epizootic haematopoietic necrosis virus

International Common Names

• English: epizootic hematopoietic necrosis virus

English acronym

• EHNV

• Domain: Virus
•     Group: "ssDNA viruses"
•         Group: "DNA viruses"
•             Family: Iridoviridae
•                 Genus: Ranavirus
•                     Species: epizootic haematopoietic necrosis virus

Fish ranaviruses are distinct agents, although they have similar hexagonal morphology and size (slightly over 130-140 nm), number and weight of structural polypeptides and common antigens (Hedrick et al., 1992). They replicate in cytoplasm and induce inclusion bodies as centres of virus production. The cytopathic effect in cell cultures is characterized by focal rounding up of cells from substrate and cell lysis, expansion of these changes and destruction of the cell monolayer. According to Essani and Granoff (1989), the pattern and number of polypeptides in ranaviruses differ from those in lymphocystis virus and in two goldfish iridoviruses isolated by Berry et al. (1983). The PCR with primer sets for EHNV amplified a genomic DNA segment from IOTF (Hedrick and McDowell, 1995).

Iridoviruses are presumably internalized by the cell during a receptormediated endocytosis. Budding and envelopment at the plasma membrane secure the exit of mature IW (Granzow et al., 1997).

Epizootic haemopoietic necrosis virus replicates in BB, BF-2, FHM, RTG-2 and several other cells. Langdon and Humphrey (1987) and Langdon et al. (1988) obtained highest virus yields in FHM cells. Bluegill fry cells kept at 20-22°C are recommended in the OIE Manual (1995b) for the isolation of EHNV. Sheatfish iridovirus is readily isolated in BF-2 and FHM cells at 20-30°C. Black bullhead iridovirus grows in EPC, CCO and BF-2 cells, with optimum plaque development in the latter. Iridovirus of ornamental tropical fish replicates in the same cell lines. Largemouth bass virus was isolated in FHM cells. Perch and trout isolates of EHNV differ in the molecular weights of some structural proteins (Hengstberger et al., 1993).

The range of cells susceptible to Bohle iridovirus and EHNV is very similar. The two viruses exhibit a high degree of cross-reactivity in ELISA tests, have very similar morphology and structure but differ in size, cytopathic effect on host cells, molecular weights of proteins, polypeptide profiles, Western blots and site of virus release from cells (Speare and Smith, 1992; Hengstberger et al., 1993).

The persistence of EHNV in water and cell-culture medium at optimum temperature for EHN outbreaks in redfin perch is important in epizootiology.