Abstract
The histo-and cyto-pathological changes in the exocrine portions of the pancreas and in the liver were observed in the fingerling of the infected rainbow trout (Salmo gairdneri Richardson).Symptoms of the trouts suffered from infectious pancreatic necrosis (IPN) disease are the dark coloration, exophthalmos, and acites.
Although the extent of the necrotic or degenerated lesions in the cytoplasm ot the pancreatic acinar cells was different from cell to cell, a number of cells displayed one, several, or all of the following structures in the cytoplasm: myelin-figured lysosomes with often intermingled virions;necrotic degeneration of zymogen granules;and of flattened layered cisternae of rough endoplasmic reticulum accompanied with loss of ribosomes;grouped virions;cytolysomes containing several of the myelin-figured electron dense material, virions, cell organelles, fine filaments, winding membranous structures;and clear zymogen granules containing a flocculent material.In more advanced and the most advanced cases there appeared pycnotic nuclei of the acinar cells, cellular detritus, degen-erated cell organelles such as mitochondria which are often scattered in the intercellular space, and in the exocrine portions there appeared some regions electron-microscopically indistinguishable from each other by fusion of several acinar cells.Also in the hepatocytes pathologically displayed cytoplasmic structures were almost similar to those of the acinar cells except degeneration of zymogen granules.However, the extent of necrotic lesions.of the hepatic tissue was so far small as compared with the pancreatic tissue in one and the same individual, and a heavy destruction of the acinar cells in several regions of the pancreatic tissue was accompanied with the beginning of the necrotic degeneration of hepatocytes with accumulations of fat droplets different in size and increase of lysosomes.In the pancreatic and hepatic tissues of IPN disease infiltration of macrophages and two or polymorphonuclear wandering cells was conspicuous, and these cells and Kupffer's stellate cells contained a large number of lysosomes and one to three cytolysomes.
The majority of virions in the pancreatic acinar cells, hepatocytes, wandering cells and Kupiffer's stellate cells appeared in lysosomes and cytolysomes identified with the intracytoplasmic inclusions by light microscopy, in which virions became indistinct in profile and were destroyed to transform electron dense myelin-figured and finely granular materials.A round, oval, or bacilliform materials occupied by an electron dense myelin figure alone were often discharged into the intercellular space.
In ultra-thin sections, virions (size range of 50-60 mμ, an average diameter of 54.3mμ) appeared unenveloped, and hexagonal to round in appearance.The virus perhaps is IPN virus and may belong morphologically to reovirus group in comparison with the observa-tions by Moss and Gravell (1969).
Near the virions of various numbers, two kinds of rod-like bodies having an average diameter of 60 mμ and 28 mμ often appeared setting in parallel array or crossing in irregularity, respectively.The end of the rod-like bodies often showed roundness, and the transverse sections of them showed a round shape and tubular structures exhibiting a clear central portion.
