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Diseases of Aquatic Organisms

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DAO 130:11-24 (2018)  -  DOI: https://doi.org/10.3354/dao03250

Phylogenomic characterization of two novel members of the genus Megalocytivirus from archived ornamental fish samples

Samantha A. Koda1, Kuttichantran Subramaniam1, Ruth Francis-Floyd2, Roy P. Yanong3, Salvatore Frasca Jr.4,8, Joseph M. Groff5, Vsevolod L. Popov6, William A. Fraser7, Annie Yan7, Shipra Mohan7, Thomas B. Waltzek1,*

1Department of Infectious Diseases and Immunology, College of Veterinary Medicine, University of Florida, Gainesville, Florida 32611, USA
2Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, Florida 32608, USA
3University of Florida School of Forest Resources and Conservation, Program in Fisheries and Aquatic Sciences Tropical Aquaculture Laboratory, Ruskin, Florida 33570, USA
4Conneticut Veterinary Medical Diagnostic Laboratory, Department of Pathobiology and Veterinary Science, University of Connecticut, Storrs, Connecticut 06269, USA
5Fish Health Laboratory, School of Veterinary Medicine, University of California, Davis, California 95616, USA
6Department of Pathology, University of Texas Medical Branch, Galveston, Texas 77555, USA
7Florida Department of Agriculture and Consumer Services, Bronson Animal Disease Diagnostic Laboratory, Kissimmee, Florida 34741, USA
8Present address: Department of Comparative, Diagnostic, and Population Medicine, College of Veterinary Medicine, University of Florida, Gainesville, Florida 32610, USA
*Corresponding author:

ABSTRACT: The genus Megalocytivirus is the most recently described member of the family Iridoviridae; as such, little is known about the genetic diversity of this genus of globally emerging viral fish pathogens. We sequenced the genomes of 2 megalocytiviruses (MCVs) isolated from epizootics involving South American cichlids (oscar Astronotus ocellatus and keyhole cichlid Cleithracara maronii) and three spot gourami Trichopodus trichopterus sourced through the ornamental fish trade during the early 1990s. Phylogenomic analyses revealed the South American cichlid iridovirus (SACIV) and three spot gourami iridovirus (TSGIV) possess 116 open reading frames each, and form a novel clade within the turbot reddish body iridovirus genotype (TRBIV Clade 2). Both genomes displayed a unique truncated paralog of the major capsid protein gene located immediately upstream of the full-length parent gene. Histopathological examination of archived oscar tissue sections that were PCR-positive for SACIV revealed numerous cytomegalic cells characterized by basophilic intracytoplasmic inclusions within various organs, particularly the anterior kidney, spleen, intestinal lamina propria and submucosa. TSGIV-infected grunt fin (GF) cells grown in vitro displayed cytopathic effects (e.g. cytomegaly, rounding, and refractility) as early as 96 h post-infection. Ultrastructural examination of infected GF cells revealed unenveloped viral particles possessing hexagonal nucleocapsids (120 to 144 nm in diameter) and electron-dense cores within the cytoplasm, consistent with the ultrastructural morphology of a MCV. Sequencing of SACIV and TSGIV provides the first complete TRBIV Clade 2 genome sequences and expands the known host and geographic range of the TRBIV genotype to include freshwater ornamental fishes traded in North America.


KEY WORDS: Iridoviridae · Megalocytivirus · Infectious spleen and kidney necrosis virus · Red seabream iridovirus · Turbot reddish body iridovirus · Phylogenomics · Genome · Keyhole cichlid · Oscar · Three spot gourami


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Cite this article as: Koda SA, Subramaniam K, Francis-Floyd R, Yanong RP and others (2018) Phylogenomic characterization of two novel members of the genus Megalocytivirus from archived ornamental fish samples. Dis Aquat Org 130:11-24. https://doi.org/10.3354/dao03250

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