Evaluation of Pathogenetic and Immunological Properties of a Vietnamese Isolate of Porcine Reproductive and Respiratory Syndrome Virus of Vietnam in Experimentally Infected Piglets

This study aimed to evaluate the pathogenic potential of the 2024 Vietnam PRRSV genotype 2 (NA01/2024, isolate). Fifteen 6-week-old piglets were intramuscularly inoculated with 1 × 10^5.5 TCID₅₀/mL of PRRSV, while fifteen control piglets remained uninfected. Blood and nasal swabs were collected every 3 days until 21 days post-infection (dpi). Necropsies were performed on piglets at 6, 15, and 21 dpi. Infected piglets exhibited fever, blue ear, weight loss, respiratory distress, diarrhea, and leucopenia between 3 and 12 dpi. PRRSV was detected in serum and nasal secretions up to 21 dpi, peaking between 6 and 9 dpi. Seroconversion began at 6 dpi, with the highest antibody titers at 21 dpi. Virus load was highest in lung tissues at all intervals, while the spleen and lymph nodes showed higher viral load at later stages. Routine blood tests indicated a slight decrease in red blood cells, hemoglobin, and reticulocytes, along with a notable increase in monocytes in infected piglets. Cytokine levels (IFN-γ, IL-6, and IL-10) in serum and lung tissues were significantly higher in infected piglets compared to controls. Additionally, the PRRSV infection triggered innate immune responses, including cytokines, growth factors, and chemokines in whole blood and tissues such as IFN-α, IFN-β, TNF-α, IL-1β, etc. These findings highlight the pathogenicity of the Vietnam PRRSV NA01/2024 isolate and its impact on the immune response, providing insights into PRRSV infection mechanisms and strategies for prevention and control.