African swine fever dynamics in Vietnam from 2022 to 2023 : genetic diversity and vaccine implications

Abstract

African swine fever (ASF) has profoundly impacted the swine industry in Vietnam, where the disease has transitioned from epidemic to endemicity. Despite extensive control efforts, important knowledge gaps remain regarding the molecular profile of ASF virus (ASFV) during the endemic phase (2022 – 2023) and the impact of the ASF epidemic on other swine pathogen genetic pools. This study investigated the molecular epidemiology of ASFV and porcine reproductive and respiratory syndrome virus type 2 (PRRSV-2) in Vietnam. The results demonstrate that ASFV vaccine-like variants can spill into unvaccinated breeding herds and cause atypical clinical manifestations, highlighting the epidemiological importance of vaccine-associated viruses under field conditions. Although ASFV genotype II has remained predominance during the endemic phase, both vaccine-like and wild-type viruses continue to diversify through localized mutations and structural genomic variations. In contrast, the ASF epidemic substantially reshaped the genetic landscape of PRRSV-2, increasing lineage diversity while exerting minimal influence on the evolutionary rate of the endemic sub-lineage L8E, and leading to the identification of two newly established sub-lineages, L1M and L10B, in Vietnam. Collectively, these observations demonstrate that ecological changes associated with ASF outbreaks and subsequent disease control interventions have influenced the evolutionary trajectories of major swine pathogens. Our findings advance understanding of the molecular epidemiology and evolutionary dynamics of ASFV and PRRSV-2, provide scientific evidence to support the integration of genomic surveillance, standardized molecular characterization, routine disease monitoring, vaccine management, and evidence-based strategies for the sustainable prevention and control of transboundary swine diseases in Vietnam and across Southeast Asia.