Pathogenicity of an attenuated, temperature-sensitive mutant of western equine encephalitis virus induced by a chemical mutagen

Comparative neurovirulence of selected vesicular stomatitis virus temperature-sensitive mutants of complementation groups II and III

Weanling mice were inoculated intracerebrally with selected vesicular stomatitis virus (VSV) complementation group II and III temperature-sensitive (ts) mutants. Of the VSV ts mutants studied, only ts G32, a group III complementation mutant, appeared neurovirulent. Interestingly, neither the capacity to replicate in central nervous system tissue nor the ability to replicate in certain neurally derived continuous cell lines at semipermissive or nonpermissive temperatures appeared different among the VSV ts mutants employed. Finally, the pathological alterations in central nervous system tissue produced by VSV ts G32 were entirely different than those produced by G31 VSV ts in the group III mutant. These studies support the hypothesis that both the virological and neuropathological features produced by different VSV ts mutants are dependent upon the unique characteristics of each mutant, rather than upon a common biochemical defect shared by all members of a complementation group.

A hamster-attenuated, temperature-sensitive mutant of Venezuelan encephalitis virus

Pathogenicities of 10 temperature-sensitive mutants of Venezuelan encephalitis virus were studied using the hamster model of human virulence. The parental strain and nine of the temperature-sensitive mutants produced lethal infections in hamsters. Strain ts 126 showed reduced hamster virulence. Deaths with the lethal mutants usually occurred 1 to 3 days later than with parental virus. Nine mutants produced lower levels of viremia than parental virus. Attenuation of ts 126 was related to restriction of viral growth in spleen and probably bone marrow and to absence of the usual pathological lesions in hemopoietic tissues and brain, but was functionally unrelated to temperature sensitivity since temperatures of both normal and infected hamsters remained within the permissive range of the mutant. Deaths did not correlate with titers of the 10 mutants in blood at permissive temperatures or with reversions of four temperature-sensitive mutants to non-temperature-sensitive virus in hamsters.

A spontaneous temperature sensitive mutant of Japanese encephalitis virus: preliminary characterization

A spontaneously arising temperature sensitive (ts) mutant of Japanese encephalitis virus (JEV), ts104, was isolated from chick fibroblast (CF) cell cultures of JEV strain M 1/311. Strain ts104 was plaque purified and characterized to ascertain its potential as a candidate for a live vaccine. Parameters of its growth, temperature lability, immunogenicity and virulence were examined. Ts104 has been shown to be stable ts JEV strain, multiplying as well as the parent strain in CF cultures at 35 degrees C, but not mutiplying at 39 degrees C. It was avirulent for embryonated chicken eggs incubated at 39 degrees C and of reduced virulence for intracerebrally (i.c.) inoculated mice as measured by LD50 in weanling mice and average day of death in weanling and suckling mice. Intraperitoneal injection of adult mice with either parent or ts strain resulted in similar levels of protection against challenge with either strain. The potential of ts104 as a candidate live JEV vaccine strain is discussed.