Brefeldin A inhibits duck plague virus replication by impairing virion envelopment

Duck plague virus (DPV) is the causative agent of duck plague (DP), an acute and highly fatal disease that inflicts substantial economic losses in the waterfowl industry. The virus acquires its envelope from the endoplasmic reticulum (ER) and Golgi apparatus during virion assembly. Currently, there are no specific antiviral drugs available, making the development of novel anti-DPV drugs critically important. Brefeldin A (BFA) is an antibiotic known to disrupt endoplasmic reticulum-Golgi transport and inhibit the replication of various enveloped viruses. However, its inhibitory effect and mechanism on DPV infection remain unclear. Our study demonstrates that BFA effectively inhibits DPV replication in duck embryo fibroblast (DEF) cells in a concentration-dependent manner. Time-addition and antiviral duration analysis revealed that BFA mainly exerts therapeutic inhibitory effects after viral infection, and its effect is most significant within 48 hours after infection. Further investigation indicated that BFA does not affect the classical stages of the DPV life cycle, including viral adsorption, endocytosis, genome replication, or release. Instead, it significantly suppresses direct cell-to-cell spread. Mechanistic studies showed that BFA disrupts the normal subcellular localization and punctate distribution of the viral tegument protein UL51 and the envelope glycoprotein gC (encoded by UL44), causing their dispersion throughout the cytoplasm. Transmission electron microscopy (TEM) further confirmed that BFA leads to the accumulation of numerous DPV nucleocapsids in the nucleus, with unenveloped viral particles observed at the nuclear membrane. Meanwhile, the number of mature, enveloped virions in the cytoplasm was markedly reduced. In conclusion, BFA can significantly inhibit the replication of DPV in DEF cells and is a potent antiviral drug targeting DPV.