Evaluation of ultrastructural changes associated with encephalomyocarditisvirus in the myocardium of experimentally infected piglets

Objective-To evaluate the ultrastructural changes and localization of encep halomyocarditis virus (EMCV) and viral pathogenesis in the myocardium of ex perimentally infected piglets. Animals-Eight 20-day-old piglets, Procedure-Six piglets were inoculated oronasally with 5 ml (10(6) median ti ssue culture infective dose/ml) of EMCV suspension, and 2 were used as unin fected controls, Piglets were euthanatized or died between postinoculation days 1 and 3. Samples of heart tissue from all piglets were evaluated histo logically, by virus isolation, and by use of immunohistochemistry and elect ron microscopy. Results-All Infected piglets had gross or microscopic lesions of interstiti al myocarditis. immunohistochemically, EMCV antigen was detected in the cyt oplasm of cardiac muscle cells, Purkinje fibers, and endothelial cells and in the nucleus of cardiac muscle cells and Purkinje fibers. Ultrastructural lesions were characterized by degeneration and necrosis of cardiac muscle cells and Purkinje fibers. Virus was present intracytoplasmically In cardia c muscle cells, Purkinje fibers, and endothelial cells of capillaries and i ntranuclearly in cardiac muscle cells. The cell membranes of the Purkinje f ibers and endothelial cells had distinct protrusions that contained virus p articles. In control piglets, no lesions were found, and no EMCV antigen wa s detected. Conclusions-Localization of EMCV intracytoplasmically or intranuclearly In various myocardial cells may well reflect the sites of viral proliferation. The presence of virus particles In cell membrane protrusions and in vacuol es within the lumen of capillaries indicates that virus is released not onl y by disintegration of the host cell but also via exocytosis.