Molecular Epidemiology of Bordetella pertussis Strains Isolated in Vietnam During 2015–2017

Abstract

Background: Whooping cough is a serious respiratory illness in infants caused by Bordetella pertussis. In spite of the vaccination program, the incidence rates of whooping cough per 100,000 population in Vietnam increased from 0.33 in 2015 to 0.58 in 2017. If this represents a pertussis resurgence, contributors may include pathogen adaptation, the spread of specific variants, vaccine failure, and failure to effectively treat cases and contacts. There has been little research in Vietnam on B. pertussis strains. Therefore, we investigated the molecular epidemiology of circulating B. pertussis strains in Southern Vietnam by applying multilocus sequence typing (MLST) for 7 housekeeping genes and 4 antigenic determinant genes as components in the acellular vaccine including prn, ptxP, ptxS1, and fim3. Methods: DNA was extracted from 15 isolates collected from 263 case patients during 2015–2017 and was subject to MLST using primers and cycling conditions from the Bordetella pubMLST website (www.Pubmlst.org/Bordetella/). The products were analyzed using BioEdit version 7.2.5 software and then were aligned and compared to reference sequences of each genotype in the database. The evolutionary relationship among sequence types (STs) from housekeeping genes was performed as a minimum spanning tree via the goeBURST algorithm, whereas the correlation of different variants from 4 antigenic determinant genes was built up and clarified with phylogenetic trees based on the UPGMA method by MEGA 7 program. Results: The 15 isolates were all classified as ST2 (100%) by MLST of housekeeping genes, and they belonged to a common global clonal group (Fig. 1). Sequencing of antigenic determinant genes prn2 – ptxP3 – ptxS1-1 – fim3-1 determined that all were identical to each another and the reference sequences (Fig. 2). Conclusions:B. pertussis isolates circulating in Southern Vietnam appeared to be the same as the common global strain. Few isolates were available for testing; therefore, continued surveillance is important to confirm these findings and to monitor population changes over time.

Funding: None

Disclosures: None