Spatial analysis of human and livestock anthrax in Dien Bien province, Vietnam (2010–2019) and the significance of anthrax vaccination in livestock

Abstract

Anthrax is a serious zoonosis caused by Bacillus anthracis, which primarily affects wild herbivorous animals with spillover into humans. The disease occurs nearly worldwide but is poorly reported in Southeast Asian countries. In Vietnam, anthrax is underreported, and little is known about its temporal and spatial distributions. This paper examines the spatio-temporal distribution and epidemiological characteristics of human and livestock anthrax from Dien Bien province, Vietnam from 2010 to 2019. We also aim to define the role of livestock vaccination in reducing human cases. Historical anthrax data were collected by local human and animal health sectors in the province. Spatial rate smoothing and spatial clustering analysis, using Local Moran’s I in GeoDa and space-time scan statistic in SaTScan, were employed to address these objectives. We found temporal and spatial overlap of anthrax incidence in humans and livestock with hotspots of human anthrax in the east. We identified three significant space-time clusters of human anthrax persisting from 2010 to 2014 in the east and southeast, each with high relative risk. Most of the human cases were male (69%), aged 15–59 years (80%), involved in processing, slaughtering, or eating meat of sick or dead livestock (96.9%) but environmental and unknown exposure were reported. Animal reports were limited compared to humans and at coarser spatial scale, but in areas with human case clusters. In years when livestock vaccination was high (>~25%), human incidence was reduced, with the opposite effect when vaccine rates dropped. This indicates livestock vaccination campaigns reduce anthrax burden in both humans and livestock in Vietnam, though livestock surveillance needs immediate improvement. These findings suggest further investigation and measures to strengthen the surveillance of human and animal anthrax for other provinces of Vietnam, as well as in other countries with similar disease context.

Spatial epidemiology of human anthrax in Son La province, Vietnam, 2003–2022

“…Most of the cases aged from 15 to 54 years old (86.4%) with zero cases under 5 years of age. This result differs from other provinces in Vietnam such as Dien Bien and Ha Giang where 3.1% and 15.8% cases were under 5 years old, respectively (Luong et al., 2022, 2023). Additional investigations into the cultural factors associated with the involvement of males and adults in handling sick or dead animals in Son La as well as other provinces in the region are needed.…”

“…Most reported human anthrax cases were male (81.8%). The pattern in which males predominantly got infected was not uncommon in other studies in Vietnam or globally (Luong et al., 2022, 2023; Migisha et al., 2021; Mwenye et al., 1996; Parlak & Parlak, 2016). Most of the cases aged from 15 to 54 years old (86.4%) with zero cases under 5 years of age.…”

“…When combined human and animal anthrax cases were available from 2003 to 2022. Here, anthrax cases were reported using criteria for Vietnam's national disease surveillance and are described in previous studies from neighbouring provinces (Luong et al., 2022, 2023). Briefly, any case with clinical signs (humans or livestock) and/or reported symptoms (humans) were defined as anthrax.…”

“…The population for 2021 and 2022 was computed using the zonal‐estimated population for 2020 and annual population growth rates between 2019 and 2020 of each corresponding commune (a province average of 1% per year). The zonal statistic routine was performed in QGIS with the method described elsewhere (Barro et al., 2015) and previously verified its accuracy in Vietnam at the national and provincial level (Luong et al., 2022; Walker et al., 2022).…”

“…The results were mapped in QGIS. This approach was applied to similar anthrax data in a previous study for nearby Dien Bien province in northern Vietnam (Luong et al., 2022).…”