Cell Culture-Adapted SH Strain of Transmissible Gastroenteritis Virus of Pigs: in Vivo and in Vitro Studies

SUMMARY Effects of Shizuoka (sh) strain of transmissible gastroenteritis (tge) virus at the 35th to the 37th cell culture passage levels were determined in young pigs and primary pig kidney (ppk) cells. In young pigs, the disease produced by the sh strain of tge virus was similar clinically and pathologically to that produced by the prototype Purdue strain. As with the Purdue strain, viral antigens were detected only in the cytoplasm of the columnar epithelial cells of the small intestine with anti-Purdue strain fluorescent antibody. Differences included longer incubation periods, lower mortality, and less extensive villous atrophy in the small intestine. On serial passage in pigs, the sh virus seemed to increase in virulence for pigs, as indicated by shorter incubation periods and production of villous atrophy involving more of the small intestine. Cytopathologic features and growth of the sh strain were examined in ppk cell cultures. The virus entered into an eclipse phase lasting approximately 6 hours. Examination by immunofluorescence indicated that viral antigens appeared in the cytoplasm at the 6th hour postinoculation, and viral maturation and release from cells occurred rapidly. In inoculated cells which were stained with acridine orange, ribonucleic acid (rna) material was seen to increase in the cytoplasm of cells during the later stages of infection. Cytopathic effects (cpe) consisted of rounding of ppk cells and subsequent detachment of the cells from the glass. The virus was inactivated by ethyl ether. Viral replication was not inhibited by the deoxyribonucleic acid (dna) inhibitor 5-iododeoxyuridine (idu), indicating that the virus contained rna. Antigenic relationship between the sh and Purdue strains was demonstrated by neutralization tests, using both cell cultures and pigs as indicators of infection.