Repeated Cross-Sectional Surveillance and ORF5-Based Molecular Epidemiology of Porcine Reproductive and Respiratory Syndrome Virus in Anhui Province, China, 2019–2024

Abstract

Simple Summary Porcine reproductive and respiratory syndrome is a major disease of pigs that can cause reproductive failure, breathing problems, poor growth, and substantial economic losses. This study examined how the virus changed over time and across regions of Anhui Province after the African swine fever outbreak. From September 2019 to November 2024, researchers carried out 10 rounds of surveillance at 147 slaughterhouses and 21 facilities that process dead pigs. In total, 18,733 tissue samples were tested for viral genetic material. No positive samples were found in autumn 2020 or spring 2021, but the virus was detected again from autumn 2021 onward and then fluctuated over time. Detection levels were generally higher in northern Anhui, and the overall difference among the three regions was statistically significant. Samples from dead pigs were more likely to contain the virus than samples from slaughter pigs. Comparison of the genetic material from 24 virus samples showed that several distinct virus groups were circulating at the same time, with newer groups becoming more common after 2021. These findings support continued surveillance across farms, slaughterhouses, and rendering plants, together with broader genetic testing and improved evaluation of whether vaccines match locally circulating viruses.