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.