Abstract
BackgroundIrrigation schemes have been blamed for the increase in malaria in many parts of sub-Saharan Africa. However, proper water management could help mitigate malaria around irrigation schemes in this region. This study investigates the link between irrigation and malaria in Central Ethiopia.MethodsLarval and adult mosquitoes were collected fortnightly between November 2009 and October 2010 from two irrigated and two non-irrigated (control) villages in the Ziway area, Central Ethiopia. Daily canal water releases were recorded during the study period and bi-weekly correlation analysis was done to determine relationships between canal water releases and larval/adult vector densities. Blood meal sources (bovine vs human) and malaria sporozoite infection were tested using enzyme-linked immunosorbent assay (ELISA). Monthly malaria data were also collected from central health centre of the study villages.ResultsMonthly malaria incidence was over six-fold higher in the irrigated villages than the non-irrigated villages. The number of anopheline breeding habitats was 3.6 times higher in the irrigated villages than the non-irrigated villages and the most common Anopheles mosquito breeding habitats were waterlogged field puddles, leakage pools from irrigation canals and poorly functioning irrigation canals. Larval and adult anopheline densities were seven- and nine-fold higher in the irrigated villages than in the non-irrigated villages, respectively, during the study period. Anopheles arabiensis was the predominant species in the study area. Plasmodium falciparum sporozoite rates of An. arabiensis and Anopheles pharoensis were significantly higher in the irrigated villages than the non-irrigated villages. The annual entomological inoculation rate (EIR) calculated for the irrigated and non-irrigated villages were 34.8 and 0.25 P. falciparum infective bites per person per year, respectively. A strong positive correlation was found between bi-weekly anopheline larval density and canal water releases. Similarly, there was a strong positive correlation between bi-weekly vector density and canal water releases lagged by two weeks. Furthermore, monthly malaria incidence was strongly correlated with monthly vector density lagged by a month in the irrigated villages.ConclusionThe present study revealed that the irrigation schemes resulted in intensified malaria transmission due to poor canal water management. Proper canal water management could reduce vector abundance and malaria transmission in the irrigated villages.
Highlights
Irrigation schemes have been blamed for the increase in malaria in many parts of sub-Saharan Africa
The present study aims to assess the relationship between irrigation practices and malaria transmission and evaluate water management options to mitigate malaria transmission around irrigation schemes in Central Ethiopia
The present study indicated that the small-scale irrigation schemes of Central Ethiopia resulted in increased malaria transmission in communities living in the irrigated villages throughout most of the year
Summary
Irrigation schemes have been blamed for the increase in malaria in many parts of sub-Saharan Africa. The region is long known for malnutrition and it has been predicted that climate change threatens to increase malnutrition in the region by 14 million by 2020, with staple food production in many sub-Saharan countries falling by more than 25% [2] Alarmed by these threats, several large- and small-scale irrigation schemes are under construction across the region with the goal of ensuring food security and alleviating poverty [3]. Development of irrigation schemes in sub-Saharan Africa has been blamed for the increase of malaria risk through creating favourable breeding sites for malaria vector mosquitoes [5,6,7,8,9]. Water resources development brings opportunities of cost-effective vector control measures through proper water management to create conditions less favourable for mosquito vector breeding [10,11,12,13,14]
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