Evaluation of Pathogenetic and Immunological Parameters of the Genotype I and II Recombinant African Swine Fever Viruses Detected in Pigs in Vietnam.

Recombinant genotype I-II African swine fever virus (ASFV) strains with high virulence have been increasingly reported in China and Vietnam since 2023, raising significant concerns for disease control. In this study, we characterized the hematological, virological, pathological, and immunological dynamics in ASFV-inoculated pigs, with particular emphasis on temporal changes associated with mortality following the onset of viremia. Specific-pathogen-free pigs were intramuscularly inoculated with 1 × 103 or 1 × 105 HAD50/mL of ASFV LS100 virus strain and developed acute disease characterized by high fever and severe hemorrhagic manifestations. The incubation period ranged from 3 to 5 days, with mortality occurring between 6 and 10 days post-inoculation (dpi). Viral genomic DNA was detected in blood, oral swabs, and rectal swabs as early as 2-4 dpi. Pathological examination revealed prominent necrotic skin lesions and joint swelling. Although hematological parameters and serum biochemical profiles were comparable between high- and low-dose groups, differences in viral load distribution were observed. Notably, cytokine profiling in whole blood revealed a strong and persistent upregulation of pro-inflammatory mediators, including IL-1β, IL-6, IL-12p40, TNF-α, IFN-γ, CCL2, CCL3, CCL14, CXCL9, and CXCL10, which correlated with persistent fever from 2 to 7 dpi. Collectively, these findings confirm that naturally occurring recombinant genotype I-II ASFV strains are highly virulent and capable of inducing severe systemic inflammation. Their continued circulation poses substantial challenges for ASF control and prevention in Vietnam and threatens the global swine industry.