Egocentric characterisation of the swine trade network in Cambodia and implications for disease surveillance and control

Abstract

Across Southeast Asia, enhanced characterisation of pig value chains is needed to understand disease risk pathways and inform control and surveillance strategies. This study defined a typology of value chain actors in Cambodia and characterised their individual, ‘egocentric’, swine trade networks. Questionnaire-based cross-sectional surveys were conducted between May 2020 and April 2022 in four south-central provinces, sampling ‘egos’ via a multi-stage cluster design. We describe networks of 376 egos involving 4705 trade partners (‘alters’) and 669,363 pigs over six months. Five producer types were identified: company-affiliated large breeding (n = 21) and growing farms (n = 68), independent breeding- (n = 104) and growing-oriented smallholders (n = 77), and boar service providers (BSP; n = 19). Three pig-exchanger types were also identified: ‘traders’ (n = 11), ‘middlemen’ (n = 12), and ‘butchers’ (n = 51). Network analysis revealed BSP, middlemen, and large breeding farms as ‘brokers’ with many in- and outgoing trade links with producers, increasing their potential for pathogen introduction and onward transmission. Logistic regression supported this risk-profiling: compared to breeding-oriented smallholders, BSP had 8.1 times greater odds (95 % CI: 2.4–27.8) of high pig mortality risk (≥5 % of herd size), while large breeding farms had 6.0 times greater odds (95 % CI: 2.0–18.6) than large growing farms. Large breeding farms supplied pigs to all producer types including smallholders and BSPs (1 % of their aggregate supply), underscoring their dissemination potential. Middlemen and BSP connected otherwise weakly connected smallholders, highlighting opportunities for targeted disease-control. Slaughterhouses acted as network ‘sinks’, receiving pigs from smallholders and farms associated with different companies, making them key targets for disease surveillance. Large farms transported pigs the furthest distances (median >40 km; max >120 km) while smallholders mostly traded pigs locally (median <5 km; max 114 km). This study demonstrates the value of egocentric sampling for livestock network characterisation and contributes to the limited knowledgebase on swine trade networks in Southeast Asia.