Abstract
A small plaque (sp) and four temperature-sensitive (ts) mutants of western equine encephalomyelitis virus (WEEV) were obtained from a highly virulent field isolate (BFS-1703) after mutagenesis with 5-azacytidine or nitrosoguanidine or following undiluted passage in mosquito cell culture. Three ts mutants (158, 214, and 260) expressed stable ts phenotypes as determined both by six-hour leak yield and efficiency of plaquing (EOP) analyses. Progeny of ts mutant 214 grown at the nonpermissive temperature lacked hemagglutinin activity. The sp mutant (148) was as highly virulent as the wild-type virus (WTV) for newly hatched chickens (infected when 12 hours old), whereas the ts mutants were attenuated in their virulence for this host. Attentuation was correlated with lower viremia titers in 24-hour postinfection blood samples. The WTV and those mutants able to infect 21-day-old chickens produced nonlethal infections but the growth of ts 158 was apparently restricted in this high-temperature nonpermissive host. All ts mutants except ts 158 lost their ts phenotype after growth for 24 hours in newly hatched chickens and in duck embryonic cell culture (DECC) maintained at 42 degrees C.
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