Lymphocystivirus

Lymphocystivirus is one of seven genera of viruses within the viral family Iridoviridae, and one of three genera within this family which infect teleost fishes, along with Megalocytivirus and Ranavirus. Lymphocystiviruses infect more than 140 freshwater and marine species, spanning at least 42 host families worldwide, causing the chronic, self-limiting clinical disease, lymphocystis. While lymphocystis does not cause mass mortality events like megalocytiviruses and ranaviruses, fish with lymphocystis exhibit grossly visible papilloma-like skin lesions which substantially reduce their commercial value. No vaccines are currently available for lymphocystis viruses. ==Taxonomy==

The genus contains the following species, listed by scientific name and followed by the exemplar virus of the species: • Lymphocystivirus micropogonias1, Lymphocystis disease virus-White croaker (LCDV-WC • Lymphocystivirus paralichthys1, Lymphocystis disease virus-China (LCDV-C) • Lymphocystivirus platichthys1, Lymphocystis disease virus 1 (LCDV-1) • 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, protein kinases, a ribonucleoside diphosphate reductase, and zinc-finger proteins, among others. The LCDV-2 genome is similar to that of LCDV-1 but is slightly smaller, approximately 98 kilobase pairs (kbp) in length. ==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. Viral particles are uncoated and move to the nucleus of the cell, where DNA replication begins via a virally encoded DNA polymerase. Viral DNA then moves to the cytoplasm for the second stage of DNA replication, which results in the formation of DNA concatemers. 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. ==Diagnostic pathology==

As lymphocystis viruses are not easily grown in cell culture, These lesions proliferate as epithelial tumors in some cases. Histopathology In a recent comparison of lymphocystis histopathology of four unrelated marine species, lesions consistently associated with lymphocystis included hypertrophied cells displaying irregular nuclei, basophilic cytoplasmic inclusion bodies that stained positively via Feulgen and Mann's reaction and Periodic acid-Shiff (PAS)-positive hyaline capsules. immunoblot, and immunofluorescence. and electron-dense substances in the perinuclear space. 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. == References ==