Recombinant lactobacillus expressing G protein of spring viremia of carp virus (SVCV) combined with ORF81 protein of koi herpesvirus (KHV): A promising way to induce protective immunity against SVCV and KHV infection in cyprinid fish via oral vaccination.

Spring viremia of carp virus (SVCV) and koi herpesvirus (KHV) are highly contagious and pathogenic to cyprinid fish, causing enormous economic losses in aquaculture. Although DNA vaccines reported in recent years could induce protective immune responses in carps against these viruses via injection, there are a number of consequences and uncertainties related to DNA vaccination. Therefore, more effective and practical method to induce protective immunity such as oral administration would be highly desirable. In this study, we investigated the utilities of a genetically engineered Lactobacillus plantarum (L. plantarum) coexpressing glycoprotein (G) of SVCV and ORF81 protein of KHV as oral vaccine to induce protective immunity in carps via oral vaccination. The surface-displayed recombinant plasmid pYG-G-ORF81 was electroporated into L. plantarum, giving rise to LP/pYG-G-ORF81, where expression and localization of G-ORF81 fusion protein from the LP/pYG-G-ORF81 was identified by SDS-PAGE, Western blotting and immunofluorescence assay. Bait feed particles containing the LP/pYG-G-ORF81 were used as vaccine to immunize carps via gastrointestinal route. Compared to control groups, the carps orally immunized with the LP/pYG-G-ORF81 were induced significant levels of immunoglobulin M (IgM), and its immunogenicity was confirmed by viral loads reduction detected by PCR assay after virus challenge followed by an effective protection rate 71% in vaccinated carps and 53% in vaccinated koi until at days 65 post challenge, respectively. Our study here demonstrates, for the first time, the ability of recombinant L. plantarum as oral vaccine against SVCV and KHV infection in carps, suggesting a practical multivalent strategy for the control of spring viremia of carp and koi herpesvirus disease.