Understanding the spread of African swine fever in Nepal: spatiotemporal analysis of early-phase outbreaks, March 2022–July 2024

Abstract

Abstract African swine fever (ASF) is a highly contagious disease of pigs that poses a significant threat to food security, economies, and livelihoods. In Nepal, where pig farming is an important livelihood of many vulnerable ethnic communities, ASF was first reported on 19 March 2022 and has since spread across the country. This study aimed to characterize the spatiotemporal patterns of ASF outbreaks in Nepal, identify high-risk clusters, and assess their associations with environmental factors to inform targeted ASF control and prevention. A retrospective analysis of confirmed ASF outbreaks reported from March 2022 to July 2024 was conducted. Temporal trends and seasonal patterns were analyzed, while spatial clustering was assessed using SaTScan. Associations between outbreaks and environmental variables (rainfall, temperature, dewpoint temperature, and relative humidity) were examined. A total of 43 outbreaks were reported across 21 of 77 districts in Nepal, including 42 in domestic pigs and one in wild boars. Most outbreaks (77%) were reported in 2022, with a peak during the summer months. Outbreaks were reported in all seven provinces, with Bagamati Province having the highest number of outbreaks (18/43). ASF outbreaks mostly occurred in small- and medium-scale holdings (36/42), while commercial farms were also affected. A significant cluster was identified in Sudurpaschim Province. Rainfall was significantly associated with outbreak occurrence ( p = 0.0118). This study provides the first evidence on the spatiotemporal dynamics of ASF during the early phase of outbreaks in Nepal, supporting risk-based surveillance and targeted interventions to strengthen ASF prevention and control.