Chemically induced temperature-sensitive mutants of dengue virus type 2: comparison of temperature sensitivity in vitro with infectivity suckling mice, hamsters, and rhesus monkeys.

A series of temperature-sensitive (ts) mutants of dengue virus type 2 (DEN-2, TH-36 isolate) were induced by treatment with 5-azacytidine. These mutants and parental viruses were compared for the ts trait and/or attenuation in four systems: primary hamster kidney cells, suckling mice, golden Syrian hamsters, and rhesus monkeys. Seven clones judged to possess the ts trait in virto demonstrated a variety of patterns in vivo. On initial isolation, five of seven ts mutants exhibited reduced mouse lethality. The remaining two mutants possessed parental levels of mouse lethality. In hamsters, neither ts mutant nor parental viruses replicated very well, and then only when inoculated intracerebrally. Studies in rhesus monkeys indicated that all seven ts clones and parental viruses were capable of inducing abtibody responses; however, ts-1 and ts-2 failed to produce detectable viremia. After challenge with parental virus, all vaccinated monkeys demonstrated rapid secondary-type antibody response. Reversion from ts to ts(+) was confirmed to ts-1 in mice and ts-3 in monkeys, and was strongly suspected in several other instances.