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Viral fitness does not correlate with three genotype displacement events involving infectious hematopoietic necrosis virus.

ABSTRACT: Viral genotype displacement events are characterized by the replacement of a previously dominant virus genotype by a novel genotype of the same virus species in a given geographic region. We examine here the fitness of three pairs of infectious hematopoietic necrosis virus (IHNV) genotypes involved in three major genotype displacement events in Washington state over the last 30 years to determine whether increased virus fitness correlates with displacement. Fitness was assessed using in vivo assays to measure viral replication in single infection, simultaneous co-infection, and sequential superinfection in the natural host, steelhead trout. In addition, virion stability of each genotype was measured in freshwater and seawater environments at various temperatures. By these methods, we found no correlation between increased viral fitness and displacement in the field. These results suggest that other pressures likely exist in the field with important consequences for IHNV evolution.

SUBMITTER: Kell AM

PROVIDER: S-EPMC4157104 | biostudies-literature | 2014 Sep

REPOSITORIES: biostudies-literature

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Viral fitness does not correlate with three genotype displacement events involving infectious hematopoietic necrosis virus.

Kell Alison M AM Wargo Andrew R AR Kurath Gael G

Virology 20140726

Viral genotype displacement events are characterized by the replacement of a previously dominant virus genotype by a novel genotype of the same virus species in a given geographic region. We examine here the fitness of three pairs of infectious hematopoietic necrosis virus (IHNV) genotypes involved in three major genotype displacement events in Washington state over the last 30 years to determine whether increased virus fitness correlates with displacement. Fitness was assessed using in vivo ass ...[more]

PMID: 25068402

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Project description:Many pathogens interact and evolve in communities where more than one host species is present, yet our understanding of host-pathogen specialization is mostly informed by laboratory studies with single species. Managing diseases in the wild, however, requires understanding how host-pathogen specialization affects hosts in diverse communities. Juvenile salmonid mortality in hatcheries caused by infectious hematopoietic necrosis virus (IHNV) has important implications for salmonid conservation programs. Here, we evaluate evidence for IHNV specialization on three salmonid hosts and assess how this influences intra- and interspecific transmission in hatchery-reared salmonids. We expect that while more generalist viral lineages should pose an equal risk of infection across host types, viral specialization will increase intraspecific transmission. We used Bayesian models and data from 24 hatcheries in the Columbia River Basin to reconstruct the exposure history of hatcheries with two IHNV lineages, MD and UC, allowing us to estimate the probability of juvenile infection with these lineages in three salmonid host types. Our results show that lineage MD is specialized on steelhead trout and perhaps rainbow trout (both Oncorhynchus mykiss), whereas lineage UC displayed a generalist phenotype across steelhead trout, rainbow trout, and Chinook salmon. Furthermore, our results suggest the presence of specialist-generalist trade-offs because, while lineage UC had moderate probabilities of infection across host types, lineage MD had a small probability of infection in its nonadapted host type, Chinook salmon. Thus, in addition to quantifying probabilities of infection of socially and economically important salmonid hosts with different IHNV lineages, our results provide insights into the trade-offs that viral lineages incur in multihost communities. Our results suggest that knowledge of the specialist/generalist strategies of circulating viral lineages could be useful in salmonid conservation programs to control disease.

Project description:The genome of infectious hematopoietic necrosis virus (IHNV), a salmonid novirhabdovirus, has been engineered to modify the gene order and to evaluate the impact on a possible attenuation of the virus in vitro and in vivo By reverse genetics, eight recombinant IHNVs (rIHNVs), termed NxGy according to the respective positions of the nucleoprotein (N) and glycoprotein (G) genes along the genome, have been recovered. All rIHNVs have been fully characterized in vitro for their cytopathic effects, kinetics of replication, and profiles of viral gene transcription. These rIHNVs are stable through up to 10 passages in cell culture. Following bath immersion administration of the various rIHNVs to juvenile trout, some of the rIHNVs were clearly attenuated (N2G3, N2G4, N3G4, and N4G1). The position of the N gene seems to be one of the most critical features correlated to the level of viral attenuation. The induced immune response potential in fish was evaluated by enzyme-linked immunosorbent spot assay (ELISPOT) and seroneutralization assays. The recombinant virus N2G3 induced a strong antibody response in immunized fish and conferred 86% of protection against wild-type IHNV challenge in trout, thus representing a promising starting point for the development of a live attenuated vaccine candidate.In Europe, no vaccines are available against infectious hematopoietic necrosis virus (IHNV), one of the major economic threats in fish aquaculture. Live attenuated vaccines are conditioned by a sensible balance between attenuation and pathogenicity. Moreover, nonsegmented negative-strain RNA viruses (NNSV) are subject to a transcription gradient dictated by the order of the genes in their genomes. With the perspective of developing a vaccine against IHNV, we engineered various recombinant IHNVs with reordered genomes in order to artificially attenuate the virus. Our results validate the gene rearrangement approach as a potent and stable attenuation strategy for fish novirhabdovirus and open a new perspective for design of vaccines against other NNSV.

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Viral fitness does not correlate with three genotype displacement events involving infectious hematopoietic necrosis virus.

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Viral fitness does not correlate with three genotype displacement events involving infectious hematopoietic necrosis virus.

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