.org).
authors.forename: A
authors.initials: A
authors.lastname: Makio
authors.affiliation: Center for Virus Research, Kenya Medical Research Institute, P. O. Box 54840-00200, Mbagathi Way, Nairobi, Kenya (rosemary.sang@usamru-k.org; Joel.Lutomiah@usamru-k.org; albina.makio@usamru-k.org; hellen.koka@usamru-k.org; edith.koskei@usamru-k.org; albert.nyunja@usamru-k.org; samuel.owaka@usamru-k.org; dmatoke@kemri.org).
authors.forename: H
authors.initials: H
authors.lastname: Koka
authors.affiliation: Center for Virus Research, Kenya Medical Research Institute, P. O. Box 54840-00200, Mbagathi Way, Nairobi, Kenya (rosemary.sang@usamru-k.org; Joel.Lutomiah@usamru-k.org; albina.makio@usamru-k.org; hellen.koka@usamru-k.org; edith.koskei@usamru-k.org; albert.nyunja@usamru-k.org; samuel.owaka@usamru-k.org; dmatoke@kemri.org).
authors.forename: E
authors.initials: E
authors.lastname: Koskei
authors.affiliation: Center for Virus Research, Kenya Medical Research Institute, P. O. Box 54840-00200, Mbagathi Way, Nairobi, Kenya (rosemary.sang@usamru-k.org; Joel.Lutomiah@usamru-k.org; albina.makio@usamru-k.org; hellen.koka@usamru-k.org; edith.koskei@usamru-k.org; albert.nyunja@usamru-k.org; samuel.owaka@usamru-k.org; dmatoke@kemri.org).
authors.forename: A
authors.initials: A
authors.lastname: Nyunja
authors.affiliation: Center for Virus Research, Kenya Medical Research Institute, P. O. Box 54840-00200, Mbagathi Way, Nairobi, Kenya (rosemary.sang@usamru-k.org; Joel.Lutomiah@usamru-k.org; albina.makio@usamru-k.org; hellen.koka@usamru-k.org; edith.koskei@usamru-k.org; albert.nyunja@usamru-k.org; samuel.owaka@usamru-k.org; dmatoke@kemri.org).
authors.forename: S
authors.initials: S
authors.lastname: Owaka
authors.affiliation: Center for Virus Research, Kenya Medical Research Institute, P. O. Box 54840-00200, Mbagathi Way, Nairobi, Kenya (rosemary.sang@usamru-k.org; Joel.Lutomiah@usamru-k.org; albina.makio@usamru-k.org; hellen.koka@usamru-k.org; edith.koskei@usamru-k.org; albert.nyunja@usamru-k.org; samuel.owaka@usamru-k.org; dmatoke@kemri.org).
authors.forename: D
authors.initials: D
authors.lastname: Matoke-Muhia
authors.affiliation: Institute of Anthropology, University of Nairobi, P.O. Box 30079-00100, Nairobi, Kenya (sallybukachi@yahoo.com).
authors.forename: S
authors.initials: S
authors.lastname: Bukachi
authors.affiliation: Food Safety and Zoonosis Research Program, International Livestock Research Institute, P. O. Box 30709-00100, Nairobi, Kenya (msaid362@gmail.com; j.lindahl@cgiar.org; d.grace@cgiar.org; b.bett@cgiar.org).
authors.forename: J
authors.initials: J
authors.lastname: Lindahl
authors.affiliation: Food Safety and Zoonosis Research Program, International Livestock Research Institute, P. O. Box 30709-00100, Nairobi, Kenya (msaid362@gmail.com; j.lindahl@cgiar.org; d.grace@cgiar.org; b.bett@cgiar.org).
authors.forename: D
authors.initials: D
authors.lastname: Grace
authors.affiliation: Food Safety and Zoonosis Research Program, International Livestock Research Institute, P. O. Box 30709-00100, Nairobi, Kenya (msaid362@gmail.com; j.lindahl@cgiar.org; d.grace@cgiar.org; b.bett@cgiar.org).
authors.forename: B
authors.initials: B
authors.lastname: Bett
mesh_terms: D057914:Agricultural Irrigation; D000818:Animals; D001103:Arboviruses / Q000502:physiology*; D009033:Culicidae / Q000145:classification / Q000254:growth & development* / Q000502:physiology / Q000821:virology; D017753:Ecosystem; D006801:Humans; D007630:Kenya / Q000453:epidemiology; D000072138:Mosquito Vectors / Q000145:classification / Q000254:growth & development* / Q000502:physiology / Q000821:virology; D011157:Population Dynamics; D011891:Rain / Q000737:chemistry; D012295:Rift Valley Fever / Q000453:epidemiology / Q000635:transmission* / Q000821:virology; D012296:Rift Valley fever virus / Q000502:physiology
keywords: Ae. mcintoshi; Rift Valley fever; ecology; irrigation scheme; rainfall