Inactivation of nervous necrosis virus infecting grouper (Epinephelus coioides) by epinecidin-1 and hepcidin 1–5 antimicrobial peptides, and downregulation of Mx2 and Mx3 gene expressions

Betanodaviruses are one of the serious pathogens in nervous necrosis viral (NNV) disease that brings about mortality in the larval stage of grouper (Epinephelus coioides). In this study, the efficacy of pretreatment, co-treatment, and posttreatment with the antimicrobial epinecidin-1 and hepcidin 1–5 peptides against a betanodavirus was evaluated by intraperitoneal inoculation in grouper. The results showed that co-treatment of epinecidin-1 or hepcidin 1–5 with the virus was effective in promoting a significant decrease in grouper mortality. Re-challenge with virus again after 30 day in co-treated grouper groups showed high survival suggesting that epinecidin-1 and hepcidin 1–5 enhanced fish survival. However, grouper inoculated with NNV and then inoculated with epinecidin-1 8 h later showed significantly different survival from the group inoculated with virus alone, suggesting that epinecidin-1 can be used as a drug to rescue infected grouper. Infection after pretreatment, co-treatment, and posttreatment with epinecidin-1 or hepcidin 1–5 was verified by RT-PCR which showed downregulation of Mx2 and Mx3 gene expressions. All these data strongly suggest that epinecidin-1 and hepcidin 1–5 are effective peptides for protecting grouper larvae by reducing NNV infection.