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Impact of Small-scale Irrigation on Malaria Transmission in Ziway, Ethiopia

Study evaluating the impact of irrigation on malaria transmission in Central Ethiopia. Results show higher transmission and mosquito densities in irrigated areas. Recommendations include environmental water management. More info: e.boelee@cgiar.org

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Impact of Small-scale Irrigation on Malaria Transmission in Ziway, Ethiopia

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  1. Small scale irrigation and malaria in Ziway, Ethiopia Eline Boelee, Solomon Kibret, Beyene Petros, Yihenew Alemu EcoHealth Forum Merida, Mexico 2 December 2008

  2. Partners and funding • Part of Austria-funded research project on impacts of irrigation on poverty and environment in Ethiopia • Study based on 2 MSc theses, Biology Department, Addis Ababa University • Co-funded by CGIAR Systemwide Initiative on Malaria and Agriculture (SIMA)

  3. Set-up of the study • Objective: evaluate the impact of a small-scale irrigation scheme in Central Ethiopia on malaria transmission • Classic biomedical approach • MSc Epidemiology: parasitological survey and socio-economic questionnaire • MSc Entomology: adult and larval sampling, ELISA tests • Would we have gotten other results using EcoHealth approach?

  4. Study area - 1 Source: S.Kibret, 2008

  5. Study area - 2 • Ziway in Central Rift Valley • P = 700-800 mm, bimodal; mean T = 20 °C • heavy rains in June - September • short rains in April and May • Seasonal malaria transmission (unstable) • Peak transmission September – November • Second minor transmission April / May • Plasmodium falciparum accounts for 60-70% of malaria cases, vivax malaria less prevalent • Anopheles arabiensis is primary vector, An. pharoensis secondary

  6. Study area - 3 • Two villages • Altitude around 1650 m • Subsistence farming • Livestock important, often indoors at night • Abene Girmamo – irrigation • Population size 950 • Human / Livestock ration 1: 0.4 • Onion, cabbage, tomato and maize • Woshgulla – no irrigation • Population size 741 • Human / Livestock ration 1: 0.6

  7. Sampling methods • Epidemiology • Thick & thin blood smears (finger prick) by technicians • Transmission season September/October 2005 • Dry season January/February 2006 • Questionnaire • Household, farm size, income, agricultural system, livestock, housing • Entomology • Larval and adult mosquito sampling • Dry season January/February 2006 • Short rainy season April/May 2006 • Larvae: standard 350 ml dipper • Adults: CDC light traps, aspirator, spray catches, ELISA tests

  8. Results - epidemiology • Higher transmission in village with irrigation, especially in dry season • P. falciparum main parasite • Income, type of house, malaria history significant variables Source: Table compiled by E.Boelee based on data from Y.Alemu,2007 Source: Pie-chart created by E.Boelee based on data from Y.Alemu,2007

  9. Results – mosquito larvae • An. pharoensis most prevalent • Higher mosquito densities in more breeding sites in irrigated area (80% in irrigation habitats) Source: Graph created by E.Boelee based on data from S.Kibret, 2008 Photo Credit: Solomon Kibret

  10. Results – adult mosquitoes • Higher mosquito densities in village with irrigation • Higher densities in dry season • An. pharoensis and An. coustani more outdoors • An. arabiensis more indoors Source: S.Kibret, 2008

  11. Results – biting peaks An. arabiensis An. pharoensis An. coustani Source: S.Kibret, 2008

  12. Results – HBI & SR • Human Blood Index (HBI) determined for Abene Girmamo (irrigation) village only • No mosquitoes tested positive in rain-fed village and none positive for P. vivax • Higher sporozoite rates in short rainly season • An. arabiensis and An. pharoensis most important anthropophagic vector species Source: S.Kibret, 2008

  13. Discussion and Conclusions • Irrigation system provides breeding sites for year-round and increased transmission of malaria in Ziway area, Ethiopia • An. arabiensis and An. pharoensis most important anthropophagic vector species, breeding all year • Higher infection rates among irrigating farmers possibly caused by evening outdoor work • Vector breeding sites associated with poorly maintained canals and hydraulic structures • Trend of earlier biting peak An. arabiensis confirmed – risky for children and adults

  14. Recommendations • Additional studies to capture seasonal and spatial differences • With early biting peaks, alternatives to bed nets required • Environmental water management for source reduction • What could EcoHealth approach bring as added value? Photo Credit: Solomon Kibret

  15. More info: e.boelee@cgiar.org Thank you http://www.iwmi.cgiar.org/Publications/index.aspx http://www.doi.org/10.1111/j.1365-3156.2009.02423.x

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