GROWTH OF VEE AND EEE VIRUSES IN CHICK FIBROBLAST CULTURES AT HIGH TEMPERATURES

Abstract

Abstract : The work reported here concerns the study of growth characteristics of Venezuelan encephalitis (VEE) and eastern equine encephalitis (EEE) viruses propagated in CF cells at high temperatures. VEE virus was able to form plaques at 44 C; EEE virus formed plaques to 46 C. Uninfected CF monolayers could tolerate a maximum temperature of 46 C, but were killed at about 47 C. Maximal growth rates and virus yields in liquid overlay cultures were observed to 40 C for VEE virus. Marked inhibition of this virus occurred at temperatures greater than 40 C. No increase in virus titer could be detected at 44 C; at 46 C or greater virus titers dropped rapidly. The growth response of EEE was maximal to 44 C and substantial viral growth took place at 47 C. Further studies indicated that if CF monolayers infected with VEE virus were transferred from 37 C to 44 C at different stages during the viral growth cycle, virus replication was halted almost immediately. In another experiment in which virus-infected monolayers were transferred from 44 C after various periods of time to 37 C, virus replication was initiated within four hours after transfer. These data indicate that the differences in the maximum growth temperatures for VEE and EEE viruses appear to be due to the existence of a virus-induced, temperature-sensitive step in VEE virus synthesis.