We investigated mass mortalities of koi, Cyprinus carpio Linnaeus, 1758, experienced in South Indian fish farms by virus isolation, electron microscopy, PCR detection, sequencing of capsid protein gene and transmission studies. Samples of moribund koi brought to the laboratory suffered continuous mortality exhibiting swimming abnormalities, intermittent surfacing and skin darkening. Irido-like virus was isolated from the infected fish in the indigenous snakehead kidney cell line (SNKD2a). Icosahedral virus particles of 100 to 120 nm were observed in the infected cell cultures, budding from the cell membrane. Virus transmission and pathogenicity studies revealed that horizontal transmission occurred associated with mortality. PCR analysis of infected fish and cell cultures confirmed the presence of Ranavirus capsid protein sequences. Sequence analysis of the major capsid protein gene showed an identity of 99.9% to that of largemouth bass virus isolated from North America. Detection and successful isolation of this viral agent becomes the first record of isolation of a virus resembling Santee-Cooper Ranavirus from a koi and from India. We propose the name koi ranavirus to this agent.
Background: Control of viral disease outbreaks in aquaculture and minimizing the loss of production can be achieved by development of effective vaccines. Efficacy of these vaccines can be improved by using adjuvants, immunostimulants or vaccine carriers. In this study, inactivated similar damselfish virus (SRDV) vaccine was prepared and expression profiles of immune related genes against virus challenge of the vaccine were investigated in seabass (Lates calcarifer). Methods: Formalin-inactivated virus vaccine was developed to assess its immune responses to SRDV challenge in fish. The immune response was induced by intra-peritoneal injection with inactivated viral vaccine added Quil-A® adjuvant. The transcriptional levels of immune genes IRF-7 and IL-10 were evaluated in the spleen and kidney of seabass from different groups by quantitative real-time RT-PCR assays. Result: Expression profiles of both genes (IRF-7 and IL-10) in the kidney and spleen of seabass immunized with vaccine added adjuvant were up-regulated at 48 hpi of the virus. In comparison, spleen of seabass immunized with vaccine added adjuvant showed highest expression profiles than kidney. The current study provides evidence for the presence of expression profiles of immune-related genes during the SRDV infection. The study also strongly suggests that Quil-A® adjuvant enhances the immune response of the vaccine candidates.
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