Studies On Lymphocystis Disease Of Arothron Hispidus Linnaeus

The histopathological and histochemical features of lymphocystis of Arothron hispidus Linnaeus are studied using light and transmission electron microscopy and histochemical methods. The lymphocystis cells are 380-400um in diameter. The nucleus is irregular in shape and the chromatin is marginated. The basophilic, high electron-density inclusion body, positively stained with Feulgen and Mann's reaction, are located at the cell periphery in dot or mass shape. Numerous virus particles are observed within the cytoplasm and around inclusion body, which are hexagonal profiles and about 200nm from side to side with a center core of 135-150nm in diameter. The hyaline capsule enclosing lymphocystis cell is homogeneous and stained PAS-positive showing that it contain acid polysaccharide. All these structures are the typical features of lymphocystis disease of fish. While the sample took in June doesn't contain virus particles, breakdown of connective cells and cell debris are observed, suggesting that the diseased fish is recovering due to medication.A nested polymerase chain reaction (PCR) is developed for detection of lymphocystis disease virus. The nested PCR is based on the sequences of gene from major capsid protein (MCP). Two sets of primers are designed, primers set, P1:P2, is for the first step of amplification and yield a product of around 348bp, the second primer, P3:P4, is designed to yield a product of around 172bp from the fragment amplified by the first primer set. The sensitivity of this two-step amplification was 107 times higher than that of the one-step amplification by primer set (P1:P2). Using nested polymerase chain reaction, samples from Arothron hispidus, took in April and June, yield an amplification product showing the sample in April contains lymohcystis disease virus but the sample in June doesn't.Indirect immunofluorescence assay test is done for the detection of lymphocystis viral antigens using monoclonal antibody against lymphocystis disease virus (LCDV) from flounder Paralichthys olivaceus as the first antibody and IgG-FLTC as the second body0 Green fluorescence is observed in the cytoplasm of lymphocystis cells, while the nucleus and connective tissue is negative-stained. On the other hand, immunogold-silver technique using monoclonal antibody against flounder lymphocystis disease virus shows that the cytoplasm of lymphocystis cells is positive-stained (black in color). All these results reveal that the LCDV exist in the cytoplasm of lymphocystis cells.Test shows that antibiotics, such as terramycin and chloromycetin, as well as antitoxin and Formalin have no obvious effect to cure lymphocystis disease. But the lymphocystis nodules can become smaller by rearing the fish in the seawater of 24 ~ 25 C in combination with H2O2 (50ml/m3).