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Family Iridoviridae: Molecular and Ecological Studies of a Family...
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Family Iridoviridae: Molecular and Ecological Studies of a Family Infecting Invertebrates and Ectothermic Vertebrates

A special issue of Viruses (ISSN 1999-4915). This special issue belongs to the section "Animal Viruses".

Deadline for manuscript submissions: closed (28 February 2019) | Viewed by 70562

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editors

Prof. Dr. V. Gregory Chinchar

E-Mail Website
Guest Editor
Department of Microbiology and Immunology, University of Mississippi Medical Center, Jackson, MS, USA
Interests: viruses infecting lower vertebrates; specifically Iridoviruses; anti-viral immune responses in cold-blooded vertebrates; viral taxonomy
Special Issues, Collections and Topics in MDPI journals
Assoc. Prof. Dr. Amanda Duffus

E-Mail Website
Guest Editor
Department of Mathematics and Natural Science, Gordon State College, Barnesville, GA 30204, USA
Interests: ranavirus distributions; ranavirus ecology; ranavirus community dynamics; mathematical modelling of ranavirus dynamics; ranavirus phylogenetics

Special Issue Information

Dear Colleagues,

Iridovirids, a generic term describing viruses within the family Iridoviridae, comprise a diverse array of large, icosahedral, double-stranded DNA viruses that infect insects, other invertebrates, and three classes of ectothermic vertebrates (bony fish, reptiles, and amphibians). Iridovirid infections trigger considerable morbidity and have been linked to die-offs among ecologically- and commercially-important fish, reptiles, and amphibians. In this Special Issue of Viruses we will provide a representative sample of current research focused on cellular, molecular and ecological aspects of iridovirid biology. Although clinical disease linked to iridovirid infection, i.e., lymphocystis disease, has been known since the turn of the 20th century, concerted study of iridovirid biology did not begin until Allan Granoff’s identification of frog virus 3 (FV3) in the mid-1960s. Through his efforts and those of others, FV3 became the best characterized member of the family. These studies focused mainly on replicative events in FV3-infected cells and defined the essential elements of virus replication. Although early work was centered primarily on molecular aspects of FV3, research efforts during the last 30 years have expanded to include numerous studies on the ecology of iridovirid infections, replicative events among other species within the genus Ranavirus, as well as other genera within the family, and immune responses to iridovirid infections. Recently, genomic sequence analysis of over 40 members of the family generated a phylogenetically robust basis for our understanding of viral taxonomy and provided a facile way to identify and classify newly identified viruses. In addition, sequence information has provided the basis for numerous studies of viral gene function using siRNA- and antisense morpholino oligonucleotide-mediated knock down, knock out and conditionally-lethal mutants, and ectopic expression studies. Using these approaches, the functions of several viral replicative and immune-modulating proteins have been determined. Moreover, study of virus-encoded immune evasion proteins combined with ongoing research into host anti-viral immunity has provided insights into the evolutionary origins of the vertebrate immune system and may further the development of protective vaccines. The world of iridovirid research has expanded greatly in the last 30 years and we look forward to providing a venue highlighting different facets of research focused on the family Iridoviridae.

Prof. Dr. Gregory Chinchar
Assoc. Prof. Dr. Amanda Duffus
Guest Editors

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Keywords

  • iridovirus
  • Iridoviridae
  • ranavirus
  • viral pathogenesis
  • modeling of infectious disease
  • vaccine development
  • elucidation of viral gene function
  • anti-viral immune responses
  • host-virus interaction
  • viral immune evasion
  • viral ecology

Published Papers (17 papers)

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Editorial

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3 pages, 171 KiB  
Editorial
Molecular and Ecological Studies of a Virus Family (Iridoviridae) Infecting Invertebrates and Ectothermic Vertebrates
by V. Gregory Chinchar and Amanda L. J. Duffus
Viruses 2019, 11(6), 538; https://0-doi-org.brum.beds.ac.uk/10.3390/v11060538 - 09 Jun 2019
Cited by 10 | Viewed by 2283
Abstract
Research involving viruses within the family Iridoviridae (generically designated iridovirids to distinguish members of the family Iridoviridae from members of the genus Iridovirus) has markedly increased in recent years [...] Full article
(This article belongs to the Special Issue Family Iridoviridae: Molecular and Ecological Studies of a Family Infecting Invertebrates and Ectothermic Vertebrates)

Research

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25 pages, 3349 KiB  
Article
Detection and Characterization of Invertebrate Iridoviruses Found in Reptiles and Prey Insects in Europe over the Past Two Decades
by Tibor Papp and Rachel E. Marschang
Viruses 2019, 11(7), 600; https://0-doi-org.brum.beds.ac.uk/10.3390/v11070600 - 02 Jul 2019
Cited by 22 | Viewed by 3776
Abstract
Invertebrate iridoviruses (IIVs), while mostly described in a wide range of invertebrate hosts, have also been repeatedly detected in diagnostic samples from poikilothermic vertebrates including reptiles and amphibians. Since iridoviruses from invertebrate and vertebrate hosts differ strongly from one another based not only [...] Read more.
Invertebrate iridoviruses (IIVs), while mostly described in a wide range of invertebrate hosts, have also been repeatedly detected in diagnostic samples from poikilothermic vertebrates including reptiles and amphibians. Since iridoviruses from invertebrate and vertebrate hosts differ strongly from one another based not only on host range but also on molecular characteristics, a series of molecular studies and bioassays were performed to characterize and compare IIVs from various hosts and evaluate their ability to infect a vertebrate host. Eight IIV isolates from reptilian and orthopteran hosts collected over a period of six years were partially sequenced. Comparison of eight genome portions (total over 14 kbp) showed that these were all very similar to one another and to an earlier described cricket IIV isolate, thus they were given the collective name lizard–cricket IV (Liz–CrIV). One isolate from a chameleon was also subjected to Illumina sequencing and almost the entire genomic sequence was obtained. Comparison of this longer genome sequence showed several differences to the most closely related IIV, Invertebrate iridovirus 6 (IIV6), the type species of the genus Iridovirus, including several deletions and possible recombination sites, as well as insertions of genes of non-iridoviral origin. Three isolates from vertebrate and invertebrate hosts were also used for comparative studies on pathogenicity in crickets (Gryllus bimaculatus) at 20 and 30 °C. Finally, the chameleon isolate used for the genome sequencing studies was also used in a transmission study with bearded dragons. The transmission studies showed large variability in virus replication and pathogenicity of the three tested viruses in crickets at the two temperatures. In the infection study with bearded dragons, lizards inoculated with a Liz–CrIV did not become ill, but the virus was detected in numerous tissues by qPCR and was also isolated in cell culture from several tissues. Highest viral loads were measured in the gastro-intestinal organs and in the skin. These studies demonstrate that Liz–CrIV circulates in the pet trade in Europe. This virus is capable of infecting both invertebrates and poikilothermic vertebrates, although its involvement in disease in the latter has not been proven. Full article
(This article belongs to the Special Issue Family Iridoviridae: Molecular and Ecological Studies of a Family Infecting Invertebrates and Ectothermic Vertebrates)
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11 pages, 1956 KiB  
Article
Ranaviruses Bind Cells from Different Species through Interaction with Heparan Sulfate
by Fei Ke, Zi-Hao Wang, Cheng-Yue Ming and Qi-Ya Zhang
Viruses 2019, 11(7), 593; https://0-doi-org.brum.beds.ac.uk/10.3390/v11070593 - 29 Jun 2019
Cited by 13 | Viewed by 2611
Abstract
Ranavirus cross-species infections have been documented, but the viral proteins involved in the interaction with cell receptors have not yet been identified. Here, viral cell-binding proteins and their cognate cellular receptors were investigated using two ranaviruses, Andrias davidianus ranavirus (ADRV) and Rana grylio [...] Read more.
Ranavirus cross-species infections have been documented, but the viral proteins involved in the interaction with cell receptors have not yet been identified. Here, viral cell-binding proteins and their cognate cellular receptors were investigated using two ranaviruses, Andrias davidianus ranavirus (ADRV) and Rana grylio virus (RGV), and two different cell lines, Chinese giant salamander thymus cells (GSTC) and Epithelioma papulosum cyprinid (EPC) cells. The heparan sulfate (HS) analog heparin inhibited plaque formation of ADRV and RGV in the two cell lines by more than 80% at a concentration of 5 μg/mL. In addition, enzymatic removal of cell surface HS by heparinase I markedly reduced plaque formation by both viruses and competition with heparin reduced virus-cell binding. These results indicate that cell surface HS is involved in ADRV and RGV cell binding and infection. Furthermore, recombinant viral envelope proteins ADRV-58L and RGV-53R bound heparin-Sepharose beads implying the potential that cell surface HS is involved in the initial interaction between ranaviruses and susceptible host cells. To our knowledge, this is the first report identifying cell surface HS as ranavirus binding factor and furthers understanding of interactions between ranaviruses and host cells. Full article
(This article belongs to the Special Issue Family Iridoviridae: Molecular and Ecological Studies of a Family Infecting Invertebrates and Ectothermic Vertebrates)
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13 pages, 2481 KiB  
Article
Modelling Ranavirus Transmission in Populations of Common Frogs (Rana temporaria) in the United Kingdom
by Amanda L.J. Duffus, Trenton W.J. Garner, Richard A. Nichols, Joshua P. Standridge and Julia E. Earl
Viruses 2019, 11(6), 556; https://0-doi-org.brum.beds.ac.uk/10.3390/v11060556 - 15 Jun 2019
Cited by 6 | Viewed by 3723
Abstract
Ranaviruses began emerging in common frogs (Rana temporaria) in the United Kingdom in the late 1980s and early 1990s, causing severe disease and declines in the populations of these animals. Herein, we explored the transmission dynamics of the ranavirus(es) present in [...] Read more.
Ranaviruses began emerging in common frogs (Rana temporaria) in the United Kingdom in the late 1980s and early 1990s, causing severe disease and declines in the populations of these animals. Herein, we explored the transmission dynamics of the ranavirus(es) present in common frog populations, in the context of a simple susceptible-infected (SI) model, using parameters derived from the literature. We explored the effects of disease-induced population decline on the dynamics of the ranavirus. We then extended the model to consider the infection dynamics in populations exposed to both ulcerative and hemorrhagic forms of the ranaviral disease. The preliminary investigation indicated the important interactions between the forms. When the ulcerative form was present in a population and the hemorrhagic form was later introduced, the hemorrhagic form of the disease needed to be highly contagious, to persist. We highlighted the areas where further research and experimental evidence is needed and hope that these models would act as a guide for further research into the amphibian disease dynamics. Full article
(This article belongs to the Special Issue Family Iridoviridae: Molecular and Ecological Studies of a Family Infecting Invertebrates and Ectothermic Vertebrates)
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10 pages, 783 KiB  
Article
Artemia spp., a Susceptible Host and Vector for Lymphocystis Disease Virus
by Estefania J. Valverde, Alejandro M. Labella, Juan J. Borrego and Dolores Castro
Viruses 2019, 11(6), 506; https://0-doi-org.brum.beds.ac.uk/10.3390/v11060506 - 01 Jun 2019
Cited by 10 | Viewed by 2863
Abstract
Different developmental stages of Artemia spp. (metanauplii, juveniles and adults) were bath-challenged with two isolates of the Lymphocystis disease virus (LCDV), namely, LCDV SA25 (belonging to the species Lymphocystis disease virus 3) and ATCC VR-342 (an unclassified member of the genus Lymphocystivirus [...] Read more.
Different developmental stages of Artemia spp. (metanauplii, juveniles and adults) were bath-challenged with two isolates of the Lymphocystis disease virus (LCDV), namely, LCDV SA25 (belonging to the species Lymphocystis disease virus 3) and ATCC VR-342 (an unclassified member of the genus Lymphocystivirus). Viral quantification and gene expression were analyzed by qPCR at different times post-inoculation (pi). In addition, infectious titres were determined at 8 dpi by integrated cell culture (ICC)-RT-PCR, an assay that detects viral mRNA in inoculated cell cultures. In LCDV-challenged Artemia, the viral load increased by 2–3 orders of magnitude (depending on developmental stage and viral isolate) during the first 8–12 dpi, with viral titres up to 2.3 × 102 Most Probable Number of Infectious Units (MPNIU)/mg. Viral transcripts were detected in the infected Artemia, relative expression values showed a similar temporal evolution in the different experimental groups. Moreover, gilthead seabream (Sparus aurata) fingerlings were challenged by feeding on LCDV-infected metanauplii. Although no Lymphocystis symptoms were observed in the fish, the number of viral DNA copies was significantly higher at the end of the experimental trial and major capsid protein (mcp) gene expression was consistently detected. The results obtained support that LCDV infects Artemia spp., establishing an asymptomatic productive infection at least under the experimental conditions tested, and that the infected metanauplii are a vector for LCDV transmission to gilthead seabream. Full article
(This article belongs to the Special Issue Family Iridoviridae: Molecular and Ecological Studies of a Family Infecting Invertebrates and Ectothermic Vertebrates)
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10 pages, 2382 KiB  
Article
Characterization of a Novel Megalocytivirus Isolated from European Chub (Squalius cephalus)
by Maya A. Halaly, Kuttichantran Subramaniam, Samantha A. Koda, Vsevolod L. Popov, David Stone, Keith Way and Thomas B. Waltzek
Viruses 2019, 11(5), 440; https://0-doi-org.brum.beds.ac.uk/10.3390/v11050440 - 15 May 2019
Cited by 14 | Viewed by 4187
Abstract
A novel virus from moribund European chub (Squalius cephalus) was isolated on epithelioma papulosum cyprini (EPC) cells. Transmission electron microscopic examination revealed abundant non-enveloped, hexagonal virus particles in the cytoplasm of infected EPC cells consistent with an iridovirus. Illumina MiSeq sequence [...] Read more.
A novel virus from moribund European chub (Squalius cephalus) was isolated on epithelioma papulosum cyprini (EPC) cells. Transmission electron microscopic examination revealed abundant non-enveloped, hexagonal virus particles in the cytoplasm of infected EPC cells consistent with an iridovirus. Illumina MiSeq sequence data enabled the assembly and annotation of the full genome (128,216 bp encoding 108 open reading frames) of the suspected iridovirus. Maximum Likelihood phylogenetic analyses based on 25 iridovirus core genes supported the European chub iridovirus (ECIV) as being the sister species to the recently-discovered scale drop disease virus (SDDV), which together form the most basal megalocytivirus clade. Genetic analyses of the ECIV major capsid protein and ATPase genes revealed the greatest nucleotide identity to members of the genus Megalocytivirus including SDDV. These data support ECIV as a novel member within the genus Megalocytivirus. Experimental challenge studies are needed to fulfill River’s postulates and determine whether ECIV induces the pathognomonic microscopic lesions (i.e., megalocytes with basophilic cytoplasmic inclusions) observed in megalocytivirus infections. Full article
(This article belongs to the Special Issue Family Iridoviridae: Molecular and Ecological Studies of a Family Infecting Invertebrates and Ectothermic Vertebrates)
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13 pages, 4459 KiB  
Article
Interaction between Two Iridovirus Core Proteins and Their Effects on Ranavirus (RGV) Replication in Cells from Different Species
by Xiao-Tao Zeng and Qi-Ya Zhang
Viruses 2019, 11(5), 416; https://0-doi-org.brum.beds.ac.uk/10.3390/v11050416 - 04 May 2019
Cited by 12 | Viewed by 3107
Abstract
The two putative proteins RGV-63R and RGV-91R encoded by Rana grylio virus (RGV) are DNA polymerase and proliferating cell nuclear antigen (PCNA) respectively, and are core proteins of iridoviruses. Here, the interaction between RGV-63R and RGV-91R was detected by a yeast two-hybrid (Y2H) [...] Read more.
The two putative proteins RGV-63R and RGV-91R encoded by Rana grylio virus (RGV) are DNA polymerase and proliferating cell nuclear antigen (PCNA) respectively, and are core proteins of iridoviruses. Here, the interaction between RGV-63R and RGV-91R was detected by a yeast two-hybrid (Y2H) assay and further confirmed by co-immunoprecipitation (co-IP) assays. Subsequently, RGV-63R or RGV-91R were expressed alone or co-expressed in two kinds of aquatic animal cells including amphibian Chinese giant salamander thymus cells (GSTCs) and fish Epithelioma papulosum cyprinid cells (EPCs) to investigate their localizations and effects on RGV genome replication. The results showed that their localizations in the two kinds of cells are consistent. RGV-63R localized in the cytoplasm, while RGV-91R localized in the nucleus. However, when co-expressed, RGV-63R localized in both the cytoplasm and the nucleus, and colocalized with RGV-91R in the nucleus. 91R△NLS represents the RGV-91R deleting nuclear localization signal, which is localized in the cytoplasm and colocalized with RGV-63R in the cytoplasm. qPCR analysis revealed that sole expression and co-expression of the two proteins in the cells of two species significantly promoted RGV genome replication, while varying degrees of viral genome replication levels may be linked to the cell types. This study provides novel molecular evidence for ranavirus cross-species infection and replication. Full article
(This article belongs to the Special Issue Family Iridoviridae: Molecular and Ecological Studies of a Family Infecting Invertebrates and Ectothermic Vertebrates)
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15 pages, 2213 KiB  
Article
IIV-6 Inhibits NF-κB Responses in Drosophila
by Cara West, Florentina Rus, Ying Chen, Anni Kleino, Monique Gangloff, Don B. Gammon and Neal Silverman
Viruses 2019, 11(5), 409; https://0-doi-org.brum.beds.ac.uk/10.3390/v11050409 - 01 May 2019
Cited by 10 | Viewed by 4914
Abstract
The host immune response and virus-encoded immune evasion proteins pose constant, mutual selective pressure on each other. Virally encoded immune evasion proteins also indicate which host pathways must be inhibited to allow for viral replication. Here, we show that IIV-6 is capable of [...] Read more.
The host immune response and virus-encoded immune evasion proteins pose constant, mutual selective pressure on each other. Virally encoded immune evasion proteins also indicate which host pathways must be inhibited to allow for viral replication. Here, we show that IIV-6 is capable of inhibiting the two Drosophila NF-κB signaling pathways, Imd and Toll. Antimicrobial peptide (AMP) gene induction downstream of either pathway is suppressed when cells infected with IIV-6 are also stimulated with Toll or Imd ligands. We find that cleavage of both Imd and Relish, as well as Relish nuclear translocation, three key points in Imd signal transduction, occur in IIV-6 infected cells, indicating that the mechanism of viral inhibition is farther downstream, at the level of Relish promoter binding or transcriptional activation. Additionally, flies co-infected with both IIV-6 and the Gram-negative bacterium, Erwinia carotovora carotovora, succumb to infection more rapidly than flies singly infected with either the virus or the bacterium. These findings demonstrate how pre-existing infections can have a dramatic and negative effect on secondary infections, and establish a Drosophila model to study confection susceptibility. Full article
(This article belongs to the Special Issue Family Iridoviridae: Molecular and Ecological Studies of a Family Infecting Invertebrates and Ectothermic Vertebrates)
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12 pages, 355 KiB  
Article
Evaluating the Within-Host Dynamics of Ranavirus Infection with Mechanistic Disease Models and Experimental Data
by Joseph R. Mihaljevic, Amy L. Greer and Jesse L. Brunner
Viruses 2019, 11(5), 396; https://0-doi-org.brum.beds.ac.uk/10.3390/v11050396 - 27 Apr 2019
Cited by 3 | Viewed by 3172
Abstract
Mechanistic models are critical for our understanding of both within-host dynamics (i.e., pathogen replication and immune system processes) and among-host dynamics (i.e., transmission). Within-host models, however, are not often fit to experimental data, which can serve as a robust method of hypothesis testing [...] Read more.
Mechanistic models are critical for our understanding of both within-host dynamics (i.e., pathogen replication and immune system processes) and among-host dynamics (i.e., transmission). Within-host models, however, are not often fit to experimental data, which can serve as a robust method of hypothesis testing and hypothesis generation. In this study, we use mechanistic models and empirical, time-series data of viral titer to better understand the replication of ranaviruses within their amphibian hosts and the immune dynamics that limit viral replication. Specifically, we fit a suite of potential models to our data, where each model represents a hypothesis about the interactions between viral replication and immune defense. Through formal model comparison, we find a parsimonious model that captures key features of our time-series data: The viral titer rises and falls through time, likely due to an immune system response, and that the initial viral dosage affects both the peak viral titer and the timing of the peak. Importantly, our model makes several predictions, including the existence of long-term viral infections, which can be validated in future studies. Full article
(This article belongs to the Special Issue Family Iridoviridae: Molecular and Ecological Studies of a Family Infecting Invertebrates and Ectothermic Vertebrates)
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15 pages, 3646 KiB  
Article
Susceptibility of Exopalaemon carinicauda to the Infection with Shrimp Hemocyte Iridescent Virus (SHIV 20141215), a Strain of Decapod Iridescent Virus 1 (DIV1)
by Xing Chen, Liang Qiu, Hailiang Wang, Peizhuo Zou, Xuan Dong, Fuhua Li and Jie Huang
Viruses 2019, 11(4), 387; https://0-doi-org.brum.beds.ac.uk/10.3390/v11040387 - 25 Apr 2019
Cited by 51 | Viewed by 6588
Abstract
In this study, ridgetail white prawns—Exopalaemon carinicauda—were infected per os (PO) with debris of Penaeus vannamei infected with shrimp hemocyte iridescent virus (SHIV 20141215), a strain of decapod iridescent virus 1 (DIV1), and via intramuscular injection (IM with raw extracts of [...] Read more.
In this study, ridgetail white prawns—Exopalaemon carinicauda—were infected per os (PO) with debris of Penaeus vannamei infected with shrimp hemocyte iridescent virus (SHIV 20141215), a strain of decapod iridescent virus 1 (DIV1), and via intramuscular injection (IM with raw extracts of SHIV 20141215. The infected E. carinicauda showed obvious clinical symptoms, including weakness, empty gut and stomach, pale hepatopancreas, and partial death with mean cumulative mortalities of 42.5% and 70.8% by nonlinear regression, respectively. Results of TaqMan probe-based real-time quantitative PCR showed that the moribund and surviving individuals with clinical signs of infected E. carinicauda were DIV1-positive. Histological examination showed that there were darkly eosinophilic and cytoplasmic inclusions, of which some were surrounded with or contained tiny basophilic staining, and pyknosis in hemocytes in hepatopancreatic sinus, hematopoietic cells, cuticular epithelium, etc. On the slides of in situ DIG-labeling-loop-mediated DNA amplification (ISDL), positive signals were observed in hematopoietic tissue, stomach, cuticular epithelium, and hepatopancreatic sinus of infected prawns from both PO and IM groups. Transmission electron microscopy (TEM) of ultrathin sections showed that icosahedral DIV1 particles existed in hepatopancreatic sinus and gills of the infected E. carinicauda from the PO group. The viral particles were also observed in hepatopancreatic sinus, gills, pereiopods, muscles, and uropods of the infected E. carinicauda from the IM group. The assembled virions, which mostly distributed along the edge of the cytoplasmic virogenic stromata near cellular membrane of infected cells, were enveloped and approximately 150 nm in diameter. The results of molecular tests, histopathological examination, ISDL, and TEM confirmed that E. carinicauda is a susceptible host of DIV1. This study also indicated that E. carinicauda showed some degree of tolerance to the infection with DIV1 per os challenge mimicking natural pathway. Full article
(This article belongs to the Special Issue Family Iridoviridae: Molecular and Ecological Studies of a Family Infecting Invertebrates and Ectothermic Vertebrates)
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16 pages, 3506 KiB  
Article
Distribution and Phylogeny of Erythrocytic Necrosis Virus (ENV) in Salmon Suggests Marine Origin
by Veronica A. Pagowski, Gideon J. Mordecai, Kristina M. Miller, Angela D. Schulze, Karia H. Kaukinen, Tobi J. Ming, Shaorong Li, Amy K. Teffer, Amy Tabata and Curtis A. Suttle
Viruses 2019, 11(4), 358; https://0-doi-org.brum.beds.ac.uk/10.3390/v11040358 - 18 Apr 2019
Cited by 8 | Viewed by 3960
Abstract
Viral erythrocytic necrosis (VEN) affects over 20 species of marine and anadromous fishes in the North Atlantic and North Pacific Oceans. However, the distribution and strain variation of its viral causative agent, erythrocytic necrosis virus (ENV), has not been well characterized within Pacific [...] Read more.
Viral erythrocytic necrosis (VEN) affects over 20 species of marine and anadromous fishes in the North Atlantic and North Pacific Oceans. However, the distribution and strain variation of its viral causative agent, erythrocytic necrosis virus (ENV), has not been well characterized within Pacific salmon. Here, metatranscriptomic sequencing of Chinook salmon revealed that ENV infecting salmon was closely related to ENV from Pacific herring, with inferred amino-acid sequences from Chinook salmon being 99% identical to those reported for herring. Sequence analysis also revealed 89 protein-encoding sequences attributed to ENV, greatly expanding the amount of genetic information available for this virus. High-throughput PCR of over 19,000 fish showed that ENV is widely distributed in the NE Pacific Ocean and was detected in 12 of 16 tested species, including in 27% of herring, 38% of anchovy, 17% of pollock, and 13% of sand lance. Despite frequent detection in marine fish, ENV prevalence was significantly lower in fish from freshwater (0.03%), as assessed with a generalized linear mixed effects model (p = 5.5 × 10−8). Thus, marine fish are likely a reservoir for the virus. High genetic similarity between ENV obtained from salmon and herring also suggests that transmission between these hosts is likely. Full article
(This article belongs to the Special Issue Family Iridoviridae: Molecular and Ecological Studies of a Family Infecting Invertebrates and Ectothermic Vertebrates)
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14 pages, 3509 KiB  
Article
Description of a Natural Infection with Decapod Iridescent Virus 1 in Farmed Giant Freshwater Prawn, Macrobrachium rosenbergii
by Liang Qiu, Xing Chen, Ruo-Heng Zhao, Chen Li, Wen Gao, Qing-Li Zhang and Jie Huang
Viruses 2019, 11(4), 354; https://0-doi-org.brum.beds.ac.uk/10.3390/v11040354 - 17 Apr 2019
Cited by 70 | Viewed by 8720
Abstract
Macrobrachium rosenbergii is a valuable freshwater prawn in Asian aquaculture. In recent years, a new symptom that was generally called “white head” has caused high mortality in M. rosenbergii farms in China. Samples of M. rosenbergii, M. nipponense, Procambarus clarkii, [...] Read more.
Macrobrachium rosenbergii is a valuable freshwater prawn in Asian aquaculture. In recent years, a new symptom that was generally called “white head” has caused high mortality in M. rosenbergii farms in China. Samples of M. rosenbergii, M. nipponense, Procambarus clarkii, M. superbum, Penaeus vannamei, and Cladocera from a farm suffering from white head in Jiangsu Province were collected and analyzed in this study. Pathogen detection showed that all samples were positive for Decapod iridescent virus 1 (DIV1). Histopathological examination revealed dark eosinophilic inclusions and pyknosis in hematopoietic tissue, hepatopancreas, and gills of M. rosenbergii and M. nipponense. Blue signals of in situ digoxigenin-labeled loop-mediated isothermal amplification appeared in hematopoietic tissue, hemocytes, hepatopancreatic sinus, and antennal gland. Transmission electron microscopy of ultrathin sections showed a large number of DIV1 particles with a mean diameter about 157.9 nm. The virogenic stromata and budding virions were observed in hematopoietic cells. Quantitative detection with TaqMan probe based real-time PCR of different tissues in naturally infected M. rosenbergii showed that hematopoietic tissue contained the highest DIV1 load with a relative abundance of 25.4 ± 16.9%. Hepatopancreas and muscle contained the lowest DIV1 loads with relative abundances of 2.44 ± 1.24% and 2.44 ± 2.16%, respectively. The above results verified that DIV1 is the pathogen causing white head in M. rosenbergii. M. nipponense and Pr. clarkii are also species susceptible to DIV1. Full article
(This article belongs to the Special Issue Family Iridoviridae: Molecular and Ecological Studies of a Family Infecting Invertebrates and Ectothermic Vertebrates)
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14 pages, 6251 KiB  
Article
Critical Role of an MHC Class I-Like/Innate-Like T Cell Immune Surveillance System in Host Defense against Ranavirus (Frog Virus 3) Infection
by Eva-Stina Isabella Edholm, Francisco De Jesús Andino, Jinyeong Yim, Katherine Woo and Jacques Robert
Viruses 2019, 11(4), 330; https://0-doi-org.brum.beds.ac.uk/10.3390/v11040330 - 06 Apr 2019
Cited by 11 | Viewed by 2952
Abstract
Besides the central role of classical Major Histocompatibility Complex (MHC) class Ia-restricted conventional Cluster of Differentiation 8 (CD8) T cells in antiviral host immune response, the amphibian Xenopus laevis critically rely on MHC class I-like (mhc1b10.1.L or XNC10)-restricted innate-like (i)T cells (iVα6 T [...] Read more.
Besides the central role of classical Major Histocompatibility Complex (MHC) class Ia-restricted conventional Cluster of Differentiation 8 (CD8) T cells in antiviral host immune response, the amphibian Xenopus laevis critically rely on MHC class I-like (mhc1b10.1.L or XNC10)-restricted innate-like (i)T cells (iVα6 T cells) to control infection by the ranavirus Frog virus 3 (FV3). To complement and extend our previous reverse genetic studies showing that iVα6 T cells are required for tadpole survival, as well as for timely and effective adult viral clearance, we examined the conditions and kinetics of iVα6 T cell response against FV3. Using a FV3 knock-out (KO) growth-defective mutant, we found that upregulation of the XNC10 restricting class I-like gene and the rapid recruitment of iVα6 T cells depend on detectable viral replication and productive FV3 infection. In addition, by in vivo depletion with XNC10 tetramers, we demonstrated the direct antiviral effector function of iVα6 T cells. Notably, the transitory iVα6 T cell defect delayed innate interferon and cytokine gene response, resulting in long-lasting negative inability to control FV3 infection. These findings suggest that in Xenopus and likely other amphibians, an immune surveillance system based on the early activation of iT cells by non-polymorphic MHC class-I like molecules is important for efficient antiviral immune response. Full article
(This article belongs to the Special Issue Family Iridoviridae: Molecular and Ecological Studies of a Family Infecting Invertebrates and Ectothermic Vertebrates)
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15 pages, 2455 KiB  
Article
Geographic Distribution of Epizootic haematopoietic necrosis virus (EHNV) in Freshwater Fish in South Eastern Australia: Lost Opportunity for a Notifiable Pathogen to Expand Its Geographic Range
by Joy A. Becker, Dean Gilligan, Martin Asmus, Alison Tweedie and Richard J. Whittington
Viruses 2019, 11(4), 315; https://0-doi-org.brum.beds.ac.uk/10.3390/v11040315 - 01 Apr 2019
Cited by 3 | Viewed by 3592
Abstract
Epizootic haematopoietic necrosis virus (EHNV) was originally detected in Victoria, Australia in 1984. It spread rapidly over two decades with epidemic mortality events in wild redfin perch (Perca fluviatilis) and mild disease in farmed rainbow trout (Oncorhynchus mykiss) being [...] Read more.
Epizootic haematopoietic necrosis virus (EHNV) was originally detected in Victoria, Australia in 1984. It spread rapidly over two decades with epidemic mortality events in wild redfin perch (Perca fluviatilis) and mild disease in farmed rainbow trout (Oncorhynchus mykiss) being documented across southeastern Australia in New South Wales (NSW), the Australian Capital Territory (ACT), Victoria, and South Australia. We conducted a survey for EHNV between July 2007 and June 2011. The disease occurred in juvenile redfin perch in ACT in December 2008, and in NSW in December 2009 and December 2010. Based on testing 3622 tissue and 492 blood samples collected from fish across southeastern Australia, it was concluded that EHNV was most likely absent from redfin perch outside the endemic area in the upper Murrumbidgee River catchment in the Murray–Darling Basin (MDB), and it was not detected in other fish species. The frequency of outbreaks in redfin perch has diminished over time, and there have been no reports since 2012. As the disease is notifiable and a range of fish species are known to be susceptible to EHNV, existing policies to reduce the likelihood of spreading out of the endemic area are justified. Full article
(This article belongs to the Special Issue Family Iridoviridae: Molecular and Ecological Studies of a Family Infecting Invertebrates and Ectothermic Vertebrates)
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15 pages, 7414 KiB  
Article
Pathogen Risk Analysis for Wild Amphibian Populations Following the First Report of a Ranavirus Outbreak in Farmed American Bullfrogs (Lithobates catesbeianus) from Northern Mexico
by Bernardo Saucedo, José M. Serrano, Mónica Jacinto-Maldonado, Rob S. E. W. Leuven, Abraham A. Rocha García, Adriana Méndez Bernal, Andrea Gröne, Steven J. Van Beurden and César M. Escobedo-Bonilla
Viruses 2019, 11(1), 26; https://0-doi-org.brum.beds.ac.uk/10.3390/v11010026 - 03 Jan 2019
Cited by 15 | Viewed by 5088
Abstract
Ranaviruses are the second deadliest pathogens for amphibian populations throughout the world. Despite their wide distribution in America, these viruses have never been reported in Mexico, the country with the fifth highest amphibian diversity in the world. This paper is the first to [...] Read more.
Ranaviruses are the second deadliest pathogens for amphibian populations throughout the world. Despite their wide distribution in America, these viruses have never been reported in Mexico, the country with the fifth highest amphibian diversity in the world. This paper is the first to address an outbreak of ranavirus in captive American bullfrogs (Lithobates catesbeianus) from Sinaloa, Mexico. The farm experienced high mortality in an undetermined number of juveniles and sub-adult bullfrogs. Affected animals displayed clinical signs and gross lesions such as lethargy, edema, skin ulcers, and hemorrhages consistent with ranavirus infection. The main microscopic lesions included mild renal tubular necrosis and moderate congestion in several organs. Immunohistochemical analyses revealed scant infected hepatocytes and renal tubular epithelial cells. Phylogenetic analysis of five partial ranavirus genes showed that the causative agent clustered within the Frog virus 3 clade. Risk assessment with the Pandora+ protocol demonstrated a high risk for the pathogen to affect amphibians from neighboring regions (overall Pandora risk score: 0.619). Given the risk of American bullfrogs escaping and spreading the disease to wild amphibians, efforts should focus on implementing effective containment strategies and surveillance programs for ranavirus at facilities undertaking intensive farming of amphibians. Full article
(This article belongs to the Special Issue Family Iridoviridae: Molecular and Ecological Studies of a Family Infecting Invertebrates and Ectothermic Vertebrates)
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15 pages, 1053 KiB  
Technical Note
eDNA Increases the Detectability of Ranavirus Infection in an Alpine Amphibian Population
by Claude Miaud, Véronique Arnal, Marie Poulain, Alice Valentini and Tony Dejean
Viruses 2019, 11(6), 526; https://0-doi-org.brum.beds.ac.uk/10.3390/v11060526 - 06 Jun 2019
Cited by 33 | Viewed by 5222
Abstract
The early detection and identification of pathogenic microorganisms is essential in order to deploy appropriate mitigation measures. Viruses in the Iridoviridae family, such as those in the Ranavirus genus, can infect amphibian species without resulting in mortality or clinical signs, and they can [...] Read more.
The early detection and identification of pathogenic microorganisms is essential in order to deploy appropriate mitigation measures. Viruses in the Iridoviridae family, such as those in the Ranavirus genus, can infect amphibian species without resulting in mortality or clinical signs, and they can also infect other hosts than amphibian species. Diagnostic techniques allowing the detection of the pathogen outside the period of host die-off would thus be of particular use. In this study, we tested a method using environmental DNA (eDNA) on a population of common frogs (Rana temporaria) known to be affected by a Ranavirus in the southern Alps in France. In six sampling sessions between June and September (the species’ activity period), we collected tissue samples from dead and live frogs (adults and tadpoles), as well as insects (aquatic and terrestrial), sediment, and water. At the beginning of the breeding season in June, one adult was found dead; at the end of July, a mass mortality of tadpoles was observed. The viral DNA was detected in both adults and tadpoles (dead or alive) and in water samples, but it was not detected in insects or sediment. In live frog specimens, the virus was detected from June to September and in water samples from August to September. Dead tadpoles that tested positive for Ranavirus were observed only on one date (at the end of July). Our results indicate that eDNA can be an effective alternative to tissue/specimen sampling and can detect Ranavirus presence outside die-offs. Another advantage is that the collection of water samples can be performed by most field technicians. This study confirms that the use of eDNA can increase the performance and accuracy of wildlife health status monitoring and thus contribute to more effective surveillance programs. Full article
(This article belongs to the Special Issue Family Iridoviridae: Molecular and Ecological Studies of a Family Infecting Invertebrates and Ectothermic Vertebrates)
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8 pages, 1821 KiB  
Brief Report
Localization of Frog Virus 3 Conserved Viral Proteins 88R, 91R, and 94L
by Emily Penny and Craig R. Brunetti
Viruses 2019, 11(3), 276; https://0-doi-org.brum.beds.ac.uk/10.3390/v11030276 - 19 Mar 2019
Cited by 2 | Viewed by 2736
Abstract
The characterization of the function of conserved viral genes is central to developing a greater understanding of important aspects of viral replication or pathogenesis. A comparative genomic analysis of the iridoviral genomes identified 26 core genes conserved across the family Iridoviridae. Three [...] Read more.
The characterization of the function of conserved viral genes is central to developing a greater understanding of important aspects of viral replication or pathogenesis. A comparative genomic analysis of the iridoviral genomes identified 26 core genes conserved across the family Iridoviridae. Three of those conserved genes have no defined function; these include the homologs of frog virus 3 (FV3) open reading frames (ORFs) 88R, 91R, and 94L. Conserved viral genes that have been previously identified are known to participate in a number of viral activities including: transcriptional regulation, DNA replication/repair/modification/processing, protein modification, and viral structural proteins. To begin to characterize the conserved FV3 ORFs 88R, 91R, and 94L, we cloned the genes and determined their intracellular localization. We demonstrated that 88R localizes to the cytoplasm of the cell while 91R localizes to the nucleus and 94L localizes to the endoplasmic reticulum (ER). Full article
(This article belongs to the Special Issue Family Iridoviridae: Molecular and Ecological Studies of a Family Infecting Invertebrates and Ectothermic Vertebrates)
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