Identity of tissue culture adapted Rift Valley fever virus (ZH501)

Rift Valley Fever (RVF) is still a threatening zoonotic disease with periodic reemergence in several countries. Egypt is endemic with RVF and uses an inactivated vaccine for control of the disease. Routine testing of the tissue culture adapted seed virus (ZH501-TC), to assess the effect of nucleotide mutations, is essential for the purpose of vaccine production. At the present work we have analyzed partial nucleotide and deduced amino acid sequence of amplified 745 bp product of M segment Gn ectodomain and checked virulence in mice. Allocation of ZH501-TC strain at the A designated lineage with the virulent parental RVFV isolated in 1977, ZH501 Egy Sh 77 indicates its genomic stability after passaging in tissue culture cells for vaccine preparation. Here we denoted a new missense nucleotide mutation A1312G corresponding to the amino acid mutation N371S, in current study the ZH501-TC  strain (MZ218760) compared to the parental virulent RVFV isolate ZH501 Egy Sh 77 ( previous sequence ) . That mutation enhanced ß sheet formation in ZH501-TC 367AQYASAYCS375 motif which might increase virus antigenicity. In addition, we have confirmed the presence of two sites of nucleotides substitutions; C1033T and A1206C, corresponding to two amino acids changes; T287I and S336R. Our study declared the false notion of the presence of one missense nucleotide mutation; A1252G corresponding to the amino acid mutation K351R, and two other silent nucleotide substitutions; T1257A and G1258C at the strain ZH501-VSVRI. Although we found these mutations, the virulence of the ZH501-TC strain was still present as approved by mice pathogenicity test.