Experimental study of tropism in cultivated canine coronavirus in the small intestine of puppies

Abstract

The varying extents of natural disease induced by coronavirus in dogs are not completely clear because the pathogenesis of coronavirus enteritis is not studied sufficiently. In this study, based on the results of clinical, virological, morphological and histochemical studies, we determined the pathogenic role of coronavirus in infected dogs using experimental infection, per os, of isolated canine coronavirus (Nick) with titer of infectious activity equaling 4.8 ± 0.04 lg TCID50/cm, cultivated on heterologous cell cultures. This allowed us to determine, supplement, and generalize the data on pathogenesis of the disease and determine the histological changes in the small intestine, where the initial replication of the pathogen takes place. It was found that lesions and the pattern of the pathomorphological changes (destruction, necrosis and edema of the stroma of the villi, lysis of the cytoplasm, deformation of the enterocyte nuclei) in the small intestine of experimentally infected dogs depend on the development of the pathological process related not only to the changes in histoarchitectonics of the wall of the intestine, but also to tension of the histochemical statics, and obviously the dynamic of the cells (accumulation of the main and acidic proteins in enterocytes’ cytoplasm, hypersecretion of the mucus by goblet cells, decrease of Schiff iodine acid-positive substances in the enterocytes’ cytoplasm, formation of basophilous inclusion bodies), which leads to disorders in metabolic processes in the organism of infected dogs as a response to the virus infection. The examined dogs were found to have morphological changes in the small intestine similar to those in spontaneously infected animals. During the action of coronavirus, the contacts between the enterocytes become damaged, which leads to inhibition of the protective functions of the intestine. At the same time, the pathological process in the experimentally infected animals developed rapidly and had an acute course. Thus, coronavirus enteritis as a separate disease is practically unobserved in field conditions, which makes microscopic survey of the pathogenic impact of the latter on the organism of dogs impossible. Therefore, experimental mono-infection allows a detailed study to be conducted of pathomorphological changes of the initial place of the reproduction of the virus – the small intestine affected by coronavirus enteritis.