Approaching equine infectious anemia in regions dominated by grade-working animals – a case of Pará, a state in the Brazilian Amazon.

Overview

• This study investigates the prevalence and risk factors of Equine Infectious Anemia (EIA) in Pará, a state in the Brazilian Amazon dominated by grade working equids.
• It assesses how current control strategies based on testing and removing infected animals may be ineffective in such settings, proposing the need for alternative approaches.

Background and Objectives

• Equine Infectious Anemia (EIA): a contagious viral disease affecting horses, mules, and donkeys, typically controlled by identifying infected animals via serological tests and removing them to prevent spread.
• Problem in Pará: The majority of equids are grade working animals (used for labor, often in lower-income settings), and conventional control measures might not be practical or effective.
• Study Aim: To analyze the epidemiological situation of EIA in Pará, evaluate the effectiveness of current control strategies, and suggest context-relevant adjustments or new methods.

Methods

• Geographic Division: Pará state was split into five distinct regions, representing varying farming conditions and animal populations.
• Farm and Animal Sampling: In each region, farms were randomly selected. On the farms, a set number of equids (horses, mules, and donkeys) were randomly sampled to ensure representative results.
• Diagnostic Testing: The Agar Gel Immunodiffusion (AGID) test was used to detect antibodies against the EIA virus, indicating infection.
• Questionnaires on Risk Factors: Administered to farm operators to determine practices or conditions that might contribute to disease spread (e.g., herd size, water sources).

Findings

• Sample Size: 2,718 equids from 654 farms were tested across the state.
• Prevalence Rates:
  • Farm-level prevalence: 34.5% (about one-third of farms had infected animals).
  • Animal-level prevalence: 15.8% (about one in six equids tested positive).
  • Significant differences in infection rates between the five regions.
• Risk Factors:
  • Farms with 11 or more equids had a higher likelihood of infection (Odds Ratio [OR] = 2.32), indicating larger herds increase transmission risk.
  • Sharing water sources with other farms increased infection risk (OR = 1.76), suggesting communal water points facilitate disease spread.
• Surveillance Sensitivity: The average sensitivity of the surveillance system to detect infected farms was very low (0.92% to 1.14%), insufficient to control or eliminate the disease.

Implications and Recommendations

• Limitations of Current Control Strategies:
  • The existing strategy of testing and removing infected equids is inadequate in Pará’s context due to high prevalence and socio-economic factors.
  • Low sensitivity surveillance means many infected farms remain undetected, perpetuating endemic disease levels.
• Reassessment Needed: The study highlights the need to reassess EIA control strategies tailored towards:
  • The realities of regions dominated by working grade animals whose removal is often economically unfeasible.
  • Improving surveillance sensitivity and possibly integrating alternative control measures such as education, management changes, or novel testing approaches.
• Broader Relevance: Although focused on Pará, findings and recommendations may apply to other regions worldwide with similar agricultural and socio-economic settings.

Conclusion

• This study provides crucial epidemiological data on EIA in a challenging context where typical control methods may fail.
• It calls for context-specific strategies to manage and reduce EIA impact on working equids vital for livelihoods, ensuring sustainable disease control in developing regions.