Does irrigated urban agriculture influence the transmission of malaria in the city of Kumasi, Ghana?

Abstract

To verify the possible impact of irrigated urban agriculture on malaria transmission in cities, we studied entomological parameters, self-reported malaria episodes, and household-level data in the city of Kumasi, Ghana. A comparison was made between city locations without irrigated agriculture, city locations with irrigated urban vegetable production, and peri-urban (PU) locations with rain-fed agriculture. In the rainy as well as dry seasons, larvae of Anopheles spp. were identified in the irrigation systems of the urban farms. Night catches revealed significantly higher adult anopheline densities in peri-urban and urban agricultural locations compared to non-agricultural urban locations. Polymerase chain reaction (PCR) analysis of Anopheles gambiae sensu lato revealed that all specimens processed were A. gambiae sensu stricto. The pattern observed in the night catches was consistent with household interviews because significantly more episodes of malaria and subsequent days lost due to illness were reported in peri-urban and urban agricultural locations than in non-agricultural urban locations. In Kumasi, urban agriculture is mainly practised in inland valleys, which might naturally produce more mosquitoes. Therefore more detailed studies, also in other cities with different water sources and irrigation systems, and a better spatial distribution of sites with and without urban agriculture than in Kumasi are needed.