Abstract
BackgroundDevelopment strategies in Ethiopia have largely focused on the expansion of irrigated agriculture in the last decade to reduce poverty and promote economic growth. However, such irrigation schemes can worsen the socio-economic state by aggravating the problem of mosquito-borne diseases. In this study, the effect of agro-ecosystem practices on malaria prevalence and the risk of malaria transmission by the primary vector mosquito, Anopheles arabiensis, in Ethiopia were investigated.MethodsIn three villages in western Ethiopia practising large-scale sugarcane irrigation, traditional smallholder irrigation and non-irrigated farming, cross-sectional parasitological surveys were conducted during the short rains, after the long rains and during the dry season. Entomological surveys were undertaken monthly (February 2010-January 2011) in each village using light traps, pyrethrum spray collections and artificial pit shelters.ResultsMalaria prevalence and the risk of transmission by An. arabiensis assessed by the average human biting rate, mean sporozoite rate and estimated annual entomological inoculation rate were significantly higher in the irrigated sugarcane agro-ecosystem compared to the traditionally irrigated and non-irrigated agro-ecosystems. The average human biting rate was significantly elevated by two-fold, while the mean sporozoite rate was 2.5-fold higher, and the annual entomological inoculation rate was 4.6 to 5.7-fold higher in the irrigated sugarcane compared to the traditional and non-irrigated agro-ecosystems. Active irrigation clearly affected malaria prevalence by increasing the abundance of host seeking Anopheles mosquitoes year-round and thus increasing the risk of infective bites. The year-round presence of sporozoite-infected vectors due to irrigation practices was found to strengthen the coupling between rainfall and risk of malaria transmission, both on- and off-season.ConclusionThis study demonstrates the negative impact of large-scale irrigation expansion on malaria transmission by increasing the abundance of mosquito vectors and indicates the need for effective vector monitoring and control strategies in the implementation of irrigation projects.
Highlights
Development strategies in Ethiopia have largely focused on the expansion of irrigated agriculture in the last decade to reduce poverty and promote economic growth
Malaria prevalence In the parasitological surveys conducted during the short rainy season, after the long rainy season and during the dry season, a total of 879, 693 and 796 children were examined for malaria parasites in the sugarcane irrigated, the traditional irrigated and the non-irrigated agro-ecosystems, respectively
Plasmodium falciparum and P. vivax were the two parasite species detected during all parasitological surveys in all study villages
Summary
Development strategies in Ethiopia have largely focused on the expansion of irrigated agriculture in the last decade to reduce poverty and promote economic growth. Policy makers emphasize that the increased availability of irrigation and the lowered dependency on rain-fed agriculture is an effective means to increase food production and enhance the self-sufficiency of the rapidly increasing human population [3,4] Despite these socio-economic benefits, irrigation development schemes can aggravate the problem of mosquitoborne diseases by increasing the number of aquatic larval habitats and extending the duration of the transmission season [5,6], or by removing the seasonal cycling all together [7]. The introduction of irrigation schemes, and associated agricultural practices, are considered to be among the primary factors driving the increase in the global malaria burden [7] The mechanisms underlying this phenomenon remain poorly understood given the complexity of vector ecology, parasite transmission and human behaviour
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