Establishment of a Duplex Quantitative PCR Assay for the Detection and Differentiation of African Swine Fever Virus Genotype I, Genotype II, and Genotype I/II Recombinants

African swine fever (ASF) is a highly fatal, febrile infectious disease of domestic pigs and wild boars caused by the African swine fever virus (ASFV). Recently, highly virulent recombinant ASFVs with chimeric genomes derived from p72 genotype I and II viruses have emerged in China, Vietnam, and Russia. These genotype I/II recombinants can evade immunity induced by genotype II–based vaccines, thereby complicating disease control efforts. To address this challenge, a novel duplex quantitative PCR (qPCR) assay was developed to simultaneously detect and differentiate genotypes I, II, and I/II recombinants in a single reaction. The assay exhibited high sensitivity and specificity, with a reliable detection limit of 10 copies/reaction for genotype I and II ASFV DNA. Validation using clinical samples collected in northern Vietnam in 2025 confirmed a robust performance in accurately distinguishing circulating genotype II viruses from recombinant genotype I/II viruses, including the detection of potential co-infection. Whole-genome sequencing of selected positive samples further corroborated these findings. Overall, this qPCR assay provides a precise and efficient tool for identifying currently circulating ASFV genotypes, thereby facilitating improved disease surveillance and supporting a comprehensive understanding of the evolving epidemiological landscape of ASF in regions with increasing viral genetic diversity.