Imported B3 genotype measles virus isolated in Fujian province

Objective: We isolated and identified the genotypes and molecular characteristics of the imported B3 measles virus (MeV) in Fujian province in 2018. Methods: Throat swab specimens were collected from clinically diagnosed measles patients and tested for viral RNA, using the real-time reverse transcription-polymerase chain reaction after the RNA extraction. Reverse transcription-polymerase chain reaction method was undertaken to amplify the 634 nucleotide acids of 3-terminal of the nucleoprotein gene. A phylogenetic tree was constructed and similarities in homology assessed. Results: We successfully isolated and obtained two measles virus strains and eighteen viral nucleic acid sequences. The Fujian strains were clustered within the same genotype group of WHO genotype B3 reference strains. Compared to the major circulating measles strain genotype B3 in the world, two Fujian strains MV18-41 and MV18-42 showed 100.0% nucleic acid homology to HongKong.CHN/35.18 strain which was isolated from Hong Kong in 2018. The remaining 16 Fujian strains showed the highest homology (99.9%) with the Mvs/Osaka.JPN/38.18/B3 strain isolated from Japan in 2018. Compared with other 23 WHO genotype reference strains, homology on both nucleotide and amino acid of the Fujian strain and the B1 genotype reference strain were the smallest, as 95.1%-95.4% and 95.3%, respectively. The differences of homology between the Fujian strain and H1 genotype reference strain were the largest, as 88.7%-89.0% and 87.3%, respectively. In addition, there were 13 mutation sites between the Fujian strain and the vaccine strain (Shanghai-191) at the 150 amino acid position of carboxy terminus on N protein, However, these sites did not cause functional changes in the protein region. Conclusions: In Fujian province, two strains of B3 genotype measles virus were obtained successfully, which were considered to be new genotype measles virus found in 2018. These findings showed it is necessary to strengthening the monitoring program on imported cases for better control and eliminate the measles virus.