Landscape Epidemiology of Cassava Brown Streak Disease in the Niger Delta: Modelling Spread and Assessing Containment Options

Cassava Brown Streak Disease (CBSD), caused by Cassava brown streak virus and Ugandan cassava brown streak virus, has expanded westward from East Africa and is now documented in parts of West Africa, representing a phytosanitary emergency for Nigeria's cassava belt. In the Niger Delta, where cassava is the primary food security crop for millions, the potential for CBSD establishment and spread constitutes an existential agricultural risk. This doctoral research develops a landscape epidemiological framework for modelling CBSD spread under Niger Delta agroecological conditions and assessing the feasibility of containment options. The research combines: targeted surveillance across Rivers, Bayelsa, Delta, and Edo States to establish CBSD incidence baselines and determine current disease boundaries; characterisation of Bemisia tabaci vector populations and virus acquisition efficiency for local whitefly biotypes; development of a spatially explicit stochastic spread model incorporating host density, vector movement kernels, and natural landscape barriers; and scenario simulation of containment strategies, including barrier zones, mass roguing, and certified planting material distribution. The theoretical framework introduces an original formulation of landscape connectivity effects on begomovirus spread applicable to fragmented agricultural systems. Model outputs will produce containment resource requirement estimates directly usable by the Nigerian government's plant quarantine authorities. The dissertation makes original contributions to both landscape epidemiology theory and practical CBSD biosecurity planning for West Africa. Keywords: Cassava Brown Streak Disease, landscape epidemiology, Niger Delta, spread modelling, containment.