Characterization and immunological studies of reovirus in tropical fish

Abstract

An unidentified virus was isolated from moribund cultured threadfin (Eleutheronema tetradactylus) fingerlings, propagated, characterized and identified to be of the genus Aquareovirus, and was designated as threadfin reovirus (TFV). TFV was pathogenic to threadfin fingerlings (100% mortality) and also to sea bass fingerlings (62.5% mortality). Using RT-PCR, the inner (ICP) and outer (OCP) coat proteins of TFV were cloned, sequenced and analyzed. An RT-PCR assay was then developed for the detection of various Aquareovirus strains. The assay was able to specifically detect TFV and other aquareovirus isolates such as GPV, CSV, SBR and GCRV, and also able to detect aquareovirus in experimentally virus-infected fish showing clinical symptoms as well as in asymptomatic virus-carrier fish. The ICP and OCP viral proteins were then expressed in E. coli and a DNA vaccine was also constructed. Vaccination of the recombinant ICP and OCP proteins, and DNA vaccine to carp (Cyprinus carpio), generated specific TFV neutralizing antibodies. High neutralizing antibody titers were achieved when both the inner (ICP) and outer (OCP) coat proteins were administered during immunization, thus indicating that both the inner and outer coat proteins are essential for the development of immunity against TFV infection and maybe suitable candidate vaccines.