Arginine metabolism in infected cell cultures as a marker character for the differentiation of orthopoxviruses.

Arginine has been shown to be essential for the replication of several orthopoxviruses in mouse sarcoma 180 cells and in chick embryo fibroblast cultures. Both host systems are characterized by their inabilities to utilize citrulline for the biosynthesis of arginine due to deficiencies in the requisite cellular enzymes and cell multiplication is absolutely dependent on the availability of exogenous arginine. Virus replication in such cells maintained with citrulline results from the induction of virus-specific enzymes. Significant virus yields in the absence of exogenous arginine or citrulline can arise from the replenishment of intracellular amino acid pools by increased utilization of arginyl residues in cellular proteins. The extent of the phenotypic expression of these characters in infected cells permitted significant discrimination between the viruses examined. Distinctions could be drawn between rabbitpox, ectromelia, cowpox, buffalopox and vaccinia strains. However, cowpox could not be distinguished from other viruses isolated from diseased animals in European zoos.