Abstract
Iridoviral disease is one of the newly emerging major diseases in aquaculture industry cable of killing over 90% hatchery-grow out population. Here we briefly review and describe our recent studies on ultrastructure, morphogenesis and antigenesis of a grouper iridovirus isolate. A pathogenic iridovirus was isolated from diseased grouper, Epinephelus malabaricus in Singapore. The virus has been characterized as a novel species of ranavirus. Ultrastructure and morphogenesis of the virus was investigated by electron microscopy. Abundant cytoplasmic icosahedral virions presented in the virusinfected grouper cells (GP cell line). The intracellular nucleocapsid was 154 nm between opposite sides, and 176 nm between opposite vertices with an inner electron dense core of 93 nm. The purified virus particles were enveloped with a size about 200 nm. After digested with protease K or degraded with detergents, the viral envelope was removed leaving inner two layers of membrane and regular array of capsid units with a size of 5 nm was visible. Different stages of the virus entry, amplification, assembly, maturation and release were observed in cytoplasm of virus-infected cells. The viral antigens were analyzed and characterized using rabbit IgG against the grouper iridovirus. More than 10 antigenic proteins were distinguished by Western Blot. Immune electron microscopy revealed that the antigens were mainly located at the viral envelope.
