Spatial and phylogenetic patterns reveal hidden infection sources of Bacillus anthracis in an anthrax outbreak in Son La province, Vietnam.

Bacillus anthracis, the bacterial cause of anthrax, is a zoonosis affecting livestock and wildlife often spilling over into humans. In Vietnam, anthrax has been nationally reportable since 2015 with cases occurring annually, mostly in the northern provinces. In April 2022, an outbreak was reported in Son La province following the butchering of a water buffalo, Bubalus bubalis. A total of 137 humans from three villages were likely exposed to contaminated meat from the animal. Early epidemiological investigations suggested a single animal was involved in all exposures. Five B. anthracis isolates were recovered from human clinical cases along with one from the buffalo hide, another from associated maggots, and one from soil at the carcass site. The isolates were whole genome sequenced, allowing global, regional, and local molecular epidemiological analyses of the outbreak strains. All recovered B. anthracis belong to the A.Br.001/002 lineage based on canonical single nucleotide polymorphism analysis (canSNP). Although not previously identified in Vietnam, this lineage has been identified in the nearby countries of China, India, Indonesia, Thailand, as well as Australia. A twenty-five marker multi-locus variable number tandem repeat analysis (MLVA-25) was used to investigate the relationship between human, soil, and buffalo strains. Locally, four MLVA-25 genotypes were identified from the eight isolates. This level of genetic diversity is unusual for the limited geography and timing of cases and differs from past literature using MLVA-25. The coupled spatial and phylogenetic data suggest this outbreak originated from multiple, likely undetected, animal sources. These findings were further supported by local news reports that identified at least two additional buffalo deaths beyond the initial animal sampled in response to the human cases. Future outbreak response should include intensive surveillance for additional animal cases and additional molecular epidemiological traceback to identify pathogen sources.

A case-control study of agricultural and behavioral factors associated with leptospirosis in Vietnam.

INTRODUCTION: Leptospirosis is a neglected disease in Vietnam. Until now, there has been limited knowledge about risk factors of this disease in Vietnam. The study was carried out to identify agricultural and behavioral factors associated with the transmission of leptospirosis in Vietnam. METHODS: This matched retrospective hospital-community-based case-control study was conducted from 1 October 2018 to 31 October 2019. We recruited cases from 11 selected government hospitals in three provinces of Vietnam, while controls were selected from the same communes of cases and matched by age (± 2 years) and sex. Microscopic agglutination test (MAT) and enzyme-linked immunosorbent assay (ELISA) were applied to determine confirmed cases, while only MAT was used to identify controls with a single high MAT titer < 1:100. RESULTS: 504 participants (252 cases and 252 controls) were identified. Cultivating (OR 2.83, CI 1.38-5.79), animal farming (OR 8.26, CI 2.24-30.52), pig owners (OR 10.48, CI 5.05-21.73), cat owners (OR 2.62, CI 1.49-4.61) and drinking unboiled water (OR 1.72, CI 1.14 -2.59, p = 0.010) were significantly associated with human leptospirosis in Vietnam. Hand washing after farming/ gardening (OR 0.57, CI 0.38-0.86, p = 0.007) and bathing after farming, gardening, contact with cattle and poultry (OR 0.33, CI 0.19-0.58, p = 0.000) were determined as protective factors for this disease. CONCLUSIONS: In short, the case-control study has revealed the risks in agricultural and animal practices and protective behavioral factors related to human leptospirosis in Vietnam. The findings suggested promotion of communication and health education programs targeting health behaviors in daily life and agricultural practices. Using personal protective equipment such as gowns, gloves, and boots during agricultural practices, especially cultivating and animal farming, is most recommended.

Characteristics of human leptospirosis in three different geographical and climatic zones of Vietnam: a hospital-based study.

BACKGROUND: To our knowledge, this study is the first report on the seroprevalence of human leptospirosis and its epidemiological profile in 3 different geographical and climatic zones of Vietnam. METHODOLOGY: A hospital-based surveillance in 11 public hospitals in 3 provinces in Vietnam enrolled 3,815 patients with suspected leptospirosis. Two consecutive enzyme-linked immunosorbent assay IgM and a single microscopic aggregation test were applied at a 1:100 to 1:800 dilution for probable or confirmed cases. RESULTS: The findings showed that of the 3,815 suspected cases, 68 (1.8%) were Leptospira-confirmed and 248 (6.5%) probable cases, whereas more than a third were positive for acute ELISA-IgM sera. Furthermore, 20 different serovars were found, of which Wolffi (14.2%), Hebdomadis (13.8%), and Icterohaemorrhagiae (12.6%) were the most predominant. The ratio of probable and confirmed cases of leptospirosis between females and males was 1.4:1, and their clinical manifestation was not specific. Cases were more likely to be detected in groups that are farmers, pet raising or livestock farming, of working age, practicing either wading in mud or walking barefoot, or exposed to heavy rainfall. CONCLUSIONS: Analysis of human leptospirosis has indicated fairly high seroprevalence and diversity of Leptospira serovars circulating in all studied geographical zones in Vietnam. The findings suggest an imperative need for effective measures of disease prevention, especially in high-risk groups.