Reconstruction and analysis of the transmission network of African swine fever in People's Republic of China, August 2018-September 2019

Abstract

Introduction of African swine fever (ASF) to China in mid-2018 and subsequent transboundary spread across Asia devastated regional swine production, affecting live pig and pork product-related markets worldwide. In order to explore the spatiotemporal spread of ASF in China, we reconstructed possible ASF transmission networks using nearest neighbour, exponential function, equal probability, and spatiotemporal case-distribution algorithms. From these networks we estimated the reproduction numbers, serial intervals, and transmission distances of the outbreak. The mean serial interval between paired units was around 29 days for all algorithms, while the mean transmission distance ranged from 332-456 kilometres. The reproduction numbers for each algorithm peaked during the first two weeks and steadily declined through the end of 2018 before hovering around the epidemic threshold value of one with sporadic increases during 2019. These results suggest that: 1) swine husbandry practices and production systems that lend themselves to long-range transmission drove ASF spread, and 2) outbreaks went undetected by the surveillance system. China and other affected countries have stepped up efforts to control ASF within their jurisdictions, and continued support for strict implementation of biosecurity standards and improvements to ASF surveillance are essential for halting transmission in China and further spread across Asia.