Retrospective serological evidence of exposure to selected equine viruses in horses from Indigenous communities of Costa Rica, 2011.

Overview

• This study retrospectively analyzed blood samples from horses in Costa Rican Indigenous communities collected in 2011 to detect past exposure to various equine viruses.
• The research provides baseline data on the prevalence of antibodies against multiple equine viruses, highlighting the presence and distribution of these pathogens among horses important for local livelihoods.

Background and Rationale

• Horses play a critical role in transportation and daily life within Indigenous communities in Costa Rica.
• Despite their importance, there is limited information about the horses’ exposure to infectious viral diseases.
• Understanding viral exposure is essential for animal health, disease prevention, and safeguarding livelihoods.

Study Design and Sample Collection

• A retrospective cross-sectional serosurvey was conducted using stored serum samples.
• Samples were collected from 278 horses spanning four Indigenous communities: Alto Pacuare, Amubre, Paso Marcos, and Vereh.
• Sampling occurred between March and October 2011.
• Serological testing was performed in 2014 on these archived samples to assess antibody presence, indicating previous exposure.

Viruses Tested and Testing Methods

• The viruses evaluated included:
  • West Nile virus (WNV)
  • Equine herpesvirus types 1 and 4 (EHV-1, EHV-4)
  • Influenza A virus
  • Equine arteritis virus (EAV)
  • Equine infectious anemia virus (EIAV)
• Commercial immunodiffusion and enzyme-linked immunosorbent assay (ELISA) kits were used for antibody detection.
• The number of sera tested for each virus varied due to limited sample availability.

Key Findings: Seroprevalence Estimates

• West Nile Virus (WNV):
  • 58.9% seropositivity overall (139/236 samples).
  • Highest in Amubre community with 83.3% positive horses.
• Equine Herpesvirus-4 (EHV-4):
  • Very high seropositivity at 91.2% (125/137 samples), indicating widespread exposure.
• Equine Herpesvirus-1 (EHV-1):
  • Low seroprevalence found in 6.6% (9/137 samples).
• Influenza A Virus:
  • Detected at low frequency, 5.1% (12/237 samples).
• Equine Arteritis Virus (EAV):
  • Low seroprevalence of 3.0% (7/236 samples).
• Equine Infectious Anemia Virus (EIAV):
  • Moderate seroprevalence at 16.6% (35/211 samples).
  • Highest proportion found in Paso Marcos community at 23.8%.

Statistical and Comparative Analysis

• Statistical tests (Pearson’s chi-square or Fisher’s exact test) were used to assess differences in seropositivity among communities.
• Significant differences in exposure rates among communities were observed specifically for:
  • West Nile virus
  • Influenza A virus
  • Equine herpesvirus-4
• These differences suggest variations in virus circulation or exposure risk factors across the Indigenous communities studied.

Interpretation and Implications

• The data provide a historical perspective on virus exposure among horses in these indigenous areas dating back to 2011.
• Because the samples are older, the results do not necessarily reflect current infection or circulation status of these viruses.
• These findings establish a serological baseline against which future surveillance data can be compared.
• Demonstrates the importance of including underserved Indigenous horse populations in disease monitoring and prevention programs to better protect animal health and community livelihoods.
• Highlights the need for ongoing surveillance and targeted veterinary support in these regions.