Lymphocystivirus is a genus of , in the family Iridoviridae.[ Diseases associated with this genus include: tumor-like growths on the skin.]
Hosts
Lymphocystivirus is one of seven genus of within the viral family Iridoviridae, and one of three genera within this family which infect teleostei , along with Megalocytivirus and Ranavirus.[
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Taxonomy
The genus contains the following species, listed by scientific name and followed by the exemplar virus of the species:
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Lymphocystivirus micropogonias1, Lymphocystis disease virus-White croaker (LCDV-WC
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Lymphocystivirus paralichthys1, Lymphocystis disease virus-China (LCDV-C)
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Lymphocystivirus platichthys1, Lymphocystis disease virus 1 (LCDV-1)
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Lymphocystivirus sparus1, Lymphocystis disease virus-Sparus aurata (LCDV-Sa)
LCDV genome
Lymphocystiviruses are Group I viruses with a dsDNA genome. The LCDV-1 genome is approximately 102.7 kilobase pairs (kbp) in length, with 195 potential open reading frames (ORF), and codes for two DNA-dependent RNA polymerase subunits, a DNA methyltransferase, a DNA polymerase, a guanosine triphosphate phosphohydrolase (GTPase), a helicase, , a ribonucleoside diphosphate reductase, and zinc-finger proteins, among others.
Structure
Viruses in the genus Lymphocystivirus are enveloped, with icosahedral and polyhedral geometries, and T=189-217 symmetry. The diameter is around 120-350 nm. Genomes are linear, around 100kb in length.
Life cycle
Lymphocystiviruses attach to the host cell and enter by receptor-mediated endocytosis similar to other iridoviruses.[Eaton HE, Ring BA, Brunetti CR (2010). "The genomic diversity and phylogenetic relationship in the family Iridoviridae." Viruses. 2:1458-1475. http://www.mdpi.com/1999-4915/2/7/1458/pdf] Viral particles are uncoated and move to the cell nucleus of the cell, where DNA replication begins via a virally encoded DNA polymerase.[ The concatameric viral DNA is subsequently packaged via a headful mechanism into virions.][Chinchar VG, Essbauer S, He JG, Hyatt A, Miyazaki T, Seligy V, Williams T (2005). "Family Iridoviridae 145-162. In Fauquet CM, Mayo MA, Maniloff J, Desselburger U, Ball LA (eds). Virus Taxonomy, Eighth report of the International Committee on Taxonomy of Viruses. Academic Press, San Diego, USA.] The lymphocystis viral genome is circularly permuted with terminally redundant DNA.[ DNA-templated transcription is the method of transcription. Fish serve as the natural host.]
Pathogenesis
Lymphocystis disease is a chronic disease that rarely causes mortality.[ Infection causes transformation and hypertrophy (approximately 1000x) of cells in the dermis, forming grossly visible lymphocystis nodules, as well as transformation and hypertrophy in cells of the connective tissues of various internal organs.][ Fibroblasts and osteoblasts are specifically targeted by the virus.][ Lymphocystis viruses are not easily grown in cell culture,][ placing limitations on in vitro molecular pathogenesis experiments.
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Diagnostic pathology
As lymphocystis viruses are not easily grown in cell culture,[ diagnosis is based on clinical signs, gross pathology, histopathology, serology, and/or polymerase chain reaction (PCR)-based molecular .
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Gross pathology
The pathology of lymphocystis consists of papilloma-like skin lesions composed of greatly hypertrophied infected host cells embedded in extracellular matrix, sometimes called lymphocystis tumor cells, which are grossly evident as white spots on the skin and fins of infected fish.
Histopathology
In a recent comparison of lymphocystis histopathology of four unrelated marine species, consistently associated with lymphocystis included hypertrophy cells displaying irregular nuclei, basophilic inclusion bodies that stained positively via Feulgen and Mann's reaction and Periodic acid-Shiff (PAS)-positive hyaline capsules.[ Hyaline capsules arise from the extracellular matrix that is produced by the infected cells,][ and are composed of sulphated and carboxylated glycoproteins (acid mucopolysaccharides).][ In contrast, the inclusion body shape, distribution of viral particles within the cytoplasm and overall appearance of lymphocystis nodules varied by species.][ The species examined in this study included the white-spotted puffer ( Arothron hispidus), the Japanese sea bass ( Lateolabrax japonicus), olive flounder ( Paralichthys olivaceus) and the "sting fish" or Schlegel's black rockfish ( Sebastes schegeli) ][
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Serology
Several serologic assays have been developed to identify LCDV infections, including flow cytometry,[ However, PCR-based molecular assays are more practical for most applications.][
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Electron microscopy
Transmission electron microscopy (TEM) of infected cells reveals cytoplasmic virus particles typically measuring from 198-227 nm in diameter[ (in some cases as large as 380 nm)][
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Molecular pathology
Published PCR primers and protocol are available to amplify a portion of the LCDV-1 MCP.[ When the PCR diagnostic assay is combined with slot blot, diagnostic sensitivity is increased, facilitating the diagnosis of asymptomatic LCDV-1 infections.][
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External links
