1
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Cano I, Santos EM, Moore K, Farbos A, van Aerle R. Evidence of Transcriptional Shutoff by Pathogenic Viral Haemorrhagic Septicaemia Virus in Rainbow Trout. Viruses 2021; 13:v13061129. [PMID: 34208332 PMCID: PMC8231187 DOI: 10.3390/v13061129] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2021] [Revised: 06/03/2021] [Accepted: 06/07/2021] [Indexed: 12/13/2022] Open
Abstract
The basis of pathogenicity of viral haemorrhagic septicaemia virus (VHSV) was analysed in the transcriptome of a rainbow trout cell line inoculated with pathogenic and non-pathogenic VHSV isolates. Although both VHSV isolates showed similar viral replication patterns, the number of differentially expressed genes was 42-fold higher in cells inoculated with the non-pathogenic VHSV at 3 h post inoculation (hpi). Infection with the non-pathogenic isolate resulted in Gene Ontologies (GO) enrichment of terms such as immune response, cytokine-mediated signalling pathway, regulation of translational initiation, unfolded protein binding, and protein folding, and induced an over-representation of the p53, PPAR, and TGF-β signalling pathways. Inoculation with the pathogenic isolate resulted in the GO enrichment of terms related to lipid metabolism and the salmonella infection KEGG pathway involved in the rearrangement of the cytoskeleton. Antiviral response was evident at 12hpi in cells infected with the pathogenic isolate. Overall, the data showed a delay in the response of genes involved in immune responses and viral sensing in cells inoculated with the pathogenic isolate and suggest transcriptional shutoff and immune avoidance as a critical mechanism of pathogenicity in VHSV. These pathways offer opportunities to further understand and manage VHSV pathogenicity in rainbow trout.
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Affiliation(s)
- Irene Cano
- International Centre of Excellence for Aquatic Animal Health, Cefas Weymouth Laboratory, Barrack Road, The Nothe, Weymouth DT4 8UB, Dorset, UK;
- Correspondence:
| | - Eduarda M. Santos
- Biosciences, College of Life and Environmental Sciences, University of Exeter, Stocker Road, Exeter EX4 4QD, Devon, UK;
- Sustainable Aquaculture Futures, Biosciences, College of Life and Environmental Sciences, University of Exeter, Stocker Road, Exeter EX4 4QD, Devon, UK
| | - Karen Moore
- Exeter Sequencing Service, Geoffrey Pope Building, University of Exeter, Exeter EX4 4QD, Devon, UK; (K.M.); (A.F.)
| | - Audrey Farbos
- Exeter Sequencing Service, Geoffrey Pope Building, University of Exeter, Exeter EX4 4QD, Devon, UK; (K.M.); (A.F.)
| | - Ronny van Aerle
- International Centre of Excellence for Aquatic Animal Health, Cefas Weymouth Laboratory, Barrack Road, The Nothe, Weymouth DT4 8UB, Dorset, UK;
- Sustainable Aquaculture Futures, Biosciences, College of Life and Environmental Sciences, University of Exeter, Stocker Road, Exeter EX4 4QD, Devon, UK
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2
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Wargo AR, Kurath G, Scott RJ, Kerr B. Virus shedding kinetics and unconventional virulence tradeoffs. PLoS Pathog 2021; 17:e1009528. [PMID: 33970967 PMCID: PMC8109835 DOI: 10.1371/journal.ppat.1009528] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2020] [Accepted: 04/03/2021] [Indexed: 11/19/2022] Open
Abstract
Tradeoff theory, which postulates that virulence provides both transmission costs and benefits for pathogens, has become widely adopted by the scientific community. Although theoretical literature exploring virulence-tradeoffs is vast, empirical studies validating various assumptions still remain sparse. In particular, truncation of transmission duration as a cost of virulence has been difficult to quantify with robust controlled in vivo studies. We sought to fill this knowledge gap by investigating how transmission rate and duration were associated with virulence for infectious hematopoietic necrosis virus (IHNV) in rainbow trout (Oncorhynchus mykiss). Using host mortality to quantify virulence and viral shedding to quantify transmission, we found that IHNV did not conform to classical tradeoff theory. More virulent genotypes of the virus were found to have longer transmission durations due to lower recovery rates of infected hosts, but the relationship was not saturating as assumed by tradeoff theory. Furthermore, the impact of host mortality on limiting transmission duration was minimal and greatly outweighed by recovery. Transmission rate differences between high and low virulence genotypes were also small and inconsistent. Ultimately, more virulent genotypes were found to have the overall fitness advantage, and there was no apparent constraint on the evolution of increased virulence for IHNV. However, using a mathematical model parameterized with experimental data, it was found that host culling resurrected the virulence tradeoff and provided low virulence genotypes with the advantage. Human-induced or natural culling, as well as host population fragmentation, may be some of the mechanisms by which virulence diversity is maintained in nature. This work highlights the importance of considering non-classical virulence tradeoffs.
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Affiliation(s)
- Andrew R. Wargo
- Virginia Institute of Marine Science, William & Mary, Gloucester Point, Virginia, United States of America
| | - Gael Kurath
- U.S. Geological Survey, Western Fisheries Research Center, Seattle, Washington, United States of America
| | - Robert J. Scott
- Department of Biology, University of Washington, Seattle, Washington, United States of America
| | - Benjamin Kerr
- Department of Biology, University of Washington, Seattle, Washington, United States of America
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3
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Louboutin L, Cabon J, Vigouroux E, Morin T, Danion M. Comparative analysis of the course of infection and the immune response in rainbow trout (Oncorhynchus mykiss) infected with the 5 genotypes of infectious hematopoietic necrosis virus. Virology 2021; 552:20-31. [DOI: 10.1016/j.virol.2020.09.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2020] [Revised: 09/03/2020] [Accepted: 09/03/2020] [Indexed: 12/29/2022]
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4
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Jones DR, Rutan BJ, Wargo AR. Impact of Vaccination and Pathogen Exposure Dosage on Shedding Kinetics of Infectious Hematopoietic Necrosis Virus (IHNV) in Rainbow Trout. JOURNAL OF AQUATIC ANIMAL HEALTH 2020; 32:95-108. [PMID: 32443164 PMCID: PMC7540492 DOI: 10.1002/aah.10108] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/08/2019] [Revised: 04/03/2020] [Accepted: 04/27/2020] [Indexed: 06/11/2023]
Abstract
Vaccine efficacy in preventing clinical disease has been well characterized. However, vaccine impacts on transmission under diverse field conditions, such as variable pathogen exposure dosages, are not fully understood. We evaluated the impacts of vaccination on disease-induced host mortality and shedding of infectious hematopoietic necrosis virus (IHNV) in Rainbow Trout Oncorhynchus mykiss. Fish, in up to three different genetic lines, were exposed to different dosages of IHNV to simulate field variability. Mortality and viral shedding of each individual fish were quantified over the course of infection. As the exposure dosage increased, mortality, number of fish shedding virus, daily virus quantity shed, and total amount of virus shed also increased. Vaccination significantly reduced mortality but had a much smaller impact on shedding, such that vaccinated fish still shed significant amounts of virus, particularly at higher viral exposure dosages. These studies demonstrate that the consideration of pathogen exposure dosage and transmission are critical for robust inference of vaccine efficacy.
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Affiliation(s)
- Darbi R. Jones
- Virginia Institute of Marine ScienceWilliam & MaryPost Office Box 1346, 1370 Greate RoadGloucester PointVirginia23062USA
| | - Barbara J. Rutan
- Virginia Institute of Marine ScienceWilliam & MaryPost Office Box 1346, 1370 Greate RoadGloucester PointVirginia23062USA
| | - Andrew R. Wargo
- Virginia Institute of Marine ScienceWilliam & MaryPost Office Box 1346, 1370 Greate RoadGloucester PointVirginia23062USA
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5
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Cabon J, Almeras F, Baud M, Pallandre L, Morin T, Louboutin L. Susceptibility of pike Esox lucius to VHSV and IHNV and potential transmission to rainbow trout Oncorhynchus mykiss. DISEASES OF AQUATIC ORGANISMS 2020; 139:175-187. [PMID: 32495744 DOI: 10.3354/dao03474] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Determining the origin of recurrent outbreaks of fish diseases occurring on fish farms is essential for disease prevention and control measures. In this study, we investigated the potential reservoir role of wild fish species living near salmonid farms which were regularly found to be positive for viral hemorrhagic septicemia virus (VHSV). In addition to VHSV, infectious hematopoietic necrosis virus (IHNV) was also isolated from several pike Esox lucius samples collected from a pond near the salmonid farms of interest. All isolates of VHSV and IHNV analyzed had 100% identical partial glycoprotein gene sequences. VHSV pike strain OO128-25 belonged to the Ia genotype and shared 99.1 to 99.5% nucleotide identity with strains recently isolated from the farms. IHNV pike strain OO121-8, European genotype, appeared to be different from strains from France characterized since the first isolation in 1987. Isolates representative of both viral species were highly virulent in rainbow trout Oncorhynchus mykiss. OO128-25 induced 65% mortality in pike fingerlings, whereas only weak mortality was observed with OO121-8, despite characteristic symptoms in infected fish. High levels of specific antibodies to VHSV and IHNV were detected in adult pike in the absence of clinical signs. Infection of rainbow trout in contact with experimentally VHSV- or IHNV-infected pike fingerlings indicates possible horizontal transmission. These results suggest that pike could act as a reservoir for VHSV and IHNV in the wild, providing additional evidence to explain viral persistence and resurgence in certain areas.
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Affiliation(s)
- J Cabon
- French Agency for Food, Environmental and Occupational Health and Safety, Ploufragan-Plouzané-Niort Laboratory, Viral Fish Diseases Unit, National Reference Laboratory for Regulated Fish Diseases, 29280 Plouzané, France
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6
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Tapia D, Barría A, Kuznar J, Yáñez JM. Comparison of mortality and viral load in rainbow trout (Oncorhynchus mykiss) infected with infectious pancreatic necrosis virus (IPNV) genogroups 1 and 5. JOURNAL OF FISH DISEASES 2020; 43:139-146. [PMID: 31724200 DOI: 10.1111/jfd.13113] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/18/2019] [Revised: 10/14/2019] [Accepted: 10/16/2019] [Indexed: 06/10/2023]
Abstract
Infectious pancreatic necrosis virus (IPNV) is the aetiological agent of a highly contagious disease that affects farmed salmonids. IPNV isolates have been phylogenetically classified into eight genogroups, of which two are present in Chile, genogroups 1 and 5. Here, we compare the mortality rate caused by isolates from both genogroups in rainbow trout (Oncorhynchus mykiss) fry to determine if there is an association between host susceptibility and phylogenetic characterization of IPNV. Fish were challenged by immersion with one of four isolates (two for each genogroup), and mortality curves were assessed after 30 days. Viral load was measured in all mortalities and in live fish sampled at 1, 7 and 20 days post-infection. Although mortality was low throughout the challenge, differences were found between fish infected with different isolates. Both isolates from genogroup 1 caused greater cumulative mortalities than either of the isolates from genogroup 5. When combined, the overall mortality rate of fish challenged with genogroup 1 isolates was significantly higher than those infected with genogroup 5. However, viral load was lower on trout infected with genogroup 1 isolates. These results suggest that rainbow trout are more susceptible to IPNV isolates from genogroup 1 than genogroup 5.
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Affiliation(s)
- David Tapia
- Doctorado en Acuicultura, Programa Cooperativo Universidad de Chile, Universidad Católica del Norte, Pontificia Universidad Católica de Valparaíso, Santiago, Chile
| | - Agustín Barría
- Facultad de Ciencias Veterinarias y Pecuarias, Universidad de Chile, Santiago, Chile
| | - Juan Kuznar
- Centro de Investigación y Gestión de Recursos Naturales, Instituto de Química y Bioquímica, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
| | - José M Yáñez
- Facultad de Ciencias Veterinarias y Pecuarias, Universidad de Chile, Santiago, Chile
- Núcleo Milenio INVASAL, Concepción, Chile
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7
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Jalali SAH, Mohammadinezhad R, Mohammadi A, Latifian MH, Talebi M, Soleimanin-Zad S, Golkar P, Hemmatzadeh F. Molecular evolution and selection pressure analysis of infectious hematopoietic necrosis virus (IHNV) revealed the origin and phylogenetic relationship of Iranian isolates in recent epidemics in Iran. Virology 2019; 535:45-58. [PMID: 31272011 DOI: 10.1016/j.virol.2019.06.012] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2019] [Revised: 06/19/2019] [Accepted: 06/19/2019] [Indexed: 12/15/2022]
Abstract
Infectious hematopoietic necrosis virus (IHNV) is the causative agent for a lethal salmonid disease. In this study, we surveyed the IHNV's epidemiology, diversity and the origin of infection in Iran. Phylogenetic analysis revealed that Iranian isolates belonged to one of the two lineages of E genogroup. Subsequently, a combination of phylogenetic, antigenic and structural analysis was performed to investigate the evolution of E genogroup lineages. Site-specific analysis of the viral glycoprotein showed different co-evolving and positively selected sites in each lineage. Most of these sites were mapped to the predicted antigenic patches of the glycoprotein. Further characterization revealed E lineages can be differentiated, in part, by specific mutations at positions 91 and 130, which are located in the structurally flexible regions of the glycoprotein, suggesting a key adaptative role for these sites. These data may assist in better monitoring the emerging isolates in regions infected to IHNV from E genogroup.
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Affiliation(s)
- Seyed Amir Hossein Jalali
- Research Institute for Biotechnology and Bioengineering, Isfahan University of Technology, Isfahan, 84156-83111, Iran; Department of Natural Resources, Isfahan University of Technology, Isfahan, 84156-83111, Iran.
| | - Rezvan Mohammadinezhad
- Research Institute for Biotechnology and Bioengineering, Isfahan University of Technology, Isfahan, 84156-83111, Iran
| | - Ashraf Mohammadi
- Human Viral vaccine Department, Razi Vaccine and Serum Research Institute (RVSRI), Hessark Karadj Agricultural Research, Education and Extension Organization (AREEO), Tehran, Iran
| | - Mohamad Hassan Latifian
- Department of Agricultural Biotechnology, College of Agriculture, Isfahan University of Technology, Isfahan, 8415683111, Iran
| | - Majid Talebi
- Research Institute for Biotechnology and Bioengineering, Isfahan University of Technology, Isfahan, 84156-83111, Iran; Department of Agricultural Biotechnology, College of Agriculture, Isfahan University of Technology, Isfahan, 8415683111, Iran
| | - Sabihe Soleimanin-Zad
- Research Institute for Biotechnology and Bioengineering, Isfahan University of Technology, Isfahan, 84156-83111, Iran; Department of Food Science and Technology, College of Agriculture, Isfahan University of Technology, Isfahan, Iran
| | - Pouran Golkar
- Research Institute for Biotechnology and Bioengineering, Isfahan University of Technology, Isfahan, 84156-83111, Iran
| | - Farhid Hemmatzadeh
- School of Animal and Veterinary Sciences, The University of Adelaide, Roseworthy, SA, Australia
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8
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Doumayrou J, Ryan MG, Wargo AR. Method for serial passage of infectious hematopoietic necrosis virus (IHNV) in rainbow trout. DISEASES OF AQUATIC ORGANISMS 2019; 134:223-236. [PMID: 31169128 DOI: 10.3354/dao03368] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Transmission is a fundamental component of pathogen fitness. A better understanding of pathogen transmission can greatly improve disease management. In particular, controlled studies of multiple rounds of natural transmission (i.e. serial passage) can provide powerful epidemiological and evolutionary inferences. However, such studies are possible in only a few systems because of the challenges in successfully initiating and maintaining transmission in the laboratory. Here we developed an efficient and reproducible cohabitation method for conducting controlled experiments investigating the effects of serial passage on infectious hematopoietic necrosis virus (IHNV) in rainbow trout. This method was used to investigate the transmission efficiency and kinetics of viral shedding of IHNV over 3 serial passages. Transmission efficiency decreased from 100 to 62.5% over the passage steps and was associated with a decrease in virus shedding into water. A shift in the peak of viral shedding was also observed, from Day 2 post immersion for passage 0 to at least 24 h later for all subsequent passages. Finally, the characterization of viruses after 1 round of transmission and propagation on cells showed no change in glycoprotein (G gene) sequences or viral virulence compared to the ancestral virus stock. The methods developed provide valuable tools for reproducible population-level studies of IHNV epidemiology and evolution.
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Affiliation(s)
- Juliette Doumayrou
- Virginia Institute of Marine Science, William & Mary, PO Box 1346, Gloucester Point, VA 23062, USA
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9
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Breyta R, Brito I, Ferguson P, Kurath G, Naish KA, Purcell MK, Wargo AR, LaDeau S. Transmission routes maintaining a viral pathogen of steelhead trout within a complex multi-host assemblage. Ecol Evol 2017; 7:8187-8200. [PMID: 29075442 PMCID: PMC5648648 DOI: 10.1002/ece3.3276] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2017] [Revised: 05/22/2017] [Accepted: 06/28/2017] [Indexed: 01/06/2023] Open
Abstract
This is the first comprehensive region wide, spatially explicit epidemiologic analysis of surveillance data of the aquatic viral pathogen infectious hematopoietic necrosis virus (IHNV) infecting native salmonid fish. The pathogen has been documented in the freshwater ecosystem of the Pacific Northwest of North America since the 1950s, and the current report describes the disease ecology of IHNV during 2000-2012. Prevalence of IHNV infection in monitored salmonid host cohorts ranged from 8% to 30%, with the highest levels observed in juvenile steelhead trout. The spatial distribution of all IHNV-infected cohorts was concentrated in two sub-regions of the study area, where historic burden of the viral disease has been high. During the study period, prevalence levels fluctuated with a temporal peak in 2002. Virologic and genetic surveillance data were analyzed for evidence of three separate but not mutually exclusive transmission routes hypothesized to be maintaining IHNV in the freshwater ecosystem. Transmission between year classes of juvenile fish at individual sites (route 1) was supported at varying levels of certainty in 10%-55% of candidate cases, transmission between neighboring juvenile cohorts (route 2) was supported in 31%-78% of candidate cases, and transmission from adult fish returning to the same site as an infected juvenile cohort was supported in 26%-74% of candidate cases. The results of this study indicate that multiple specific transmission routes are acting to maintain IHNV in juvenile fish, providing concrete evidence that can be used to improve resource management. Furthermore, these results demonstrate that more sophisticated analysis of available spatio-temporal and genetic data is likely to yield greater insight in future studies.
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Affiliation(s)
- Rachel Breyta
- Microbiology Oregon State University Corvallis OR USA.,Cary Institute for Ecosystems Studies Millbrook NY USA
| | - Ilana Brito
- Biomedical Engineering Cornell University Ithaca NY USA
| | - Paige Ferguson
- Biological Sciences University of Alabama Tuscaloosa AL USA
| | - Gael Kurath
- US Geological Survey, Western Fisheries Research Center Seattle WA USA
| | - Kerry A Naish
- School of Aquatic and Fisheries Sciences University of Washington Seattle WA USA
| | - Maureen K Purcell
- US Geological Survey, Western Fisheries Research Center Seattle WA USA
| | - Andrew R Wargo
- Department of Aquatic Health Sciences Virginia Institute of Marine Science Gloucester Point VA USA
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10
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Dixon P, Paley R, Alegria-Moran R, Oidtmann B. Epidemiological characteristics of infectious hematopoietic necrosis virus (IHNV): a review. Vet Res 2016; 47:63. [PMID: 27287024 PMCID: PMC4902920 DOI: 10.1186/s13567-016-0341-1] [Citation(s) in RCA: 92] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2015] [Accepted: 04/19/2016] [Indexed: 11/23/2022] Open
Abstract
Infectious hematopoietic necrosis virus (IHNV, Rhabdoviridae), is the causative agent of infectious hematopoietic necrosis (IHN), a disease notifiable to the World Organisation for Animal Health, and various countries and trading areas (including the European Union). IHNV is an economically important pathogen causing clinical disease and mortalities in a wide variety of salmonid species, including the main salmonid species produced in aquaculture, Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss). We reviewed the scientific literature on IHNV on a range of topics, including geographic distribution; host range; conditions required for infection and clinical disease; minimum infectious dose; subclinical infection; shedding of virus by infected fish; transmission via eggs; diagnostic tests; pathogen load and survival of IHNV in host tissues. This information is required for a range of purposes including import risk assessments; parameterisation of disease models; for surveillance planning; and evaluation of the chances of eradication of the pathogen to name just a few. The review focuses on issues that are of relevance for the European context, but many of the data summarised have relevance to IHN globally. Examples for application of the information is presented and data gaps highlighted.
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Affiliation(s)
- Peter Dixon
- Centre for Environment, Fisheries and Aquaculture Science, Weymouth, Dorset, UK
| | - Richard Paley
- Centre for Environment, Fisheries and Aquaculture Science, Weymouth, Dorset, UK
| | - Raul Alegria-Moran
- Faculty of Veterinary and Animal Sciences, University of Chile, Santiago de Chile, Chile
| | - Birgit Oidtmann
- Centre for Environment, Fisheries and Aquaculture Science, Weymouth, Dorset, UK.
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11
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Breyta R, McKenney D, Tesfaye T, Ono K, Kurath G. Increasing virulence, but not infectivity, associated with serially emergent virus strains of a fish rhabdovirus. Virus Evol 2016; 2:vev018. [PMID: 27774291 PMCID: PMC4989874 DOI: 10.1093/ve/vev018] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Surveillance and genetic typing of field isolates of a fish rhabdovirus, infectious hematopoietic necrosis virus (IHNV), has identified four dominant viral genotypes that were involved in serial viral emergence and displacement events in steelhead trout (Oncorhynchus mykiss) in western North America. To investigate drivers of these landscape-scale events, IHNV isolates designated 007, 111, 110, and 139, representing the four relevant genotypes, were compared for virulence and infectivity in controlled laboratory challenge studies in five relevant steelhead trout populations. Viral virulence was assessed as mortality using lethal dose estimates (LD50), survival kinetics, and proportional hazards analysis. A pattern of increasing virulence for isolates 007, 111, and 110 was consistent in all five host populations tested, and correlated with serial emergence and displacements in the virus-endemic lower Columbia River source region during 1980-2013. The fourth isolate, 139, did not have higher virulence than the previous isolate 110. However, the mG139M genotype displayed a conditional displacement phenotype in that it displaced type mG110M in coastal Washington, but not in the lower Columbia River region, indicating that factors other than evolution of higher viral virulence were involved in some displacement events. Viral infectivity, measured as infectious dose (ID50), did not correlate consistently with virulence or with viral emergence, and showed a narrow range of variation relative to the variation observed in virulence. Comparison among the five steelhead trout populations confirmed variation in resistance to IHNV, but correlations with previous history of virus exposure or with sites of viral emergence varied between IHNV source and sink regions. Overall, this study indicated increasing viral virulence over time as a potential driver for emergence and displacement events in the endemic Lower Columbia River source region where these IHNV genotypes originated, but not in adjacent sink regions.
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Affiliation(s)
- Rachel Breyta
- US Geological Survey, Western Fisheries Research Center, 6505 NE 65th St., Seattle, WA 98115 and; School of Aquatic and Fishery Sciences, University of Washington, 1122 NE Boat St., Seattle, WA 98105, USA
| | - Doug McKenney
- US Geological Survey, Western Fisheries Research Center, 6505 NE 65th St., Seattle, WA 98115 and
| | - Tarin Tesfaye
- US Geological Survey, Western Fisheries Research Center, 6505 NE 65th St., Seattle, WA 98115 and
| | - Kotaro Ono
- School of Aquatic and Fishery Sciences, University of Washington, 1122 NE Boat St., Seattle, WA 98105, USA
| | - Gael Kurath
- US Geological Survey, Western Fisheries Research Center, 6505 NE 65th St., Seattle, WA 98115 and
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12
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Kell AM, Wargo AR, Kurath G. Viral fitness does not correlate with three genotype displacement events involving infectious hematopoietic necrosis virus. Virology 2014; 464-465:146-155. [PMID: 25068402 DOI: 10.1016/j.virol.2014.07.003] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2014] [Revised: 06/30/2014] [Accepted: 07/01/2014] [Indexed: 01/11/2023]
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.
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Affiliation(s)
- Alison M Kell
- University of Washington, Seattle, WA, USA; U.S. Geological Survey, Western Fisheries Research Center, Seattle, WA, USA.
| | - Andrew R Wargo
- University of Washington, Seattle, WA, USA; U.S. Geological Survey, Western Fisheries Research Center, Seattle, WA, USA
| | - Gael Kurath
- University of Washington, Seattle, WA, USA; U.S. Geological Survey, Western Fisheries Research Center, Seattle, WA, USA
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13
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Einer-Jensen K, Harmache A, Biacchesi S, Bremont M, Stegmann A, Lorenzen N. High virulence differences among phylogenetically distinct isolates of the fish rhabdovirus viral hemorrhagic septicaemia virus are not explained by variability of the surface glycoprotein G or the non-virion protein Nv. J Gen Virol 2013; 95:307-316. [PMID: 24189623 DOI: 10.1099/vir.0.057448-0] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Viral hemorrhagic septicaemia virus (VHSV) is an important viral pathogen in European rainbow trout farming. Isolates from wild marine fish and freshwater trout farms show highly different virulence profiles: isolates from marine fish species cause little or no mortality in rainbow trout following experimental waterborne challenge, whilst challenge with rainbow trout isolates results in high levels of mortality. Phylogenetic analyses have revealed that the highly virulent trout-derived isolates from freshwater farms have evolved from VHSV isolates from marine fish host species over the past 60 years. Recent isolates from rainbow trout reared in marine zones show intermediate virulence. The present study aimed to identify molecular virulence markers that could be used to classify VHSV isolates according to their ability to cause disease in rainbow trout. By a reverse genetics approach using a VHSV-related novirhabdovirus [infectious hematopoietic necrosis virus (IHNV)], four chimaeric IHNV-VHSV recombinant viruses were generated. These chimaeric viruses included substitution of the IHNV glyco- (G) or non-structural (Nv) protein with their counterparts from either a trout-derived or a marine VHSV strain. Comparative challenge experiments in rainbow trout fingerlings revealed similar levels of survival induced by the recombinant (r)IHNV-VHSV chimaeric viruses regardless of whether the G or Nv genes originated from VHSV isolated from a marine fish species or from rainbow trout. Interestingly, recombinant IHNV gained higher virulence following substitution of the G gene with those of the VHSV strains, whilst the opposite was the case following substitution of the Nv genes.
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Affiliation(s)
| | - Abdallah Harmache
- Unité Infectiologie Animale et santé publique, INRA, 37380 Nouzilly, France
| | - Stéphane Biacchesi
- Unité de Virologie et Immunologie Moléculaires, INRA, Jouy en Josas 78352, France
| | - Michel Bremont
- Unité de Virologie et Immunologie Moléculaires, INRA, Jouy en Josas 78352, France
| | | | - Niels Lorenzen
- Department of Animal Science, Aarhus University, Aarhus, Denmark
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14
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The role of virulence in in vivo superinfection fitness of the vertebrate RNA virus infectious hematopoietic necrosis virus. J Virol 2013; 87:8145-57. [PMID: 23678165 DOI: 10.1128/jvi.00089-13] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
We have developed a novel in vivo superinfection fitness assay to examine superinfection dynamics and the role of virulence in superinfection fitness. This assay involves controlled, sequential infections of a natural vertebrate host, Oncorhynchus mykiss (rainbow trout), with variants of a coevolved viral pathogen, infectious hematopoietic necrosis virus (IHNV). Intervals between infections ranged from 12 h to 7 days, and both frequency of superinfection and viral replication levels were examined. Using virus genotype pairs of equal and unequal virulence, we observed that superinfection generally occurred with decreasing frequency as the interval between exposures to each genotype increased. For both the equal-virulence and unequal-virulence genotype pairs, the frequency of superinfection in most cases was the same regardless of which genotype was used in the primary exposure. The ability to replicate in the context of superinfection also did not differ between the genotypes of equal or unequal virulence tested here. For both genotype pairs, the mean viral load of the secondary virus was significantly reduced in superinfection while primary virus replication was unaffected. Our results demonstrate, for the two genotype pairs examined, that superinfection restriction does occur for IHNV and that higher virulence did not correlate with a significant difference in superinfection fitness. To our knowledge, this is the first assay to examine the role of virulence of an RNA virus in determining superinfection fitness dynamics within a natural vertebrate host.
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15
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Wargo AR, Kurath G. Viral fitness: definitions, measurement, and current insights. Curr Opin Virol 2012; 2:538-45. [PMID: 22986085 PMCID: PMC7102723 DOI: 10.1016/j.coviro.2012.07.007] [Citation(s) in RCA: 90] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2012] [Accepted: 07/24/2012] [Indexed: 11/03/2022]
Abstract
Viral fitness is an active area of research, with recent work involving an expanded number of human, non-human vertebrate, invertebrate, plant, and bacterial viruses. Many publications deal with RNA viruses associated with major disease emergence events, such as HIV-1, influenza virus, and Dengue virus. Study topics include drug resistance, immune escape, viral emergence, host jumps, mutation effects, quasispecies diversity, and mathematical models of viral fitness. Important recent trends include increasing use of in vivo systems to assess vertebrate virus fitness, and a broadening of research beyond replicative fitness to also investigate transmission fitness and epidemiologic fitness. This is essential for a more integrated understanding of overall viral fitness, with implications for disease management in the future.
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Affiliation(s)
- Andrew R Wargo
- US Geological Survey, Western Fisheries Research Center, 6505 NE 65th Street, Seattle, WA 98115, USA
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16
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Lancaster KZ, Pfeiffer JK. Viral population dynamics and virulence thresholds. Curr Opin Microbiol 2012; 15:525-30. [PMID: 22658738 PMCID: PMC3424342 DOI: 10.1016/j.mib.2012.05.007] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2012] [Revised: 05/07/2012] [Accepted: 05/13/2012] [Indexed: 12/17/2022]
Abstract
Viral factors and host barriers influence virally induced disease, and asymptomatic versus symptomatic infection is governed by a 'virulence threshold'. Understanding modulation of virulence thresholds could lend insight into disease outcome and aid in rational therapeutic and vaccine design. RNA viruses are an excellent system to study virulence thresholds in the context of quasispecies population dynamics. RNA viruses have high error frequencies and our understanding of viral population dynamics has been shaped by quasispecies evolutionary theory. In turn, research using RNA viruses as replicons with short generation times and high mutation rates has been an invaluable tool to test models of quasispecies theory. The challenge and new frontier of RNA virus population dynamics research is to combine multiple theoretical models and experimental data to describe viral population behavior as it changes, moving within and between hosts, to predict disease and pathogen emergence. Several excellent studies have begun to undertake this challenge using novel approaches.
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Affiliation(s)
- Karen Z Lancaster
- Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9048, USA
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17
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Wargo AR, Kell AM, Scott RJ, Thorgaard GH, Kurath G. Analysis of host genetic diversity and viral entry as sources of between-host variation in viral load. Virus Res 2012; 165:71-80. [PMID: 22310066 DOI: 10.1016/j.virusres.2012.01.010] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2011] [Revised: 01/21/2012] [Accepted: 01/22/2012] [Indexed: 12/16/2022]
Abstract
Little is known about the factors that drive the high levels of between-host variation in pathogen burden that are frequently observed in viral infections. Here, two factors thought to impact viral load variability, host genetic diversity and stochastic processes linked with viral entry into the host, were examined. This work was conducted with the aquatic vertebrate virus, Infectious hematopoietic necrosis virus (IHNV), in its natural host, rainbow trout. It was found that in controlled in vivo infections of IHNV, a suggestive trend of reduced between-fish viral load variation was observed in a clonal population of isogenic trout compared to a genetically diverse population of out-bred trout. However, this trend was not statistically significant for any of the four viral genotypes examined, and high levels of fish-to-fish variation persisted even in the isogenic trout population. A decrease in fish-to-fish viral load variation was also observed in virus injection challenges that bypassed the host entry step, compared to fish exposed to the virus through the natural water-borne immersion route of infection. This trend was significant for three of the four virus genotypes examined and suggests host entry may play a role in viral load variability. However, high levels of viral load variation also remained in the injection challenges. Together, these results indicate that although host genetic diversity and viral entry may play some role in between-fish viral load variation, they are not major factors. Other biological and non-biological parameters that may influence viral load variation are discussed.
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Affiliation(s)
- Andrew R Wargo
- U.S. Geological Survey, Western Fisheries Research Center, 6505 NE 65th Street, Seattle, WA 98115-5016, USA.
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