James K. Jancovich

Bio: James K. Jancovich is an academic researcher from California State University San Marcos. The author has contributed to research in topics: Ranavirus & Iridoviridae. The author has an hindex of 6, co-authored 8 publications receiving 179 citations. Previous affiliations of James K. Jancovich include California State University.

ICTV Virus Taxonomy Profile: Iridoviridae.

Abstract: The Iridoviridae is a family of large, icosahedral viruses with double-stranded DNA genomes ranging in size from 103 to 220 kbp. Members of the subfamily Alphairidovirinae infect ectothermic vertebrates (bony fish, amphibians and reptiles), whereas members of the subfamily Betairidovirinae mainly infect insects and crustaceans. Infections can be either covert or patent, and in vertebrates they can lead to high levels of mortality among commercially and ecologically important fish and amphibians. This is a summary of the current International Committee on Taxonomy of Viruses (ICTV) Report on the taxonomy of the Iridoviridae, which is available at www.ictv.global/report/iridoviridae.

Ranavirus Taxonomy and Phylogeny

Abstract: Ranaviruses (genus Ranavirus, family Iridoviridae) are large double-stranded DNA (dsDNA) viruses that infect economically and ecologically important cold-blooded vertebrates worldwide. Taxonomically, ranaviruses belong to a monophyletic group of viruses referred to as the Nucleocytoplasmic Large DNA Viruses (NCLDV). The NCLDV cluster contains viruses with the largest known viral genomes and infects a diverse array of eukaryotic hosts. The family Iridoviridae is currently divided into five genera: Iridovirus, Chloriridovirus, Megalocytivirus, Lymphocystivirus, and Ranavirus. Ranavirus taxonomy is based on restriction endonuclease fragment length polymorphism (RFLP) profiles of genomic DNA, virus protein profiles, DNA sequence analysis, and host specificity as well as whole genome dot plot analysis and phylogenetic analysis of individual and concatenated gene sequences. In this chapter, we discuss the current taxonomy of the genus Ranavirus as well as the phylogenetic relationship among currently identified ranaviruses. In addition, we discuss the future of ranavirus taxonomy in light of current phylogenetic analyses.

Ranavirus Replication: Molecular, Cellular, and Immunological Events

Abstract: The spatially compartmentalized replication strategy of ranaviruses and other members of the family Iridoviridae is unique among DNA viruses and is a hallmark of the family. Viral DNA replication initially takes place within the nucleus and results in the formation of genome-sized molecules. Subsequently, viral DNA is transported into the cytoplasm wherein a second round of DNA synthesis takes place in which concatemers 10–20-times the size of the viral genome are generated. As with viral DNA synthesis, viral RNA synthesis shows a similar compartmentalization: early transcription takes place within the nucleus in reactions catalyzed by host RNA polymerase II, whereas late viral transcription occurs within the cytoplasm in reactions catalyzed by a virus-encoded transcriptase. Morphologically distinct viral assembly sites form within the cytoplasm and viral DNA is packaged into virus particles by a headful mechanism resulting in genomes that are circularly permuted and terminally redundant. Although the outlines of viral metabolism and virion assembly are known, the functions of specific viral gene products remain to be elucidated. Recent attempts at understanding the precise role of viral proteins in these and other events within virus-infected cells are ongoing and have utilized a variety of contemporary approaches including gene knock down mediated by antisense morpholino oligonucleotides and RNA interference, knock out and conditionally lethal mutants, and ectopic expression of recombinant viral proteins.

Recombinant Ranaviruses for Studying Evolution of Host–Pathogen Interactions in Ectothermic Vertebrates

Abstract: Ranaviruses (Iridoviridae) are large DNA viruses that are causing emerging infectious diseases at an alarming rate in both wild and captive cold blood vertebrate species all over the world. Although the general biology of these viruses that presents some similarities with poxvirus is characterized, many aspects of their replication cycles, host cell interactions and evolution still remain largely unclear, especially in vivo. Over several years, strategies to generate site-specific ranavirus recombinant, either expressing fluorescent reporter genes or deficient for particular viral genes, have been developed. We review here these strategies, the main ranavirus recombinants characterized and their usefulness for in vitro and in vivo studies.

Distribution and Host Range of Ranaviruses

Abstract: Ranaviruses are globally distributed pathogens in amphibian, fish, and reptile communities that appear to be emerging. Cases of ranavirus infection or disease have been confirmed in at least 105 amphibian species (18 families), 41 fish species (22 families), and 29 reptile species (12 families). Ranaviruses have been documented on all continents except Antarctica, and are frequently associated with mass die-offs. Host susceptibility differs among species, with some species harboring subclinical infections and likely serving as reservoirs for the virus, and other highly susceptible species amplifying the virus. Currently, there are six recognized species of ranavirus, and all are not equally pathogenic among hosts. Frog virus 3 (FV3) is the type species of the genus Ranavirus, and appears to be the most globally distributed species infecting ectothermic taxonomic across three vertebrate classes. International commerce involving subclinically infected ectothermic vertebrates undoubtedly has contributed to the global distribution and emergence of ranaviruses. Herein, we describe the global distributed species infecting ectothermic vertebrates across three taxonomic classes.

ICTV Virus Taxonomy Profile: Iridoviridae.

Abstract: The Iridoviridae is a family of large, icosahedral viruses with double-stranded DNA genomes ranging in size from 103 to 220 kbp. Members of the subfamily Alphairidovirinae infect ectothermic vertebrates (bony fish, amphibians and reptiles), whereas members of the subfamily Betairidovirinae mainly infect insects and crustaceans. Infections can be either covert or patent, and in vertebrates they can lead to high levels of mortality among commercially and ecologically important fish and amphibians. This is a summary of the current International Committee on Taxonomy of Viruses (ICTV) Report on the taxonomy of the Iridoviridae, which is available at www.ictv.global/report/iridoviridae.

Description of a Natural Infection with Decapod Iridescent Virus 1 in Farmed Giant Freshwater Prawn, Macrobrachium rosenbergii.

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, 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.

Comparative Pathology of Ranaviruses and Diagnostic Techniques

Abstract: Recognizing the pathological changes caused by ranaviruses, understanding how to properly collect test samples, and knowing what diagnostic tools to choose are key to detecting ranaviruses and in determining whether they are a factor in morbidity and mortality events. Whether infection occurs in fish, reptiles, or amphibians, clinical disease is typically acute and can affect a high proportion of the population. Among ectothermic vertebrates, affected individuals can present with hemorrhages, edema, and necrosis. Generally, microscopic examination reveals intracytoplasmic inclusion bodies and necrosis of hematopoietic tissues, vascular endothelium, and epithelial cells. Ultimately, the type and severity of the lesions that develop vary depending upon the host species, type of ranavirus, or environmental factors. Our ability to identify lesions caused by ranaviruses is improving because of the knowledge gained from laboratory experiments and the improvement of existing, or development of new diagnostic tests. There is no single Gold Standard test for ranavirus detection, rather the diagnostic test chosen depends on the question asked. For example, a surveillance study may use quantitative real-time PCR (qPCR) to detect ranaviruses, but an investigation of a mortality event may use virus isolation, qPCR, histopathology, electron microscopy, and bioassay. To date, a treatment for ranavirus infections has not been found; however, vaccine development against iridoviruses is showing promise for both DNA and live vaccines within the aquaculture industry.