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Irrigation and the risk of Rift Valley fever transmission - a case study from Kenya

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Presentation by Dr Bernard Bett of the International Livestock Research Institute, Nairobi, at the One Health for the Real World: zoonoses, ecosystems and wellbeing symposium, London 17-18 March 2016

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Irrigation and the risk of Rift Valley fever transmission - a case study from Kenya

  1. 1. Irrigation and the risk of Rift Valley fever transmission – a case study from Kenya Bernard Bett, International Livestock Research Institute
  2. 2. Acknowledgements Said Mohammed1, Rosemary Sang2, Salome Bukachi3, Johanna Lindahl1, Salome Wanyoike4, Ian Njeru5, Delia Grace1 1. International Livestock Research Institute, Nairobi 2. Kenya Medical Research Institute, Mbagathi Way, Nairobi 3. Institute of Anthropology, Gender and African Studies, Nairobi 4. Department of Veterinary Services, Ministry of Agriculture, Nairobi 5. Division of Disease Surveillance and Response, Ministry of Public Health, Nairobi Dynamic Drivers of Disease in Africa REF:NE/J001422/1”
  3. 3. • RVF: • Mosquito-borne viral zoonosis • High and persistent rainfall • Would irrigation promote endemic RVF? • Irrigation and trade offs in ecosystem services  Water and food  Risk of vector-borne diseases Irrigated site with stagnant water in the drainage canals – source of water for people but also breeding grounds for mosquitoes Rift Valley fever case study
  4. 4. • The study site: • Arid/semi-arid region in northeastern Kenya • Two irrigation schemes and adjacent pastoral areas • Studies: oEcological/GIS analyses – Entomological surveys oParticipatory studies and socio-economic surveys oSero-epidemiological surveys in livestock and people • Support to policy makers to improve disease surveillance and response Methods Study site in Kenya, GIS team, ILRI
  5. 5. 20 0 20 40 60 80 Kilometers N Open shrubs (65-40% crown cover) Very open shrubs (40-15% crown cover) Closed herbaceous vegetation on permanently flooded land Open to closed herbaceous vegetation on temporarily flooded Open to closed herbaceous vegetation Irrigated land / Cropland Clouds Tana River-Waterbodies Urban and Rural Settements Open trees on temporarily flooded land Trees and shrubs savannah Very open trees (40-15% crown cover) Open trees (65-40% crown cover) Closed trees Legenda) 1975 b) 2010 Ecological analyses: Land cover changes between 1975 and 2010
  6. 6. Activities – Field sites • Mosquito sampling o 6pm-6am for 3 consecutive days/site • Livestock and human sampling o Blood sampling o Serum extraction and storage o Sample screening using ELISA kits • Data analyzed using geostatistical models to account for spatial effect Field surveys Animal sampling, B.Bett, ILRI CDC light trap for mosquitoes, B.Bett, ILRI
  7. 7. Participatory and socio-economic surveys Services - Water - Food - Income Dis-services - Diseases (malaria, bilharzia) - Exposure to agro- chemicals
  8. 8. Land use change and disease transmission 1 10 100 1000 10000 Aedes spp Anopheles spp Culex spp Mansonia spp irrigated area non-irrigated area Villages Mosquito species Lognumberofmosquitoes 1 10 100 1000 10000 Aedes spp Anopheles spp Culex spp Mansonia spp irrigated area non-irrigated area Farms Mosquito species Lognumberofmosquitoes 1 10 100 1000 10000 Aedes spp Anopheles spp Culex spp Mansonia spp irrigated area non-irrigated area Villages Mosquito species Lognumberofmosquitoes 1 10 100 1000 10000 Aedes spp Anopheles spp Culex spp Mansonia spp irrigated area non-irrigated area Farms Mosquito species Lognumberofmosquitoes I FallowperiodIrrigationseason Results: Apparent densities of mosquitoes trapped
  9. 9. Variable Levels All mosquitoes trapped Primary RVF vectors Mean SD Credible interval Mean SD Credible interval 2.50% 97.50% 2.50% 97.50% Land use Irrigation 1.23 0.38 0.46 1.94 1.47 0.19 1.10 1.85 Other 0.00 0.00 Rain 0.03 0.00 0.02 0.03 0.03 0.00 0.02 0.03 Hyper-parameters Theta 1 -3.03 1.97 -6.79 0.95 -3.53 3.16 -9.75 2.68 Theta 2 1.87 1.53 -1.23 4.75 2.26 3.16 -3.95 8.46 DIC 1099.57 641.39 Outputs of a regression model used to analyse the effects of rainfall and irrigation on mosquito densities
  10. 10. Analysis of sero-prevalence data from people Variable Level Rift Valley fever sero-prevalence Odds Ratio P> |Z | Estimate 95% CI Fixed effects Gender Male 1.85 1.28 – 2.66 0.00 Female 1.00 Age (years) <9 - 9 - <18 0.10 0.02 – 0.48 0.00 >18 - <30 0.64 0.42 – 0.98 0.04 >30 1.00 Occupation Farmer 0.44 0.21 – 0.92 0.03 Pastoralist 1.00 - Student 0.32 0.05 – 2.03 0.23 Other 0.85 0.47 – 1.54 0.60 Household size <10 1.00 - >10 1.81 1.20 – 2.73 0.01 Site Irrigated 1.77 0.85 – 3.92 0.12 Riverine 1.83 0.85 – 3.92 0.11 Pastoral 1.00 Random effects ICCc: Household | Village Log likelihood -343.87
  11. 11. Discussion • Irrigation – increased food production but more habitat fragmentation and less biodiversity • Primary vectors of RVF found in drainage canals. This implies increased risk of RVF • Seri-prevalence in livestock and people– higher in irrigated area but not significant. Surveillance for active infections required • To manage vector-borne diseases -- better irrigation technologies instead of flood irrigation should be considered
  12. 12. This work, Dynamic Drivers of Disease in Africa Consortium, NERC project number NE-J001570-1, was funded with support from the Ecosystem Services for Poverty Alleviation (ESPA) programme. The ESPA programme is funded by the Department for International Development (DFID), the Economic and Social Research Council (ESRC) and the Natural Environment Research Council (NERC).

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