[The Infectious and Pathogenic Characteristics of Rabies Virus Strain CTNCEC25]

To investigate the phenotypic characteristics of the strain of the rabies virus CTNCEC25, the strain of the China rabies virus CTN-1 adapted to primary chicken embryo cells (CECs), Vero cells, and mouse neuroblastoma N2a cells was inoculated with CTNCEC25 and parental CTN-1 strains to explore the cytopathic effect (CPE) and growth kinetics of CTNCEC25 on cultured cells. To determine the pathogenicity of CTNCEC25, suckling mice, adult mice, guinea pigs and rabbits were inoculated with CTNCEC25 via the intracerebral route and their survival monitored every day. Furthermore, the CTNCEC25 strain was passed serially in CECs for 20 passages and then 3 passages in the brains of suckling mice to determine phenotypic stability. CTNCEC25 achieved similar growth kinetics in Vero cells and N2a cells compared with parental CTN-1, but CTNCEC25 replicated more efficiently in CECs than the CTN-1 strain with a titer 72 h after infection reaching 10(7.5-7.6) FFU/mL, which was significantly higher than the 10(5.8) FFU/mL achieved by its parental strain, CTN-1. Moreover, CTNCEC25 induced apparent CPE in Vero cells, CECs and N2a cells. Analyses of intracerebral inoculation demonstrated that CTNCEC25 was attenuated profoundly in adult mice and was completely apathogenic to guinea pigs and rabbits, though it caused death in suckling mice. The CTNCEC25 strain proliferated steadily after serial passage in CECs and the brains of suckling mice, and remained avirulent in adult mice. These results suggest that CTNCEC25 is a highly attenuated and genetically stable strain of the rabies virus. CTNCEC25 replicated stably and efficiently in cultured cells and achieved high titers, so it could be a promising and safe vaccine strain for rabies prevention in China.