| Lymphocystis disease (LCD), an important fish disease, is a chronic disease characterized by papilloma-like lesions typically on the skin, fins and tail. These lesions usually regress spontaneously and fish may recover. The causative agent of the lymphocystis disease, lymphocystis disease virus (LCDV), has been identified as a large icosahedral DNA virus and classified in the family Iridoviridae, genus Lymphocystivirus. Although LCDV is not normally a fatal disease, infected fish are more susceptible to infection by other microorganisms, exhibit anaemia, and may have a considerably reduced growth rate. Therefore, the appearance of this viral infection in aquaculture facilities may cause important economic losses. Lymphocystis disease virus has been reported in over one hundred teleost species, including cultured and wild, freshwater, brackish and marine hosts, and it has a world wide geographical distribution. It was first noted in European flounder from British coastal waters, and usually reported in Europe, southern and northern America in the past. But in recent years, more and more reports on LCD appeared in Asia. Japan was the first to find that LCDV can infect flounder Paralichthys Olivaceus. In China LCD has resulted in a great economic loss in marine culture industry and become factors restricting aquaculture development.In this study, the diseased flounder Paralichthys olivaceus with typical lymphocystis symptom were collected from a flounder farm in Weihai, Shandong Province. The LCDV was purified with differential centrifugation followed by sucrose density gradient centrifugation from skin tumours. After centrifugation, two visible bands formed. Observed by electron microscopy after negative staining with 2% phosphotungstic acid, many cell debrises but only a few virions was in band 1, however, large amounts of virus particles were present in band 2 and the virions were... |
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