Chemical profiling and interferon-mediated antiviral activity of Syzygium aromaticum extract against porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) is highly prevalent in the swine industry and causes substantial economic losses worldwide. Although vaccines are available, their protective efficacy is limited, and effective antiviral therapeutics are lacking, highlighting the urgent need for alternative control strategies. Syzygium aromaticum (SA) is a traditional Chinese herbal medicine with reported biological activities; however, its antiviral potential against PRRSV has not been investigated. Therefore, this study aimed to evaluate the antiviral activity of SA against a genotype 2 PRRSV strain and to characterize its chemical constituents. SA extract inhibited PRRSV infection in a dose-dependent manner in both MARC-145 cells and porcine alveolar macrophages (PAMs). Treatment with SA significantly enhanced type I interferon (IFN-I) production and increased the transcription of interferon-stimulated genes. Chemical profiling showed that saturated fatty acid methyl esters were the predominant volatile constituents of the 50% ethanolic SA extract as identified by gas chromatography–mass spectrometry (GC–MS). In contrast, liquid chromatography–quadrupole time-of-flight tandem mass spectrometry (LC–QTOF–MS/MS) coupled with Global Natural Products Social Molecular Networking (GNPS) revealed that polyphenolic compounds were the major non-volatile components, with miquelianin detected at relatively high abundance. These findings demonstrate that SA extract exhibits antiviral activity against PRRSV, potentially through the enhancement of host innate immune responses. The chemical characterization provides insight into the major constituents of SA extract that may contribute to its antiviral effects. This study suggests that SA may serve as a promising natural antiviral agent or functional feed additive for controlling PRRSV in the swine industry.