Histopathological studies on rickettsia-like organism infection in a cultured fish, Ophiocephalus argus

The histopathological changes of various organs (brain eve, gill, heart, head kidney, liver, hepato-panereas spleen, kidney, intestine and ovary) in rickettsia-like organisms (RLOs) infected fish, Ophiocephalus argus C. have been reported, and the pathological mechanism has been discussed in this paper. The gross pathological characteristics were that cream-coloured nodules, a chronic granun n lonlatou-s ufflainination under nricroscopy, were observed on internal organs of' infected fish,which had diagnostic significance. Because of extensive tissue necrosis and marked fibroblast proliferation,5-10 giant sarcoma-like bodies with a distinctive boundary were seen oil the surface of severe infected kidney. The blood vessels of internal organs showed fibrin thron-lbi,rnixed thrombi and disseminated intravascular coa,,Ldation (DIC), air(] larger areas of tissue and cells showed severe degeneration, necrosis and extensive lysis. Eosinoplrilic intracytoplasmic inclusion- laden cells1which were mainly epithelial cells and phagocytic cells,situated mostly in the epitbeliLlul Of lill,the enclothelimn of blood vessels and the connective tissue near to the blood vessels of gill and internal organs. The intracytoplasmic inclusions could result in swelling and rupturing of endoLhelial cells of blood vessels. The histopathological changes of various organs observed in experimentally infected fish with abundant RLOs were similar to those in naturally infected fish. 'flie marked necrosis and larger granulomas were found in brain tissue,fibrin thrombi were also observed in blood vessels of brain mentbrane. The central necrotic area of granulomas in eye was larger. The gill larnellae were swollen and ruptured, epithelial cells showed necrosis and Sloughed. 'flie myocarditis and pericarditis were seen in hear[. The severe changes were. noted in the kidney. The kidney changes were characterized by the replacement of normal haernatopoieLic tissue with a large number of granulomas in different size. The renal tubules showed videspreacl degeneration. 'fhe renal corpuscles swelled,the glomedus congested. The cavities ofrenal capsule were enlarged in which there were a large number of sloughing epithelial cells. The periphery tissue of kidney showed marked necrosi-s and extensive lysis. 'niough the pathological changes in the head kidney were light to those of the kidnev,marked granulomas N ere -seen. The granulomas in liver were mainly situated at the periphery of organ and the pathological lesion was maird fatty degeneration. `Fhe epithelial cells in hepato-pancreas were swollen the acinar cavities of pancreas disappeared. Spleen lesions were similar to those of the kidney. The intestine mucosa thickened, larger granulomas were observed in tunica muscularis with a distinctive boundary and thinner fibrosa. 'flie eonnective tissue in ovary proliferated, and marked grarmlornas were also seen in ovar