title: Modelling Vaccination Strategies against Rift Valley Fever in Livestock in Kenya.
abstract: The impacts of vaccination on the transmission of Rift Valley fever virus (RVFV) have not been evaluated. We have developed a RVFV transmission model comprising two hosts-cattle as a separate host and sheep and goats as one combined host (herein after referred to as sheep)-and two vectors-Aedes species (spp) and Culex spp-and used it to predict the impacts of: (1) reactive vaccination implemented at various levels of coverage at pre-determined time points, (2) targeted vaccination involving either of the two host species, and (3) a periodic vaccination implemented biannually or annually before an outbreak.
  
  
  
  The model comprises coupled vector and host modules where the dynamics of vectors and hosts are described using a system of difference equations. Vector populations are structured into egg, larva, pupa and adult stages and the latter stage is further categorized into three infection categories: susceptible, exposed and infectious mosquitoes. The survival rates of the immature stages (egg, larva and pupa) are dependent on rainfall densities extracted from the Tropical Rainfall Measuring Mission (TRMM) for a Rift Valley fever (RVF) endemic site in Kenya over a period of 1827 days. The host populations are structured into four age classes comprising young, weaners, yearlings and adults and four infection categories including susceptible, exposed, infectious, and immune categories. The model reproduces the 2006/2007 RVF outbreak reported in empirical surveys in the target area and other seasonal transmission events that are perceived to occur during the wet seasons. Mass reactive vaccination strategies greatly reduce the potential for a major outbreak. The results also suggest that the effectiveness of vaccination can be enhanced by increasing the vaccination coverage, targeting vaccination on cattle given that this species plays a major role in the transmission of the virus, and using both periodic and reactive vaccination strategies.
  
  
  
  Reactive vaccination can be effective in mitigating the impacts of RVF outbreaks but practically, it is not always possible to have this measure implemented satisfactorily due to the rapid onset and evolution of RVF epidemics. This analysis demonstrates that both periodic and reactive vaccination ought to be used strategically to effectively control the disease.
authors.affiliation: School of Public Health, Jomo Kenyatta University of Agriculture and Technology, Juja, Kenya.|International Livestock Research Institute, Nairobi, Kenya.
authors.forename: John M
authors.identifier: 0000-0001-9854-7490
authors.initials: JM
authors.lastname: Gachohi
authors.affiliation: Kenya Medical Research Institute (KEMRI), Nairobi, Kenya.
authors.forename: M Kariuki
authors.initials: MK
authors.lastname: Njenga
authors.affiliation: Faculty of Veterinary Medicine, University of Nairobi, Nairobi, Kenya.
authors.forename: Philip
authors.initials: P
authors.lastname: Kitala
authors.affiliation: International Livestock Research Institute, Nairobi, Kenya.
authors.forename: Bernard
authors.initials: B
authors.lastname: Bett
mesh_terms: D000330:Aedes / Q000821:virology; D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000453:epidemiology / Q000517:prevention & control / Q000635:transmission; D003465:Culex / Q000821:virology; D004196:Disease Outbreaks; D058872:Epidemics; D015511:Goat Diseases / Q000276:immunology / Q000517:prevention & control / Q000635:transmission; D006041:Goats; D058507:Host Specificity; D007630:Kenya / Q000453:epidemiology; D008954:Models, Biological; D000072138:Mosquito Vectors / Q000821:virology; D012295:Rift Valley Fever / Q000453:epidemiology* / Q000276:immunology / Q000517:prevention & control* / Q000635:transmission; D012296:Rift Valley fever virus / Q000276:immunology*; D012756:Sheep; D012757:Sheep Diseases / Q000276:immunology / Q000517:prevention & control / Q000635:transmission; D014611:Vaccination / Q000379:methods / Q000662:veterinary*; D014765:Viral Vaccines / Q000008:administration & dosage*
chemical_list: D014765:Viral Vaccines