Cytopathic and immunogenic studies of sheep pox virus serially cultivated in cell culture

Abstract

Lamb kidney (LK) and lamb testis (LT) cell cultures of serially passaged sheep pox virus (SPV) were examined for their cytopathogenicity and immunogenicity. All 3 SPV strains used behaved similarly in both traits. While the CPE was examined at low (4th), mid (18th) and high (40th) passages, the low and mid-passaged LT virus produced cytological changes almost identical to those of the LK virus. With acridine orange staining the cytoplasmic inclusions, seen in infected cells stained by May-Grunwald-Giemsa or HE, gave a greenish-yellow fluorescence suggestive of viral DNA and intracytoplasmic replication. In contrast, the high-passaged LT virus induced unusual intranuclear inclusions without any change in the cytoplasm. With acridine orange these inclusions exhibited a greenish-yellow fluorescence indicative of viral DNA and intranuclear replication. In tests on the immunity conferred by high LK cell culture passaged virus, immunized sheep resisted challenge, whereas sheep given high-LT cell culture passaged virus developed a generalized infection after challenge. It is concluded that the virus used for immunization should possess the property of intracytoplasmic replication.