title: Combining hydrology and mosquito population models to identify the drivers of Rift Valley fever emergence in semi-arid regions of West Africa.
abstract: BACKGROUND
  Rift Valley fever (RVF) is a vector-borne viral zoonosis of increasing global importance. RVF virus (RVFV) is transmitted either through exposure to infected animals or through bites from different species of infected mosquitoes, mainly of Aedes and Culex genera. These mosquitoes are very sensitive to environmental conditions, which may determine their presence, biology, and abundance. In East Africa, RVF outbreaks are known to be closely associated with heavy rainfall events, unlike in the semi-arid regions of West Africa where the drivers of RVF emergence remain poorly understood. The assumed importance of temporary ponds and rainfall temporal distribution therefore needs to be investigated.
  
  
  RESULTS
  A hydrological model is combined with a mosquito population model to predict the abundance of the two main mosquito species (Aedes vexans and Culex poicilipes) involved in RVFV transmission in Senegal. The study area is an agropastoral zone located in the Ferlo Valley, characterized by a dense network of temporary water ponds which constitute mosquito breeding sites. The hydrological model uses daily rainfall as input to simulate variations of pond surface areas. The mosquito population model is mechanistic, considers both aquatic and adult stages and is driven by pond dynamics. Once validated using hydrological and entomological field data, the model was used to simulate the abundance dynamics of the two mosquito species over a 43-year period (1961-2003). We analysed the predicted dynamics of mosquito populations with regards to the years of main outbreaks. The results showed that the main RVF outbreaks occurred during years with simultaneous high abundances of both species.
  
  
  CONCLUSIONS
  Our study provides for the first time a mechanistic insight on RVFV transmission in West Africa. It highlights the complementary roles of Aedes vexans and Culex poicilipes mosquitoes in virus transmission, and recommends the identification of rainfall patterns favourable for RVFV amplification.
authors.affiliation: CIRAD, UPR AGIRs, Montpellier, France.
authors.forename: Valérie
authors.initials: V
authors.lastname: Soti
authors.forename: Annelise
authors.initials: A
authors.lastname: Tran
authors.forename: Pascal
authors.initials: P
authors.lastname: Degenne
authors.forename: Véronique
authors.initials: V
authors.lastname: Chevalier
authors.forename: Danny
authors.initials: D
authors.lastname: Lo Seen
authors.forename: Yaya
authors.initials: Y
authors.lastname: Thiongane
authors.forename: Mawlouth
authors.initials: M
authors.lastname: Diallo
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Guégan
authors.forename: Didier
authors.initials: D
authors.lastname: Fontenille
mesh_terms: D000330:Aedes / Q000254:growth & development*; D000354:Africa, Western; D000818:Animals; D003465:Culex / Q000254:growth & development*; D003889:Desert Climate; D005260:Female; D006801:Humans; D011156:Population Density; D011157:Population Dynamics; D012295:Rift Valley Fever / Q000453:epidemiology* / Q000635:transmission*; D014887:Weather; D015047:Zoonoses / Q000453:epidemiology* / Q000635:transmission*