Small scale irrigation and malaria in Ziway, Ethiopia
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Ecohealth Forum 2Dec08
Eline Boelee, Solomon Kibret, Beyene Petros, Yihenew Alemu
EcoHealth ForumMerida, Mexico
2 December 2008
Small scale irrigation and malaria in Ziway, Ethiopia
Ecohealth Forum 2Dec08
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)
Ecohealth Forum 2Dec08
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?
Ecohealth Forum 2Dec08
Study area - 1
Source: S.Kibret, 2008
Ecohealth Forum 2Dec08
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
Ecohealth Forum 2Dec08
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
Ecohealth Forum 2Dec08
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
Ecohealth Forum 2Dec08
Results - epidemiology
• Higher transmission in village with irrigation, especially in dry season
• P. falciparum main parasite• Income, type of house, malaria
history significant variables
Abene Girmamo(irrigation)
Woshgulla(rain-fed)
N Positive (%) N Positive (%)
Wet season 699 112 (16.0) 692 136 (19.6)
Dry season 528 120 (22.7) 516 59 (11.4)
Overall 1227 232 (18.9) 1208 195 (16.1)
negative82%
P. falciparum13%
P. vivax5%
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
Ecohealth Forum 2Dec08
Results – mosquito larvae
• An. pharoensis most prevalent• Higher mosquito densities in more breeding sites
in irrigated area (80% in irrigation habitats)
0
50
100
150
200
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Brick-makingpits (n=5)
Canalleakage
pools (n=12)
Irrigated fieldpuddles(n=23)
Irrigationcanals (n=4)
Rain pools(n=7)
Brick-makingpits (n=7)
Rain pools(n=4)
Waterharvestingpools (n=1)
Abene Girmamo (irrigation) Woshgulla (rain-fed)
An. arabiensis
An. pharoensis
An. coustani
Source: Graph created by E.Boelee based on data from S.Kibret, 2008
Photo Credit: Solomon Kibret
Ecohealth Forum 2Dec08
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
An. arabiensis An. pharoensis An. coustani
Abene Girmamo (irrigation)
Wet season 182 340 76
Dry season 309 212 94
Overall 491 552 170
Woshgulla (rain-fed)
Wet season 0 0 0
Dry season 38 4 16
Overall 38 4 16Source: S.Kibret, 2008
Ecohealth Forum 2Dec08
Results – biting peaks
0.0
10.0
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1800-1
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700
Indoors (n = 24 light trap-nights)
Outdoors (n = 24 light trap-nights)
An. arabiensis
An. pharoensis
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1800-1900
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0500-0600
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Indoors (n = 24 light trap-nights)
Outdoors (n = 24 light trap-nights)
An. coustani
0.0
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-190
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Hour
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rce
nta
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of
mo
sq
uit
oe
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co
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cte
d e
ac
h h
ou
r
Indoors (n = 24 light trap-nights)Outdoors (n = 24 light trap-nights)
Source: S.Kibret, 2008
Ecohealth Forum 2Dec08
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
An. arabiensis An. pharoensis An. coustani
N value N value N Value
HBI 120 0.78 142 0.69 16 0.06
SR 424 1.18% 509 0.59% 131 0Source: S.Kibret, 2008
Ecohealth Forum 2Dec08
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
Ecohealth Forum 2Dec08
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
Ecohealth Forum 2Dec08
Thank youThank you
More info: e.boelee@cgiar.org
http://www.iwmi.cgiar.org/Publications/index.aspx
http://www.doi.org/10.1111/j.1365-3156.2009.02423.x
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