Spatiotemporal Drivers of the African Swine Fever Epidemic in Lao PDR

Abstract

African swine fever (ASF) is a devastating transboundary disease of swine. Following the first report of ASF in China in August 2018, ASF spread through South-East Asian nations in 2019. Without control and containment measures, ASF can decimate smallholder pig holdings and disrupt value chains. This study aimed to describe the spatiotemporal spread of the 2019 Lao PDR ASF epidemic in domestic pigs, identify environmental (protected areas and forests), production (pig ownership), transportation (roads), and social (poverty and ethnicity) risk factors, and recommend measures that could reduce ASF spread. A retrospective spatiotemporal study was conducted at the village level. Information on the date that ASF was first reported from each case location was collected, and the outcome variable of interest “epidemic day” was created. Risk factor information from different sources was extracted for each case location. The association or correlation between epidemic day and risk factors for the spread of ASF was investigated using Kruskal–Wallis tests and Spearman rank correlation statistics. The epidemic started on June 16 and lasted for 190 days, displaying a right-skewed epidemic curve. The directional distribution was rotated approximately 305°, from Southeast to Northwest Laos. Significant risk factors for ASF associated with epidemic day were location in terms of distance from the closest protected natural area $\left(P=0.020\right)$ , pig ownership $\left(P=0.005\right)$ , road networks $\left(P=0.003\right)$ , and poverty indices $\left(P<0.001\right)$ . Cases were reported earlier in this epidemic at locations that were closer to protected natural areas, of higher pig ownership, more connected via the national road network, and which experienced elevated poverty. The spatiotemporal pattern described suggests that ASF was introduced via infected pigs from Vietnam. Based on study findings, recommendations for smallholder pig production in Southeast Asia include improving knowledge of swine value chains to inform disease risk and control, monitoring pig transportation, implementing stricter biosecurity measures on the domestic pig population, and providing biosecurity support and education to smallholder pig farmers in poverty.