Multiplication of Canine Coronavirus in CRFK Cells

Abstract

Canine coronavirus produced CPE in CRFK cells without any blind passages. Syncytium formation was one of the most prominent cytopathic changes after inoculation at a low multiplicity of infection (MOI) of 1 TCID₅₀/cell. At a high MOI of 50 TCID₅₀/cell, however, rounding and detachment of the cells occurred, but no syncytium formation was found. Specific immunofluorescence and immunoperoxidase staining were confined in the perinuclear cytoplasm at 4 hr postinfection when infective titers of culture fluid began to increase. Virus titers reached their maxima of 10^4.2 and 10^5.3 TCID₅₀/0.1ml after infection at an MOI of 1 and 50 TCID₅₀/cell respectively. Electron microscopic observation revealed that virus particles occurred in the restricted area of the perinuclear cytoplasm, mainly at the Golgi field, in the early stage of infection. Localization of virus particles as well as positive immunofluorescence and immunoperoxidase staining for specific CCV antigen was seen in the same area of infected cells, i.e., around the centriole and Golgi complex and perinuclear cytoplasm in an indentation in the early stage of infection.