Encephalomyocarditis Infection of the Newborn Mouse Myocardium

The myocardium of two- to three-day-old mice killed one day after intraperitoneal infection with encephalomyocarditis (EMC) virus was studied with an electron microscope. Crystalline aggregates of virus particles arranged in a cubic configuration were located within the myocardium of all infected animals; and all infected animals had myocardial lesions. Alterations in myocardial ultrastructure which followed viral infection included margination of nuclear chromatin, loss of granules in areas of nucleoplasm, vesiculation and vacuolation of the sarcoplasm, disruption and dissolution of myofibrils, swelling of mitochondria with separation of mitochondrial cristae, formation of blebs at the periphery of myocytes, dissolution of the sarcolemma and increases in ribosomal granules. We concluded that the cytopathologic effects observed here were due to direct infection of the myocardium by EMC virus.