Effective protection against Ranavirus-type grouper iridovirus and Vibrio harveyi by priming a bivalent GrouperVAC-Irido-R-Vh followed by boosting a monovalent V. harveyi vaccine

Natural outbreaks of Ranavirus-type grouper iridovirus (GIV-R) and/or Vibrio harveyi result in massive mortalities and severe economic losses in grouper industry. However, effective vaccines against both pathogens have not yet been applied commercially. In this study, a water-in-oil formation of formalin-killed bivalent vaccine (Group-erVAC-Irido-R-Vh) against both GIV-R and V. harveyi and a monovalent vaccine (GrouperVAC-Vh) against V. harveyi were developed and evaluated both under laboratory and field trial tests. The result showed that the single intraperitoneally-injected grouper juveniles (N = 35) with bivalent GrouperVAC-Irido-R-Vh under labo-ratory condition were protected against GIV-R and V. harveyi at 21 days post vaccination (dpv) with relative percent survivals (RPS) of > 90% and 80%, respectively. In a field trial test (N = 7500), the effective protections of single intraperitoneally-injected fish were also observed in vaccinated grouper juveniles at 90 dpv, with RPSs of 87.5% and 70.4% against GIV-R and V. harveyi challenge, respectively, indicating that the bivalent GrouperVAC-Irido-R-Vh conferred effective protections against both GIV-R and V. harveyi infection for at least 3 months. Moreover, based on primary injection of GrouperVAC-Irido-R-Vh, a booster immunization of the single component of GrouperVAC-Vh (N = 4500) can prolong conferring effective protection against vibriosis caused by V. harveyi from 3 months to 9 months with an RPS of 88.2%. Given that the large-sized grouper is much less sensitive to GIV-R but remains highly susceptible to V. harveyi, we propose that the optimal immunization programs against GIV-R and V. harveyi are primary immunization with the bivalent GrouperVAC-Irido-R-Vh vaccine followed by boosting a monovalent GrouperVAC-Vh vaccine.

Automated summary

In this study, vaccines against Ranavirus-type grouper iridovirus (GIV-R) and/or Vibrio harveyi were developed and evaluated. The results showed that these vaccines provided effective protection against both pathogens. Additionally, booster immunization prolonged the duration of protection against V. harveyi infection.