impact of the koka reservoir on malaria

Solomon Kibret, Matthew McCartney and Jonathan Lautze

Impact of the Koka Reservoir on Malaria

Challenge Program on Water and Food, 2nd International Forum on Water and Food, Addis Ababa, Ethiopia

November 2008Cover slide photo credit: Solomon Kibret (Koka reservoir), Jonathan Lautze

Introduction

• Investment in hydraulic infrastructure, including large dams, is crucial for economic growth and poverty reduction in many parts of sub-Saharan Africa.

• Dams are built to cope with climate variability and may help to mitigate climate change.

• Inadequate consideration of both environmental and public health impacts can seriously undermine the benefits to be gained from such investments.

• Key among the potential negative effects of large dams is intensified malaria transmission, resulting from changes in environmental conditions.

• Several large dams are currently being built in Ethiopia

• Research is required to understand the link between reservoirs and malaria transmission in the different hydro-climatic conditions

• characterize mosquitoes breeding habitat associated with Koka dam and reservoir shoreline

• compare vector density in villages at close proximity to the reservoir with those further away.

• compare malaria incidence in villages at close proximity to the reservoir with those further away.

• correlate water level changes over a period of time with the abundance and maturity of Anopheles larvae in shoreline sites and malaria transmission surrounding the Koka reservoir.

Objectives of the study

The study area

Source: Kibret, S.; McCartney, Matthew; Lautze, Jonathan; Jayasinghe, G. 2009. Malaria transmission in the vicinity of impounded water: evidence from the Koka Reservoir, Ethiopia. Colombo, Sri Lanka: International Water Management Institute (IWMI). 39p. (IWMI Research Report 132)

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Mean monthly rainfall Mean Daily Maximum Temperature

Mean Daily Minimum Temperature

Climate

Malaria is seasonally demarcated, with peak transmission following the long wet season, generally lasting from mid-September to mid-November.

Source: Created by S.Kibret using IWMI data, 2008

Epidemiological survey:

Records of malaria diagnoses were obtained for all kebeles (i.e. a total of 22

kebeles) located within 10 km of the reservoir for the period October 1994 to

August 2002.

These data were obtained from three malaria control centers located close to

the reservoir: Adama, Mojo and Alem Tena.

malaria case-rates (malaria diagnoses per 1000 person-month) for each kebele

was generated.

Materials and Methods

Entomological survey: Four villages selected

Ejersa, Siree-Robe (<1 km from the reservoir) = Reservoir Villages Kuma and Gudedo (> 6km from the reservoir) = Control Villages

both larval and adult mosquitoes were collected fortnightly in the four study

villages for 16-months (between August 2006 and December 2007)

Potential mosquito breeding habitats in the study area included:

• seepage at the base of the dam, • reservoir shoreline puddles, • man-made pools, • agricultural field puddles • rain puddles

Materials and Methods…..

Ph

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: J

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autz

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Photo Credit: Jonathan Lautze

Photo Credit: Jonathan Lautze

29.6-40.234.96-9

46.8-63.655.23-6

69.6-92.280.90-3

95% CIAnnual cases per

1000 personsDistance from reservoir (km)

Malaria cases passively reported in terms of proximity to the Koka Reservoir.

Results

Impact of the reservoir on malaria incidence

Source: Preliminary figures compiled for Research report 132, S.Kibret

Results…...

Seasonal distribution of malaria cases:

Oct-DecJul-SepApr-JunJan-Mar

Case

s/1000 p

ers

on-m

onth

s

12

10

8

6

4

2

0

Km to re servoir

<3

3-6

6-9

• The reservoir’s main impact on malaria transmission is during and after the rainy season.

Source: Lautze, J et al.. 2007. Effect of a large dam on malaria risk: The Koka Reservoir in Ethiopia. Tropical Medicine and International Health, 12(8):982-989

Results…...

Species of malaria:

the proportion of P. falciparum infections is greater in communities located close to the reservoir.

45.43,56454.24,2577,8526-9

38.62,56061.34,0696,6373-6

34.11,66065.83,2024,8630-3

%No.%No.

P. vivaxP. falciparum Total

Plasmodium cases

Distance from

reservoir (km)

Source: Lautze, J et al.. 2007. Effect of a large dam on malaria risk: The Koka Reservoir in Ethiopia. Tropical Medicine and International

Health, 12(8):982-989

Results…...

Impact of the reservoir on vector abundance

Larval abundance in reservoir and control villages Aug 2006 – Dec 2007.

3.1 – 16.59.80.5 – 4.12.3Control Villages

< 0.000119.8 – 46.433.1<0.00019.3 – 21.115.2Reservoir Villages

p-value 95% CIMean larval density

p-value95% CIMean number of positive larval sites

• Overall, approximately 7-times more positive larval sites and 3-times higher larval density in the reservoir villages than in the control villages


Results…...

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Jan-Mar Apr-Jun Jul-Sep Oct-Dec

Mea

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larv

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dips

Siree-Robe (reservoir village)

Ejersa (reservoir village)

Kuma (control village)

Gudedo (control village)

Seasonal Anopheles larval density in the reservoir and control villages.

Source: Preliminary figures created for Research Report 132, S. Kibret

Results…...

Summary of adult Anopheles mosquitoes collected August 2006 and December 2007.

4380 (0.0)68 (15.5)92 (21.0)278 (63.5)Control Villages

251429 (1.2)342 (13.6)787 (31.3)1356 (53.9)Reservoir Villages

TotalAn. funestusAn. coustaniAn. pharoensisAn. arabiensis


Results…...

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ean

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An. arabiensis (Reservoir villages)

An. pharoensis (Reservoir villages)

An. arabiensis (Control villages)

An. pharoensis (Control village)

Density of An. arabiensis and An. pharoensis between August 2006 and December 2007

Source: Preliminary figures created for Research Report 132, S. Kibret

Results…...

319 238 (74.6) 69 (21.6) 31 (9.7) 385 240 (62.3) 111 (28.8) 72 (18.7) 103 44 (42.7) 63 (61.2) 16 (15.5) 8 2 (25.0) 4 (50.0) 3 (37.5) 136 85 (62.5) 41 (30.1) 29 (21.3) 45 26 (57.8) 15 (33.3) 8 (17.8) 23 5 (21.7) 13 (56.5) 6 (26.1) 0 0 0 0

Reservoir An. arabiensis An. pharoensis An. coustani An. funestusControl An. arabiensis An. pharoensis An. coustani An. funestus

No. tested No. positive No. positive Unidentified for HB for BB

Village Species

Bloodmeal sources of Anopheles mosquitoes, Aug 2006–Dec 2007


Results…...

824 0.97 574 0.70 252 0.00 20 0.00

532 1.32 213 0.47 90 0.00 9 0.00

161 0.00 42 0.00 45 0.00 0 0

117 0.00 50 0.00 23 0.00 0 0

Ejersa

Siree-Robe

Gudedo

Kuma

An. arabiensis An. pharoensis An. coustani An. funestus

no. tested positive (%) no. tested positive (%) no. tested positive (%) no. tested positive(%)Village

Plasmodium falciparum sporozoite rates between August 2006 and December 2007


• Dam has increased malaria incidence in the villages in close proximity to the reservoir

• Reservoir significantly increases breeding habitat for malaria vectors

• Outdoor questing of mosquitoes in the early evening may limit the effectiveness of current malaria control strategies (i.e. ITN*)

• Requires further investigation but preliminary results indicate that reservoir management (i.e. manipulation of water-levels) can impact vector abundance and malaria transmission

Conclusions

*ITN: Insect Treated Net

Related Publications

• Kibret, S., McCartney, M., Lautze, J, Jayasinghe, G. 2009. Malaria Transmission in the vicinity of impounded water: Evidence from the Koka Reservoir, Ethiopia. Colombo, Sri Lanka: International Water Management Institute. Research Report 132.

• Lautze, J., and Kirshen, P. September, 2007. Dams, Health, and Livelihoods: Lessons from the Senegal, Suggestions for Africa. International Journal of River Basin Management 5(3).

• Lautze, J., McCartney, M., Kirshen, P., Olana, D., Jayasinghe, G., and Spielman, A. 2007. The Effect of a Large Dam on Malaria Risk: The Koka Reservoir, Ethiopia. Tropical Medicine and International Health 12(8): 982-989.

THANK YOU!!

For complete publication please visit:http://www.iwmi.cgiar.org/Publications/IWMI_Research_Reports/PDF/PUB132/RR132.pdf

(2009)

N.B :Some of the data used in this presentation was based on preliminary results (2008)

impact of the koka reservoir on malaria

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