ISOLATION AND CHARACTERIZATION OF A PATHOGENIC IRIDOVIRUS FROM CULTURED GROUPER (EPINEPHELUS SP.) IN TAIWAN

A new epizootic viral disease has threatened cultured grouper (Epineph elus sp.) in Taiwan since 1995. Icosahedral viral particles with a dia meter of 230 +/- 10 nm were observed in the spleen of moribund fish. C ell rounding, a cytopathic effect (CPE), was induced in KRE cell line by the virus isolated from diseased groupers. Virus infectivities decl ined rapidly during serial passages in the KRE cell line. The suscepti bility of the virus to chloroform and ether treatments indicates that the virus may be enveloped. When stained with acridine orange, the inc lusions in the KRE cells exhibited a greenish fluorescence, and this t ogether with the results of IUDR treatment suggest that the viral geno me of the virus is double-stranded DNA. Based on its general propertie s and viral morphology, the name Grouper Iridovirus of Taiwan (TGIV) w as proposed. When healthy juvenile groupers were experimentally infect ed by intraperitoneal injection with TGIV, cumulative mortalities reac hed 100% within 11 days, while no grouper died in the control groups. Virus similar in morphology to that observed in spontaneously diseased fish was then re-isolated from the experimentally infected groupers. These results suggest that this virus may be the causative agent of th e epizootic disease that now afflicts cultured grouper in Taiwan.