Characteristics of a Coronavirus (Strain 67N) of Pigs

Abstract

SUMMARY A virus (strain 67N) isolated from the nasal cavity of apparently healthy swine was classified morphologically as a coronavirus. By negative staining, virions of strain 67N appeared approximately circular in outline and were covered with club-shaped projections. Their mean diameter of 120 nm. correlated with size estimated by filtration. Of this dimension, the diameter of the membrane-bound portion of the virion was 90 nm. and the projections were approximately 15 nm. long. In thin sections of infected embryonic porcine kidney ( epk ) cells, viral particles were seen intracytoplasmically, mainly within vesicles and extra-cellularly along plasma membranes. Virus-induced changes in plasma membranes of epk cells were indicated by hemadsorption and by formation of syncytia; however, the membranes appeared structurally unaltered. Examination of infected epk cells with immunofluorescence microscopy revealed viral antigen only in the cytoplasm. Fluorescence was often more intense in the central portion of syncytia. In mononucleated cells, intense focus of fluorescence was frequently in a juxtanuclear position. Both virus-induced hemagglutination and hemadsorption occurred with erythrocytes of mice, hamsters, rats, chickens, and turkeys, but not with erythrocytes of guinea pigs, calves, sheep, pigs, geese, horses, rabbits, and man.