| Summary: | Тhe key direction of scientific research is considered to be the study of the characteristics of the course and manifestation of the disease, as well as the determination of virulent properties of pathogens. Calves infected with the agent of viral diarrhea were chosen as a model for study of the infectious process. The study summarizes the pathogenetic mechanisms of development and expression of viral diarrhea. Clinical, biochemical, and immunehematologic features of the disease were specified. data on morphological changes in parenchymal organs of diseased animals were found. Changes in protein, lipid, mineral metabolism, and electrolyte balance indices associated with increased activity of lactate dehydrogenase are considered to be metabolic features of VD. Immunologic research showed a shift in the process of lymphocyte differentiation with activation of the b-cell link of immunity and a decline in the phagocytic index. Calves infected with VD revealed signs of structural immunodeficiency, which is morphologically confirmed by the decrease of most of the lymphoid follicles of the spleen. The lungs displayed signs of catarrhal and purulent bronchitis, manifested by hyperplasia of the bronchial epithelium, desquamation of the epithelium and accumulation of exudate in the bronchial lumen and peribronchial edema. Evidence of serous lymphadenitis were registered in the lymph nodes associated with reduction of subcapsular lymphoid follicles, both in the subcapsular and central sinuses. They were accompanied by the growth of connective tissue in the stroma of the organ.
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