Replication of Theiler's murine encephalomyelitis viruses in BHK21 cells: An electron microscopic study

Abstract

The replication of two different Theiler's murine encephalomyelitis viruses (GDVII and DA) in BHK21 cells was studied by electron microscopy. During the early stages of infection, the changes observed in infected cells were identical for both viruses, and typical of those described in the literature for other picornaviruses. However, fundamental differences in the intracellular development of GDVII and DA viruses were observed late in the infection. Well-developed crystalline arrays of virions were observed in the cytoplasm of GDVII virus-infected cells, and virus was readily released upon cell lysis. In contrast, DA virus did not form similar crystals. Instead, in DA virus-infected cells unique membranous structures consisting of two membrane units enclosing a layer of virions one particle deep were regularly observed in the cytoplasm at late times in the infection. In addition, DA virus did not appear to be freely released upon cell lysis. Single cell growth kinetics of GDVII and DA viruses in BHK21 cells showed a close correlation with the electron microscopic observations. While GDVII virus was released from cells DA virus remained cell associated. The proliferation of similar membranous structures in parallel with maturation of virus particles has not been described previously in electron microscopic studies of other picornaviruses.