title: Differential growth of U and M type infectious haematopoietic necrosis virus in a rainbow trout-derived cell line, RTG-2.
abstract: Infectious haematopoietic necrosis virus (IHNV) is one of the most important viral pathogens of salmonids. In rainbow trout, IHNV isolates in the M genogroup are highly pathogenic, while U genogroup isolates are significantly less pathogenic. We show here that, at a multiplicity of infection (MOI) of 1, a representative U type strain yielded 42-fold less infectious virus than an M type strain in the rainbow trout-derived RTG-2 cell line at 24 h post-infection (p.i.). However, at an MOI of 10, there was only fivefold difference in the yield of infectious virus between the U and M strains. Quantification of extracellular viral genomic RNA suggested that the number of virus particles released from cells infected with the U strain at a MOI of 1 was 47-fold lower than from M-infected cells, but U and M virions were equally infectious by particle to infectivity ratios. At an MOI of 1, U strain intracellular viral genome accumulation and transcription were 37- and 12-fold lower, respectively, than those of the M strain at 24 h p.i. Viral nucleocapsid (N) protein accumulation in U strain infections was fivefold lower than in M strain infections. These results suggest that the block in U type strain growth in RTG-2 cells was because of the effects of reduced genome replication and transcription. The reduced growth of the U strain does not seem to be caused by defective genes, because the U and M strains grew equally well in the permissive epithelioma papulosum cyprini cell line at an MOI of 1. This suggests that host-specific factors in RTG-2 cells control the growth of the IHNV U and M strains differently, leading to growth restriction of the U type virus during the RNA synthesis step.
authors.affiliation: US Geological Survey, Western Fisheries Research Center, Seattle, WA 98115, USA.
authors.forename: J W
authors.initials: JW
authors.lastname: Park
authors.forename: C H
authors.initials: CH
authors.lastname: Moon
authors.forename: A R
authors.initials: AR
authors.lastname: Wargo
authors.forename: M K
authors.initials: MK
authors.lastname: Purcell
authors.forename: G
authors.initials: G
authors.lastname: Kurath
mesh_terms: D000818:Animals; D002460:Cell Line; D005393:Fish Diseases / Q000821:virology*; D015967:Gene Expression Regulation, Viral; D016679:Genome, Viral / Q000235:genetics; D054884:Host-Pathogen Interactions; D029142:Infectious hematopoietic necrosis virus / Q000145:classification / Q000235:genetics / Q000254:growth & development* / Q000472:pathogenicity; D019590:Nucleocapsid Proteins / Q000378:metabolism; D017686:Oncorhynchus mykiss / Q000821:virology*; D018353:Rhabdoviridae Infections / Q000662:veterinary* / Q000821:virology; D013997:Time Factors; D014779:Virus Replication
chemical_list: D019590:Nucleocapsid Proteins