title: Association of ecological factors with Rift Valley fever occurrence and mapping of risk zones in Kenya.
abstract: OBJECTIVE
  Rift Valley fever (RVF) is a mosquito-borne infection with great impact on animal and human health. The objectives of this study were to identify ecological factors that explain the risk of RVF outbreaks in eastern and central Kenya and to produce a spatially explicit risk map.
  
  
  METHODS
  The sensitivity of seven selected ecological variables to RVF occurrence was assessed by generalized linear modelling (GLM). Vegetation seasonality variables (from normalized difference vegetation index (NDVI) data) and 'evapotranspiration' (ET) (metrics) were obtained from 0.25-1km MODIS satellite data observations; 'livestock density' (N/km(2)), 'elevation' (m), and 'soil ratio' (fraction of all significant soil types within a certain county as a function of the total area of that county) were used as covariates.
  
  
  RESULTS
  'Livestock density', 'small vegetation integral', and the second principal component of ET were the most significant determinants of RVF occurrence in Kenya (all p ≤ 0.01), with high RVF risk areas identified in the counties of Tana River, Garissa, Isiolo, and Lamu.
  
  
  CONCLUSIONS
  Wet soil fluxes measured with ET and vegetation seasonality variables could be used to map RVF risk zones on a sub-regional scale. Future outbreaks could be better managed if relevant RVF variables are integrated into early warning systems.
authors.affiliation: International Centre of Insect Physiology and Ecology, PO Box 30772-00100, Nairobi, Kenya.
authors.forename: Gladys
authors.initials: G
authors.lastname: Mosomtai
authors.affiliation: Department of Clinical Microbiology, Virology, Umeå University, Umeå, Sweden.
authors.forename: Magnus
authors.initials: M
authors.lastname: Evander
authors.affiliation: Department of Forest Resource Management, Faculty of Forest Sciences, Swedish University of Agricultural Sciences, Umeå, Sweden.
authors.forename: Per
authors.initials: P
authors.lastname: Sandström
authors.affiliation: Department of Clinical Microbiology, Infectious Diseases, Umeå University, Umeå, Sweden.
authors.forename: Clas
authors.initials: C
authors.lastname: Ahlm
authors.affiliation: International Centre of Insect Physiology and Ecology, PO Box 30772-00100, Nairobi, Kenya.
authors.forename: Rosemary
authors.initials: R
authors.lastname: Sang
authors.affiliation: Department of Clinical Microbiology, Virology, Umeå University, Umeå, Sweden.
authors.forename: Osama Ahmed
authors.initials: OA
authors.lastname: Hassan
authors.affiliation: International Centre of Insect Physiology and Ecology, PO Box 30772-00100, Nairobi, Kenya.
authors.forename: Hippolyte
authors.initials: H
authors.lastname: Affognon
authors.affiliation: International Centre of Insect Physiology and Ecology, PO Box 30772-00100, Nairobi, Kenya. Electronic address: tlandmann@icipe.org.
authors.forename: Tobias
authors.initials: T
authors.lastname: Landmann
mesh_terms: D000818:Animals; D009033:Culicidae / Q000821:virology*; D004196:Disease Outbreaks; D004463:Ecology; D005843:Geography; D006801:Humans; D007630:Kenya / Q000453:epidemiology; D058751:Livestock; D012295:Rift Valley Fever / Q000453:epidemiology*; D012296:Rift Valley fever virus / Q000302:isolation & purification*; D012306:Risk; D012988:Soil Microbiology
keywords: Animal density; Disease mapping; Evapotranspiration; Normalized difference vegetation index; Rift Valley fever