Journal of Vaccines & Vaccination

Abstract

ZH501-VSVRI: Is it Still the Best Choice for Vaccination Against Rift Valley Fever in Egypt?

Mohamed H Atwa, Ibrahim M El-Sabagh, Haitham M Amer, Samy Saad, Ausama A Yousif and Mohamed A Shalaby

ZH501 strain of Rift valley fever virus (RVFV) was originally isolated from a human patient during the outbreak of 1977 in Egypt. This virus strain was used since 1980 for preparation of an inactivated RVF vaccine at Veterinary Serum and Vaccine Research Institute (VSVRI), Egypt. Two subpopulations of ZH501 with a single nucleotide polymorphism (A/G) at nucleotide position 847 of Gn gene of M segment have been described. This nucleotide substitution affected significantly RVFV virulence in the mouse model. In this report, the genetic makeup of the Gn gene of ZH501-VRVSI vaccine virus stock was analyzed for verification of its safety and stability. Plaque assay of the vaccine stock virus revealed the presence of two populations that produced different plaque forms. The viruses that developed large plaques resembling those produced by the virulent virus strains were isolated for genetic analysis. Comparison of the Gn gene nucleotide sequence of the isolated viruses with those of the wild-type ZH501 and other reference strains identified five nucleotide substitutions, of which three are capable to induce amino acid changes in the mature protein. Protean analysis suggested a potential change in the three dimensional structure of the Gn protein in relation to the parent strain. The results of this study throw light on the changes occurred in the master seed virus used for preparation of RVFV vaccine in Egypt. Further studies focusing on the other gene segments of ZH501-VSVRI are required to conclude is it still the best choice for vaccination against RVF in Egypt.