Whole Genome Sequence Analysis of < i > Salmonella < /i > Typhi Isolated in Thailand before and after the Introduction of a National Immunization Program

by Zoe A. Dyson, Duy Pham Thanh, Ladaporn Bodhidatta, Carl Jeffries Mason, Apichai Srijan, Maia A. Rabaa, Phat Voong Vinh, Tuyen Ha Thanh, Guy E. Thwaites, Stephen Baker, Kathryn E. Holt Vaccines againstSalmonella Typhi, the causative agent of typhoid fever, are commonly used by travellers, however, there are few examples of national immunization programs in endemic areas. There is therefore a paucity of data on the impact of typhoid immunization programs on localised populations ofS. Typhi. Here we have used whole genome sequencing (WGS) to characterise 44 historical bacterial isolates collected before and after a national typhoid immunization program that was implemented in Thailand in 1977 in response to a large outbreak; the program was highly effective in reducing typhoid case numbers. Thai isolates were highly diverse, including 10 distinct phylogenetic lineages or genotypes. Novel prophage and plasmids were also detected, including examples that were previously only reported inShigella sonnei andEscherichia coli. The majority ofS. Typhi genotypes observed prior to the immunization program were not observed following it. Post-vaccine era isolates were more closely related toS. Typhi isolated from neighbouring countries than to earlier Thai isolates, providing no evidence for the local persistence of endemicS. Typhi following the national immunization program. Rather, later cases of typhoid appeared to be caused by the occasional importation of common genotypes from nei...
Source: PLoS Neglected Tropical Diseases - Category: Tropical Medicine Authors: Source Type: research