Socioeconomic and ecological drivers of contagious pig diseases in free-range systems: Evidence from Gwembe Valley, Zambia

Abstract

Free-range pig systems support rural livelihoods in Zambia but increase exposure to contagious diseases through unrestricted movement, environmental contamination, and informal trade. We explored non-biological drivers of disease risk in Gwembe District to inform practical control strategies. We used Spatial Group Model Building (SGMB) with LayerStack mapping to engage 12 purposively selected value-chain actors (farmers, traders, transporters, and veterinary personnel). Participants co-produced spatial layers (settlements, production zones, markets, disease occurrence, service points), behavior-over-time graphs, and causal loop diagrams (CLD). Findings highlighted intersecting non-biological drivers: free-range husbandry, open defecation and shallow-well contamination, seasonal water scarcity, limited veterinary access, informal marketing, and economic pressures that shape herd management and pig movement. Discrepancies between transporters' reported volumes and district records suggested unreported flows that could undermine surveillance. Participants recognized risks consistent with African swine fever (ASF) spread via pig movement and porcine cysticercosis (PCC) via sanitation failures, but awareness of PCC pathways was limited. Disease dynamics in free-range systems arise from feedback across human practices, animal behavior, environment conditions, within markets interactions acting as key transmission paths that shape both local persistence and wider disease spread. Low-cost housing, community sanitation, participatory surveillance, and tailored farmer education are feasible entry points for improving disease prevention and control in free-range pig production systems. In Gwembe valley, SGMB effectively elicited local knowledge and revealed leverage points for integrated One Health interventions that align with community realities and can strengthen rural livelihoods. Disease dynamics in free-range systems arise from feedback across human practices, animal behavior, and environmental conditions, with market interactions acting as key transmission nodes that shape both local persistence and wider disease spread.