A major capsid protein subunit vaccine can block vertical transmission of LMBV in largemouth bass broodstock.

Largemouth bass virus (LMBV) is the most prevalent and threatening virus in largemouth bass aquaculture. To establish effective control measures of LMBV, this study vaccinated broodstock with an LMBV MCP subunit vaccine to assess whether the subunit vaccine could activate maternal immunity to block vertical transmission of LMBV. Fourteen days post-immunization, significant upregulation of IgM, IgT, IL-6, TNF-α, and CD4 gene expression was observed in the relevant tissues of broodstocks. Serum titers reached their peak at 21 days post-immunization as detected by ELISA within 28 days. After challenge, the subunit vaccine achieved a relative protection rate of 87.4%. The MCP + LMBV group showed a significant reduction in viral load in the relevant tissues and a marked alleviation of histopathological damage compared to the Control + LMBV group. Compared to the Control group, vaccinated broodstocks exhibited normal spawning behavior, with no significant differences in spawning trends or total egg production, while egg production in the Control + LMBV group was significantly reduced. The fertilization and hatching rates in the MCP + LMBV group were 94.06% and 94.50%, respectively, with the hatching rate 27.77% higher than the Control + LMBV group. In the MCP + LMBV group, the virus positivity rate for both gonads and fertilized eggs were 0.0%. This study confirms that LMBV can be transmitted vertically from infected broodstock to their offspring, however, the MCP subunit vaccine can activate maternal immunity to block vertical transmission of LMBV, which provides a new approach to protect largemouth bass offspring from LMBV infection.