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The structure and topography of the Bursa of Fabricius (BF) differs from other central immune organs. Structural components, providing BF function are located in mucosa, which is constantly influenced by antigen stimulation. Therefore the reports, which have appeared recently, indicate that BF may function as a peripheral immune organ. The latter is known to be situated in the alimentary canal mucosa (caecal tonsils, Peyer's patches) and possess peculiar epithelium. The aim of our study was to investigate the structure and cell composition of BF epithelium in chicken, turkey, quails, ducks and pigeons using light and electronic microscopy. The studies have shown that epithelium overlying BF folds is pseudostratified columnar, but between them and in their base it might be cuboidal or columnar. Pseudostratified epithelium consists of columnar cells with a few microvilli on their apical surface, goblet cells, infrequent endocrine cells and macrophages. BF epithelium is spongious due to its infiltration by lymphoid cells. The large quantity of the latter is found in subepithelial connective tissue. Infiltration by lymphoid cells is considered to be typical for the alimentary tract mucosa, where the aggregated lymphoid nodules are situated. Thus, our study supports the thoughts that BF may have function of central and peripheral immune organ.

In recent years, there is a tendency to increase the incidence of the disease in dogs with signs of diarrhea, not only in Ukraine but also in Europe.The ar cle presents the results of a study on histological changes in organs and ssues of dogs with coronavirus infec on. A histological study of pathological material sampled from 6 dogs of various breeds and gender, aged from 2 to 6 months, died from diarrheal syndrome was carried out. The presence of the coronavirus was confirmed in fecal samples by a polymerase chain reac on.The most expressed injuries and typical changes in all dead dogs we recorded in the small intes ne, namely in the jejunum and ileum, regional lymph nodes, and also the spleen.Morphological manifesta ons of coronavirus infec on in dogs at the macroscopic level are the following signs: the presence of exuda ve inflamma on in the small intes ne in form of serofibrinous jejunoilei s, hyperplasia and serohemorrhagic lymphadeni s of the mesenteric lymph nodes, mul ple foci of hemorrhage in the parenchyma of the spleen and serous membrane of the small intes ne, passive venous hyperemia of the liver and kidneys, dilata on of the right ventricle of the heart, pulmonary edema, cachexia and dehydra on of the body.At the microscopic level, we registered the following: serofibrinous jejunoilei s, hyperplasia of the lymphoid nodules of the spleen and lymph nodes, hemorrhagic infarc ons in the spleen, hyperplasia of individual and aggregated lymphoid nodules in the small intes nal mucosa, degenera ve processes in the parenchyma of the liver and kidneys.

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A pathological autopsy was performed on 6 corpses of piglets in the first week of life who died from mycoplasmosis. Examination of the visible mucous membranes revealed hyperemia of the mucous membrane of the nasal cavity and thymus. Simultaneous lesions of the pharyngeal, parotid, cervical, mandibular lymph nodes were noted. They were slightly enlarged, from dark pink to dark red. The heart is irregularly shaped due to the expansion of the right ventricle or the diffuse expansion of all departments. Lungs have doughy consistency, uneven color. In some cases, there are diffuse red areas covering the entire lobe of the lungs, in other cases, there is a defeat of small areas. The liver has a smooth surface, soft or pasty consistency, the parenchyma pattern is slightly smoothed in section. The color of the liver is different: dark red areas, without clear boundaries turn into creamy-clay. Flatulence was a characteristic feature of the stomach and intestines. Catarrhal enteritis was registered in animals, which manifested itself in the form of moderate hyperemia of the intestinal mucosa and serous membranes. Microscopically, there is a significant blood supply to the vessels in the lungs. Alveoli are half fall down, in the form of slit-like lumens. In areas of tissue infiltration by inflammatory infiltrate, the alveolar wall is thickened, alveocytes are in a state of turbid swelling and vacuolar dystrophy, they are impregnated with erythrocytes. Peribronchial pneumonia of lymphocytic character is observed. The liver is in a state of acute venous hyperemia. The central and intraparticle capillaries are sharply dilated and filled with blood in some lobes, and the hepatic beams are compressed accordingly. In the center of other lobes, diffuse infiltration of liver tissue by erythrocytes as a consequence of diapedesis is noted. Hepatocytes are in a state of granular dystrophy. Destructive changes are strongly expressed in the mucous membrane of the small intestine: desquamation of the epithelium, necrosis of epitheliocytes and villi, destruction of crypts. In the brain tissue, there is dilation of the lumens of large and small blood vessels, extracellular and perivascular edema, areas of reactive necrosis.