Spatial clusters of human and livestock anthrax define high-risk areas requiring intervention in Lao Cai Province, Vietnam 1991-2022.

Overview

• This study examined the patterns and spatial clusters of human and livestock anthrax in Lao Cai Province, Vietnam from 1991 to 2022.
• The research identified seasonal peaks, vaccination coverage gaps, and high-risk areas needing targeted interventions to better control and prevent anthrax outbreaks.

Introduction and Background

• Anthrax is a zoonotic disease, meaning it can be transmitted from animals to humans.
• It is especially prevalent in low and middle-income countries, where disease awareness is low and livestock vaccination coverage is generally insufficient.
• Lao Cai Province in northern Vietnam has a history of anthrax cases but experienced an apparent absence of reported cases in 2009, despite neighboring regions continuing to report infections.
• The study was motivated by the need to understand the disease trends in this province, assess vaccination efficacy, and identify areas that require focused control efforts.

Objectives of the Study

• Describe the seasonal pattern of anthrax outbreaks between 1991 and 2008 in Lao Cai.
• Compare livestock anthrax vaccine coverage to the actual disease occurrence from 1991 to 2022.
• Delineate spatial clusters or high-risk areas for human and livestock anthrax to guide enhanced local disease surveillance and control measures.

Methodology

• Data Collection:
  • Anthrax case data for humans and livestock collected from 1991 to 2022.
  • Livestock vaccine coverage data spanning the same period.
• Seasonal Analysis:
  • Examined temporal distribution of cases and identified peak months of incidence.
• Spatial Analysis:
  • Used SaTScan software with a Poisson model considering 25% of the population at risk to detect spatial clusters of anthrax cases.
  • Population data was derived using zonal statistics routines.
  • Generated maps of cumulative incidence and case counts for both human and livestock anthrax using QGIS geographic information system software.

Key Findings

• Seasonality:
  • Anthrax incidence peaked between May and October each year.
• Animal Reservoirs:
  • Buffalo, domestic cattle, and horses accounted for 75% of anthrax cases in animals.
  • Horse anthrax was particularly more common in Lao Cai compared to neighboring provinces and often coincided with years of human anthrax deaths.
• Vaccination Coverage:
  • Livestock vaccination coverage was consistently low, under 30% across the province.
  • Years with better control of anthrax (1998-2003) coincided with increased vaccine coverage above 20%.
• Spatial Clusters:
  • Significant clusters of both human and livestock anthrax were detected in three districts: Muong Khuong, Bao Thang, and Bac Ha.
  • These areas represent high-risk zones requiring focused surveillance and intervention.

Implications and Recommendations

• The study underscores the need for sustained and improved vaccination programs targeting livestock to reduce incidence.
• Public health and veterinary authorities should concentrate efforts on the identified high-risk districts with enhanced surveillance and targeted interventions.
• Coordination and communication should be established with neighboring provinces to adopt a regional approach for anthrax control due to the transboundary nature of the disease.
• Increasing public awareness and education about anthrax risks and prevention strategies is also essential.

Conclusion

• The research successfully mapped the seasonal and spatial characteristics of anthrax in Lao Cai Province over three decades.
• It identified critical gaps in vaccination and pinpointed districts with recurrent outbreaks, emphasizing priority areas for intervention.
• Overall, the findings support integrated surveillance, improved vaccine coverage, and regional cooperation as effective measures to control anthrax in this endemic area.