Pathological Characteristics of the Emerging Recombinant African Swine Fever Virus Genotypes I and II in Vietnam

African swine fever (ASF) is a highly lethal disease caused by the ASF virus (ASFV) and poses a significant threat to the swine industry worldwide. This study investigated the pathogenicity and pathological characteristics of VNUA/rASFV/HD1/23, a recently identified recombinant ASFV genotype I/II in northern Vietnam. Sixteen healthy, seven-week-old pigs divided into four groups were inoculated intramuscularly (IM) with different virus concentrations (10², 10³, and 10⁴ HAD₅₀/mL), and their clinical signs, survival times, and pathological alterations were evaluated. All experimentally infected pigs exhibited acute clinical signs characterized by fever, anorexia, depression, diarrhea, and death (4–10 days after injection). The pathological findings included splenomegaly with infarcts, hemorrhagic lymph nodes, and severe pulmonary congestion. The pigs that received the highest dose (10⁴ HAD₅₀/mL) IM showed the earliest onset of clinical signs and the shortest survival time. This study provides important insights into the virulence and the pathological lesions induced by the recombinant genotype I/II ASFV strains that emerged in Vietnam.