Scale drop disease virus enters Asian seabass kidney cells via clathrin-mediated endocytosis in a cholesterol- and dynamin-dependent manner

Scale-drop disease virus (SDDV), a member of the genus Megalocytivirus, family Iridoviridae, causes severe disease outbreaks and significant economic losses in Asian seabass (Lates calcarifer) aquaculture. Despite its importance, the cellular mechanisms underlying SDDV entry into host cells remain poorly understood. In this study, we investigated the endocytic pathways involved in SDDV entry using a highly permissive Asian seabass kidney (ASBK) cell line. Pharmacological inhibition of clathrin-mediated endocytosis using chlorpromazine significantly reduced SDDV infection. In addition, inhibition of dynamin activity impaired viral entry, supporting a requirement for dynamin-dependent vesicle scission during internalization. Consistent with these findings, AP2A1, a core clathrin adaptor protein involved in clathrin-coated vesicle formation, was transiently upregulated during early infection. Cholesterol depletion by methyl-?-cyclodextrin (M?CD) markedly inhibited SDDV entry, whereas cholesterol replenishment restored viral infection, demonstrating a critical role for membrane cholesterol. In contrast, disruption of caveolae-mediated endocytosis or macropinocytosis had no significant effect on viral entry. Together, these results indicate that SDDV entry into ASBK cells occurs predominantly via a clathrin-mediated pathway that is dependent on membrane cholesterol and dynamin. This study provides new insight into the early host-virus interactions of SDDV and establishes a cellular platform for exploring host-directed intervention strategies against scale drop disease.