Prophylactic immunomodulation with α-mannan attenuates PRRSV-induced disease in piglets.

PRRSV poses a persistent threat to the global swine industry, yet effective control measures remain limited. This study evaluated the anti-PRRSV effects of α-mannan through in vitro and in vivo experiments. In vitro, α-mannan (25-100 µg/mL) showed no cytotoxicity and did not directly inhibit PRRSV replication. However, it exhibited immunomodulatory activity by inducing IFN-γ expression and suppressing PRRSV-induced elevation of TNF-α and IL-6. In vivo, piglets receiving prophylactic oral α-mannan (50 mg/day for 15 days before and after challenge) showed trends toward reduced PRRSV RNA loads in serum and lung tissue and alleviated pulmonary pathology (based on descriptive observations), shortened duration of detectable PRRSV RNA in oral swabs, delayed fever onset, and all survived to the end of the observation period (15 dpi). In conclusion, prophylactic α-mannan was associated with reduced PRRSV RNA load and attenuated disease severity. These findings suggest α-mannan as a promising candidate for PRRSV control.