PROTECTIVE EFFICACY OF FORMALIN-INACTIVATED VACCINE AGAINST RED SEABREAM IRIDOVIRUS (RSIV) IN ASIAN SEABASS (LATES CALCARIFER)

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Date
2022
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KARNATAKA VETERINARY, ANIMAL AND FISHERIES SCIENCES UNIVERSITY, BIDAR
Abstract
Red seabream iridovirus (RSIV) was recently reported in India from cage cultures of Asian seabass causing high mortality and economic losses. Currently, no antiviral therapy or vaccines are available for the control of this pathogen. Hence, the present study was aimed to develop formalin inactivated vaccine to investigate the vaccine efficacy in Asian seabass. The virus used in the study was initially isolated from diseased Asian seabass and stored at -80oC. Confirmation of the RSIV was done by extracting the virus DNA from spleen and kidney tissues of infected fish. The results of the PCR assay showed a 568bp targeting DNA polymerase gene of the RSIV. Further, RSIV was propagated using cell lines under in-vitro conditions using the virus extracted from the spleen and kidney tissues of infected fish was inoculated onto SISK cell lines. Cytopathic effect (CPE) was observed in RSIV infected cells from 2nd post infection, which included rounding and enlargement of cells followed by cell death on the 7th day. The harvested virus stock was quantified by endpoint dilution assay and found to contain 106.3 TCID50/ml. Inactivation of the virus was performed using 0.1% of formalin for 10 days in 4°C and confirmed by negative CPE in SISK cells after 2-3 blind passages and then formalin inactivated virus (FIV) was stored in 4°C until use. Further, efficacy of FIV was carried out against RSIV in Asian seabass. Vaccinated fish did not exhibit typical clinical symptoms of RSIV infection and mortality is less, therefore the FIV was safer to use. After 21dpv fish were challenged with virulent RSIV-LC strain and after 14dpc relative percentage survival (RPS) was calculated. Asian seabass immunized with FIV showed high level of protection with RPS value of 86.6%. Therefore, further investigations for assess its efficacy against RSIV challenge in field trail and commercialization are require.
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