Investigation of nucleotide changes during attenuation of wild-type RS-12 mumps virus to vaccinal strain.

Introduction: Prior to implementation of vaccination against mumps disease, mumps virus (MuV) was the leading cause of virus-induced CNS disease. Following widespread use of mumps vaccine, the MuV-associated CNS complications, especially aseptic meningitis had dramatically reduced. The Iranian RS-12 strain is attended to incorporate in the domestic mumps vaccine. The aim of this study was to establish a standard seed lot system (using RS-12 strain) suitable for mass production of mumps vaccine, to determine the potencial attenuating mutations in the viral surface proteins. Methods: To optimize the condition of cultivation and preparation of standard seeds, several viral-yield affecting variables including multiplicity of infection (MOI), inoculation of virus to cell suspension vs. cell monolayer as cell substrate and filteration of harvested materials were evaluated. To determine the mutations, direct sequencing method was employed. Results: Cultivation method was successfully optimized and a standard seed lot system was established by inoculation of the RS-12 virus at a MOI of 1:10 to MRC-5 cell suspension and filteration of harvested materials following CPE observation. The F, SH and HN genes of the attenuated virus were sequenced in different stages of the prepared seeds and was deposited in the GenBank as RS-12 vaccine for the first time (Accession number HQ200192). Two potencial attenuating mutations in HN gene (413 T to C and 653 T to C) with the ability of differentiation of RS-12 wild-type from vaccine were detected. Discussion: in this study a stansard seed lot system was established, the potencial attenuating mutatios in HN gene were detected as a molecular marker of batch consistency and also for differentiation of attenuated and wild-type RS-12 strain of MuV. Key words: mumps, vaccine, RS-12.