Fish Rhabdovirus Replication in Non-Piscine Cell Culture: New System for the Study of Rhabdovirus-Cell Interaction in Which the Virus and Cell Have Different Temperature Optima

Abstract

The replication of three rhabdoviruses associated with diseases of fish has been demonstrated in cells of continuously cultivated non-piscine cell lines. Spring viremia of carp (SVC) virus and the salmonid fish viruses, Egtved and infectious hematopoietic necrosis virus, all replicated in mammalian WI-38 (human diploid cell strain) and BHK/21 cells and in cells of one or more reptilian cell lines at the temperatures commonly used to propagate these viruses in fish cells. The infections were cytopathic: SVC virus plaque assays may be performed in several types of mammalian cell culture. “Autointerference” apparently mediated by abortive “T” particle formation was observed during serial nondiluted passages of SVC virus in BHK/21 and TH1 cells, but not in RTG-2 or WI-38 cells. Optimal temperatures for replication of SVC and Egtved viruses in BHK/21 cells were identical to those determined in poikilothermic vertebrate cell cultures. However, these viruses replicated relatively more efficiently at suboptimal temperatures in “cold-blooded” vertebrate cells than in the hamster cells. Studies of [ 3 H]uridine incorporation into uninfected BHK/21 cells incubated at different temperatures revealed that [ 3 H]uridine uptake is sharply reduced at temperatures below 24.5 C. Growth curve studies of SVC virus in BHK/21 cells incubated at 23 C revealed that a clear-cut large excess of virus-induced [ 3 H]uridine incorporation could be demonstrated in the absence of actinomycin D. Actinomycin D treatment (1 μg/ml) led to efficient inhibition of control cell [ 3 H]uridine uptake, but also markedly reduced the total counts per minute of virus-induced [ 3 H]uridine uptake, without depressing the yield of released infectious virus. Actinomycin D added to SVC virus-infected BHK/21 cell cultures at concentrations as low as 0.01 μg/ml caused a significant decrease in the level of virus-induced [ 3 H]uridine uptake, despite the fact that this concentration is insufficient to efficiently suppress “background” cellular [ 3 H]uridine incorporation.