Abstract
Negatively stained EVA and EVEX with typical rhabdovirus shapes were measured using catalase crystals as the standard. Their mean sizes were 143.2×83.5 and 144.6×83.7 nm respec tively. The CPE caused by EVA and EVEX in RTG-2 cells were very similar, but they were clearly distinguishable from that of IHNV. They induced marginal hyperchromatosis, deforma of nuclei and formation of basophilic inclusions of irregular shapes in the cytoplasm of in fected cells. Finally, infected cells became round and then collapsed in pieces. By SEM observa of CPE caused by both viruses, it was found that infected cells having long filopodia became round with some shrinking. Serologically, there is close similarity between EVA and EVEX, but both are clearly different from IHNV and probably different from VHSV type II and 23-75 strain. Infectivity trials with rainbow trout fry were carried out at 10°C, 15°C and 20°C. Both EVA EVEX showed more severe pathogenicity at higher temperatures. Symptoms and histo pathological changes of fish infected with EVA and EVEX were similar to those of IHN, and included hemorrhage of skeletal muscles, intensive necrosis and hemorrhage of hematopoietictissue of the kidneys and focal necrosis of liver, spleen and panceras. The fact that EVEX showed strong pathogenicity even at 15°C makes us concerned about the introduction of a new viral disease in rainbow trout cultured in Japan.
