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

Catherine Besnart Dzombe, Herman Chambaro, Karl Rich, Magda Rich and Chisoni Mumba

PLOS Neglected Tropical Diseases, 2026, vol. 20, issue 7, 1-18

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.Author summary: Free-range pig farming is common in rural Zambia and helps many families earn income and improve food security. However, when pigs roam freely, they can easily come into contact with waste, other animals, and informal markets, which increases the risk of disease spread. Two important diseases in such systems are African swine fever, which kills pigs and affects farmers’ livelihoods, and porcine cysticercosis, which can also infect people and is linked to poor sanitation. We worked with farmers, traders, transporters, and veterinary staff in Gwembe District to understand how everyday practices, environment, and trade patterns influence disease risks. Instead of focusing only on biology, we looked at how non-biological realities shape pig management. Participants showed that poverty, limited veterinary services, seasonal water shortages, and informal pig trade all contribute to disease risk. They also highlighted gaps in disease awareness and reporting. Our findings suggest that improving pig health is not only about medicines. Better sanitation, simple pig housing, farmer education, and community-based surveillance can reduce disease risks while fitting local livelihoods. This study shows that locally informed, participatory approaches can support healthier pigs, safer food, and more resilient rural communities.

Date: 2026
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Persistent link: https://EconPapers.repec.org/RePEc:plo:pntd00:0014523

DOI: 10.1371/journal.pntd.0014523

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