Viral Erythrocytic Necrosis: Natural Occurrence in Pacific Salmon and Experimental Transmission

Abstract

A necrotic disease of erythrocytes of chum (Oncorhynchus keta) and pink (O. gorbuscha) salmon is described at the light and electron microscopic level. The disease is characterized by a single cytoplasmic inclusion in affected erythrocytes and by the presence of an associated intraerytnrocytic virus probably belonging to the icosahedral cytoplasmic deoxyribovirus (ICDV) group. Isolation of the virus was unsuccessful, but viral etiology was implicated by inoculation of chum and pink salmon using filtered preparations from diseased specimens of the former. Chinook (O. tshawytscha), coho (O. kisutch), andsockeye (O. nerka) salmon proved refractory. Key words: viral disease, Pacific salmon, blood, erythrocytes, anemia

DNA viruses associated with diseases of marine and anadromous fish

“…Structural details reported were an outer electron dense layer 8 nm wide, a less electron dense layer 16 nm wicle and a densely staining core approximately 100 nm in diameter which contained a 40 nm central electron translucent area. The ENV of herring then more closely resembles that described in salmonids (Evelyn & Traxler, 1978) and is distinct from that in cod or blenny .…”

“…Nuclear degeneration is also frequently observed, especially in Atlantic cod (Walker & Sherburne, 1977). Since there is redundancy in referring to PEN in specific fish, the infection is now more appropriately known as VEN, for viral erythrocytic necrosis (Evelyn & Traxler, 1978). The host range of VEN is broad and includes over 20 species of marine and anadromous fish.…”

“…In Pacific salmon, the disease has been diagnosed over a wide range of temperatures (6.5-19°C) but appears to be most severe during the summer (Evelyn & Traxler, 1978). With the exception of anemia in naturally and experimentally infected salmonids, no clinical signs of disease are apparent (Evelyn & Traxler, 1978).…”

“…With the exception of anemia in naturally and experimentally infected salmonids, no clinical signs of disease are apparent (Evelyn & Traxler, 1978). In this regard, Reno & Nicholson (1980) have demonstrated that erythrocytes from affected Atlantic cod were significantly more susceptible to lysis when maintained in vitro than were erythrocytes from uninfected cod.…”

“…Evelyn & Traxler (1978) reported mortalities up to 0.3 % per day in chum salmon that were attributable to VEN, however, the natural outbreaks were usually complicated by the presence of vibriosis and bacterial kidney disease. Rohovec & Amandi (1981) reported cytoplasmic inclusions in the erythrocytes of spawning coho and chinook salmon and steelhead trout in Oregon hatcheries.…”