Lymphocystis

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Lymphocystis Disease

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History First described viral disease of fish (Lowe, 1874) reported in European flounder. Proof of viral etiology came by EM studies (Walker, 1962) and virus isolation in BF-2 cells (Wolf et al. 1966) Lymphocystis is a common, chronic and benign infection caused by an iridovirus that results in uniquely hypertrophied cells, typically in the skin and fins of only the more advanced orders of fishes.

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Host and geographic range Occurs in freshwater and marine species. Global distribution – Europe, British Isles, North America, Australia, Africa, Central Amercia, Japan. Susceptible species include herrings, smelts, batfishes, killifishes, scorpion fishes, basses, sea basses, sunfishes, perches, snappers, drums, goatfishes, scats, butterfly fishes, cichlids, damselfishes, wrasses, gobies, rabbitfishes, flounders, porcupine fishes, etc. Occurrence of lymphocystis in Asia: Reported among ornamental fish (Scatophagus argus), pond-cage cultured seabass (Lates calcalifer), grouper fingerling in Thailand; wild snakehead in the Philippines, flounder in China.

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Epidemiology LCD is characterized by the external appearance of nodules, either singly or in groups, on skin, fins, or tail of the affected fish. Although, LCD is not a fatal disease, the external appearance might cause a significant economic loss. The principle mode of transmission of LCD is horizontally via direct contact and external trauma. Other factors such as water contamination and stress condition caused by high population density, nutrition deficiencies, decreased dissolved oxygen, suboptimal water quality, or human manipulation may increase the appearance of LCD symptoms. Recent study reported that Artemia sp. might act as a reservoir host of this disease (Cano et al., 2009).

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Causative agent Species: 00.036.0.04.001.Lymphocystis disease virus-1 Genus: 00.036.0.04. Lymphocystivirus Family:00.036. Iridoviridae LCDV is an icosahedral symmetry virus, approximately 200-300 nm in diameter, and contains single linear double stranded DNA Double stranded DNA is circularly permuted. The genome has terminally redundant sequences. The genome has high level of methylation of cytosine residues.

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Virions consist of an envelope, a capsid, and an internal lipid membrane. Surface projections are distinctive protrusions surrounded by a prominent fringe. Surface projections are 2.5 nm long. Capsid/nucleocapsid is round and exhibits icosahedral symmetry. The isometric capsid has a diameter of 190-220 nm. The capsid shells of virions are composed of two layers (of unit membranes). Capsids appear hexagonal in outline. Lipids are present and located in the internal component. Virions are composed of 3-14% lipids by weight. The composition of viral lipids and host cell membranes are distinctly different. The lipids are not derived from host membranes.

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Signs and pathologic changes Lymphocystis is a terminal infection of individual cells, and the effect on the host is generally slight. The virus is typically dermatotropic and superficial; the condition is much like that of warts, in that the lesions are macroscopic and occur mostly at the periphery of the vascular system.

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Diagnosis Behaviour Infected fish behave normally but extensive growths can slightly affect swimming. Among fish in confinement, and conceivably in the wild, the protruding clusters of cells lead to aggression and cannibalization of the lesions. External signs Cauliflower-like lesions on body surface, including mouth region, fin and tail region Laboratory diagnosis PCR In-situ Hybridization

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Control/Treatment: No known method of therapy or immunization. Avoidance – is the universal control measure; infected fish should be removed from population; improve water quality; stocking density should be decreased because transmission is through direct contact.

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Hypertrophied cells, called lymphocystis cells (LC) Magnification of lymphocystis cell (LC)

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