Measles Epidemics Among Children in Vietnam: Genomic Characterization of Virus Responsible for Measles Outbreak in Ho Chi Minh City, 2014

BACKGROUND Measles remains poorly controlled in Southeast Asia, including Vietnam. OBJECTIVES The aim of this study was to characterize genes of virus responsible for a measles outbreak among children in Vietnam in 2014. STUDY DESIGN Throat swab samples were collected from 122 pediatric patients with suspected measles. Furthermore, peripheral blood mononuclear cells (PBMCs) from 31 of these cases were also collected. Measles virus (MV) RNA was obtained directly from the clinical specimens, amplified by PCR, and then the N and H genes were sequenced. RESULTS MV RNA was detectable in throat swabs from all 122 patients tested. Positive-strand viral RNA, which indicates the intermediate replicative form of MV, was also detected in PBMCs from all 31 cases from whom these cells were collected. One hundred and eighteen strains with the N gene were obtained by RT-PCR and sequenced. Using phylogenetic analysis with measles reference sequences, all of the Vietnamese strains were found to be genotype D8. However, all strains formed a distinct cluster within the genotype D8 group (D8-VNM) suggesting their own lineage. This distinct cluster was supported by a branch with a 99% bootstrap value and 3.3% nucleotide divergence in the N-450 region of the N gene from the D8 reference strain. Notably, all of the D8-VNM variant strains represented unique amino acid sequences consisting of R442, S451 and G452 in the N-450 region of the N gene. CONCLUSIONS Measles viruses responsible for outbreaks in Southern Vietnam belonged to a genotype D8 variant group which had unique amino acid sequences in the N gene. Our report provides important genomic information about the virus for measles elimination in Southeast Asia.