Development, distribution and expression of a DNA vaccine against nodavirus in Asian Seabass,Lates calcarifier(Bloch, 1790)

Abstract

Fish nodavirus (betanodavirus), a viral pathogen responsible for viral nervous necrosis (VNN) was isolated from infected Asian sea bass (Lates calcarifer). The distribution, clearance and expression of nodavirus vaccine, on the basis of DNA vaccine (pFNCPE42 DNA-pcDNA3.1) construction, were analysed in tissues of the Asian seabass by PCR, RT-PCR, ELISA and Immunohistochemistry. Fish immunized with a single intramuscular injection of 20 μg of the pFNCPE42-DNA vaccine showed a significant increase in the serum antibody level in the 3rd week after vaccination, compared to control eukaryotic expression vector pcDNA3.1 vaccinated fish. Results from PCR studies indicated that the vaccine-containing plasmids were distributed in heart, intestine, gill, muscle and liver 10 days after vaccination. Clearance of pFNCPE42-DNA vaccine was studied at 10, 25, 50, 75 and 100 days of post vaccination (d p.v). At 100 days p.v. pFNCPE42-DNA was cleared from muscle of vaccinated sea bass. In vitro and in vivo expression of fish nodavirus capsid protein gene (FNCP) was determined by fluorescent microscopy. Asian seabass was immunized with pFNCPE42-DNA vaccine at a dose of 20 μg per fish and were challenged with betanodavirus by intramuscular injection. The vaccinated seabass was protected from nodaviral infection and 77.33% of relative percent survival (RPS) was recorded.