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.