# Expanding the molecular epidemiology of melioidosis in North Central Vietnam

## TL;DR

This study explores the spread and genetic diversity of melioidosis in North Central Vietnam by analyzing clinical, soil, and animal isolates of the bacteria Burkholderia pseudomallei.

## Contribution

The study provides new insights into the molecular epidemiology of melioidosis in Vietnam, identifying novel bacterial strains and their potential transmission patterns.

## Key findings

- Fifteen sequence types (STs) were identified, including four new STs from clinical isolates.
- ST 41 was the most common clinical strain, found throughout Ha Tinh province and recovered from soil a year later.
- Genomic analysis revealed unique gene sets in clinical isolates that may relate to local virulence mechanisms.

## Abstract

Cases of melioidosis have been recorded for many years in Vietnam though it is still not a nationally reportable disease in Vietnam. More research is needed to understand the disease ecology and public health impacts of melioidosis in the country. To this aim, broadening the knowledge base of strains and epidemiology of infections in relation to genotypes present in the soil reservoir can tell us about the propensity of Burkholderia pseudomallei genotypes to transmit from soil to humans. Thirty-five clinical B. pseudomallei isolates, ten from soil, one from swine, and one from a bear were collected by the Institute of Microbiology and Biotechnology, Vietnam National University and sequenced at the National Institute of Hygiene and Epidemiology in Hanoi. The clinical strains were isolated from melioidosis patients from Ha Tinh in each month of 2020 (except July). There were 15 STs identified and four of the clinical isolates were new sequence types (ST) as determined by traditional seven marker multi-locus sequence typing (MLST) analysis. Twenty of the thirty-five (57%) clinical strains isolated in this study were ST 41, with ST 41 isolates obtained throughout the year and across Ha Tinh province with core genome (cg) MLST identifying finer scale differences. ST 41 was recovered from one soil sample approximately 1 year after the clinical isolates. cgMLST analysis and whole genome SNP analysis revealed nucleotide differences among strains in Ha Tinh historically contextualizing them in Vietnam and globally. As melioidosis moves towards a reportable disease in Vietnam, molecular epidemiological methods can connect human, veterinary, and environmental genotypes of concern.

The disease melioidosis has been intensely studied in Thailand and Northern Australia while many other locations have faced a lack of investigation, including other countries in Southeast Asia. Among the lesser studied areas is Vietnam. The bacterium that causes melioidosis, Burkholderia pseudomallei, can cause severe infections and is a public health concern in wet tropical locations around the world. This study takes a detailed molecular epidemiological look at clinical, soil, and veterinary B. pseudomallei isolates from North Central Vietnam. The isolates were whole genome sequenced which revealed STs shared among soil, veterinary, and clinical B. pseudomallei strains. Clinical sequence types were heavily enriched for isolates that shared unique gene sets that could indicate geographically specific bacterial virulence mechanisms.