Nucleotide and Amino Acid Changes in HN, F and SH genes of an Iranian Mumps Virus; RS-12, Following Attenuation to Vaccine Strain

Background and Aims: Wild-type RS-12 strain of mumps virus has been isolated from an Iranian patient and has been attenuated after several serial passages. This study was designed to determine nucleotide and amino acid substitutions in the HN, F and SH genes during attenuation of the wild-type virus. Materials and Methods: Required viral samples prepared at Razi Vaccine and Serum Institute. Viral RNA was extracted, targeted segments were amplified and sequenced and finally were analyzed using DNAMAN software. Results: No difference in nucleotide and deduced amino acid sequence of the F and SH genes was detected following attenuation of wild-type as compared to the vaccine strain, but four nucleotide changes in HN gene had occurred which had resulted in two nucleotide differences. Conclusions: Considering the HN nucleotide sequences and the deduced amino acid sequences, RS-12 wild-type and vaccine strains were distinguishable. Moreover, unique differences between RS-12 and some other vaccine strains existed. During serial passages of RS-12 strain for seed lot system preparation, no change in HN, F and SH genes occurred which -at least in some extents- proved the genetic stability of the attenuated RS-12 surface proteins. Potential attenuating mutations in other genes (N, P, M, L and even non-coding regions in 3′ and 5′ ends) should be investigated and confirmed using advanced methods.