Histopathological Study Of Visceral Sarcoidosis In American Shad(Alosa Sapidissima)

In 2018,an agnogenic fish dying incident was emerge in the industrialized fishery of American shad at the Jiading,Shanghai.Disinfectants and antibiotics treatment did not cure effectively.A large number of white nodules were distributed on the surface of organs such as kidneys and other organs.No literature had been reported these clinical symptoms,we tentatively supposed as visceral sarcoidosis of American shad.In this experiment,8 sick shad were used to pathology assay.HE staining,masson staining,Ziehl-Neelsen staining and submicroscopic structure observation were used to analyze the pathological change and the location of the suspected pathogens.The anatomical results showed that there were no obvious symptoms on the surface of the sick shad.However,a large number of 1-2 mm white nodules were distributed on the surface of organs such as liver,spleen and kidney.Liver were deep red along with many ruptures and bleeding;The surface of the kidney was covered with white nodules,and some tissues were eroded and necrotic;the spleen was dark black,and the number of nodules on surface was relatively smaller than that of liver and kidney;Histopathology and ultrastructural observation analysis showed as follow: HE staining showed that the liver,spleen and kidney emerged a large number of granulomas in the microstructure,and distributed largely and much more among the tissues.The Ziehl-Neelsen staining showed that the granuloma center was composed of necrotic tissue fragments and consortia.HE staining showed a large number of infiltration of eosinophils were in the periphery.Masson staining showed that the envelope was composed of fibroblasts and fibroblasts.HE staining showed a large number of vacuoles which were steatosis in the liver,the hepatic cell structure disappeared completely,and a large number of red blood cells and eosinophils were distributed among the tissues.The renal tubules shrank,the lumens ruptured and decomposed in the kidney,and the original structure of kidney was lost.A large area of necrosis and disintegration of the kidney interstitium occurred.The nucleoplasm of epithelial cells dissolved,the nuclear membrane disappeared,and the structure of Golgi and endoplasmic reticulum were unclear;The spleen tissue was filled with a large number of red blood cells,and the spleen tissue cells were covered with a large number of suspicious pathogens with different sections and higher electron density.Ziehl-Neelsen staining and transmission electron microscopy observations of the tissues also confirmed that the granulomatous lesion may be caused by a brevibacterium.Therefore,the fish's autoimmunity continued to phagocytize the bacteria due to the bacteria infected various tissues and organs.Because of the pathogenic bacteria bloom in the tissues,immune cells could not fully phagocytize them,thus there was a large amount of necrosis in the interstitial cells.The granuloma tissue wraped a large number of pathogenic bacteria and necrotic tissues to occupy the original tissue cells.With the increasing of granuloma number and size,the normal physiological function of the liver was blocked,the detoxification ability was reduced,and the immune function of the kidney and spleen was also reduced.Finally,the destroyed immune system could not work normally causing fish dying.