The N and P genes facilitate pathogenicity of the rabies virus G gene

To explore the effects of different gene combinations on the pathogenicity of the rabies virus (RABV), six chimeric RABV mutants, rRC-HL(G), rRC-HL(NG), rRC-HL(PG), rRC-HL(NP), rRC-HL(NM) and rRC-HL(NPG), were constructed using a reverse genetic technique based on an avirulent parental rRC-HL strain and a virulent parental GX074 isolate. These mutants were intracerebrally inoculated into adult mice. The results indicated that 10² ffu and 10⁶ ffu of rRC-HL(G), rRC-HL(NG), rRC-HL(PG) and rRC-HL(NPG) were 100% lethal. In the case of intramuscular viral infection, none of the mice inoculated with 10²ffu of any of the RABV mutants, including GX074, died; at 10⁶ffu, rRC-HL(G) was lethal in 2/5 cases, rRC-HL(NG) was lethal in 1/5 cases and rRC-HL(PG) was lethal for 2/5 mice. The rRC-HL(NPG) mutant was fatal for 3/5 mice, as was the parental GX074. Furthermore, the LD₅₀ values of the chimeric RABV mutants were measured, with the results showing that the LD₅₀ values of both rRC-HL(NG) and rRC-HL(PG) were lower than that of rRC-HL(G), but higher than that of rRC-HL(NPG). Thus, the action of N + G, or P + G, or N + P + G gene combinations may be more pronounced than that of the G gene alone. Body weight changes and the clinical symptoms of the tested mice were consistent with pathogenicity. These data indicate that the N and P genes are involved in and facilitate the pathogenicity of the RABV G gene. These experiments provide further evidence that multi-gene cooperation is responsible for the virulence of RABV.