Irrigation projects in the Awash Valley and the Gambia province (i.e. canals, micro-dams, rice paddies) expanded breeding sites.
Malarial parasites are becoming increasingly drug-resistant.
Annual harvest and planting time cause labourers to migrate from highlands to lowlands, coinciding with the rainy season and peak transmission period (June-September).
Migrants sleep in the fields overnight, when mosquitoes are active.