Clusters of high transmission risk and time series for Equine Infectious Anemia in Brazil.

Overview

• This study mapped and analyzed the patterns and trends of Equine Infectious Anemia (EIA) cases reported in Brazil over an 18-year period, identifying key high-risk regions and temporal changes in disease incidence across different states and regions.

Introduction to Equine Infectious Anemia and Study Goals

• Equine Infectious Anemia (EIA) is a viral disease affecting horses, which can lead to significant health issues and economic losses in the equine industry.
• The study’s primary objective was to identify geographic clusters with higher risk of EIA transmission in Brazil and to analyze how the incidence of EIA changed over time from 2006 to 2023.
• Understanding spatial and temporal trends assists in improving disease surveillance and informing targeted control strategies under Brazil’s National Equine Health Program.

Data and Methodology

• Data Source: The study utilized reported EIA cases from the National Animal Health Information System (SIZ) in Brazil.
• Time Period: Data spanned from 2006 to 2023, covering 18 years of reported cases.
• Analysis Focus:
  • Spatial Analysis: Identifying clusters or hotspots where infection risk was higher.
  • Spatiotemporal Analysis: Understanding how these clusters changed or persisted over time.
  • Temporal Trend Analysis: Examining year-to-year changes in incidence rates within regions and states.

Key Findings

• Total Cases: 111,826 EIA cases were reported nationwide over the study period.
• Regional Distribution:
  • Northeast Region accounted for the largest proportion of cases at nearly 40%.
  • Central-West and North regions followed, contributing approximately 27.56% and 20.95% of cases respectively.
• State-Level Incidence:
  • Mato Grosso (Central-West) had the highest absolute number of cases (17.02%).
  • Sergipe (Northeast) had the fewest cases (0.36%).
  • When considering incidence risk relative to the horse population, Ceará, Roraima, and Maranhão showed extremely high risk rates, exceeding 6,700 cases per 100,000 horses, highlighting localized intense transmission.
• High-Risk Clusters: Identified in multiple states primarily across the North, Northeast, and parts of the Central-West regions, including Amapá, Pará, Maranhão, Roraima, Tocantins, Piauí, Amazonas, Ceará, Mato Grosso, Rondônia, Rio Grande do Norte, and Pernambuco.
• Temporal Trends:
  • Overall, Brazil showed a significant decreasing trend in EIA infection rates (average annual percentage change [AAPC] of -8.4%), indicating improved control or decreased transmission nationally.
  • Contrastingly, the South region exhibited an increasing trend in EIA incidence (AAPC of 6.5%), which requires targeted attention and investigation.

Implications and Importance

• The identification of geographic hotspots and temporal trends enhances understanding of where and when EIA poses the greatest risk, enabling resource prioritization.
• Recognition of regions with increasing trends, like the South, can prompt focused epidemiological investigations and tailored intervention strategies.
• Spatial and temporal surveillance is key to interrupting transmission chains and reducing the disease burden.
• The study supports the National Equine Health Program in Brazil by providing evidence to:
  • Develop or improve location-specific control measures.
  • Implement more efficient vaccination or testing programs.
  • Support policy decisions and deploy veterinary public health resources more effectively.

Conclusion

• This comprehensive study underscored persistent high-risk areas for EIA in Brazil, with notable geographic and temporal variability.
• The findings recommend continued and enhanced surveillance using spatial and temporal techniques to monitor EIA and adapt control measures dynamically.
• Such work is essential for reducing EIA transmission, safeguarding equine health, and minimizing economic impact in Brazil.