Assessment of the antiparasitic effectiveness of pyrantel pamoate in treatment of Strongylidae invasions in young horses – preliminary studies.

Overview

• This study evaluated how effective pyrantel pamoate is at treating Strongylidae parasite infections in young horses in Poland.
• Results showed limited effectiveness in spring, suggesting parasite resistance, but good effectiveness at the end of summer.

Background

• Strongylidae nematodes, common intestinal parasites in horses, are treated with pyrantel pamoate.
• Resistance of these parasites to pyrantel pamoate has been observed globally, but prior to this study, no data existed for horses in Poland.
• This study aimed to fill that gap by assessing pyrantel pamoate’s efficacy in young horses aged 1-2 years.

Study Design and Methods

• The study involved both male and female horses aged between 1 and 2 years.
• Two seasonal periods were selected for the study: spring and late summer.
• Fecal samples were collected twice per horse: 24 hours before deworming and 14 days after treatment.
• Parasite egg counts were measured using two laboratory methods:
  • McMaster’s technique – a quantitative method for counting eggs per gram (EPG) of feces.
  • Combined sedimentation-flotation – a qualitative and quantitative method enhancing parasite detection.
• Effectiveness was evaluated by the Fecal Egg Count Reduction Test (FECRT), which calculates the percentage reduction in egg counts after treatment.

Key Findings

• Spring Results:
  • Average pre-treatment EPG across horses was 1354.54.
  • Post-treatment EPG reduced to 485.
  • Overall FECRT was 67.45%, indicating moderate reduction in parasite eggs.
  • By age group:
    • One-year-old horses started with higher EPG (1565.38) compared to two-year-olds (1050).
    • FECRT was 69.78% in one-year-olds and 62.43% in two-year-olds.
  • According to World Association for the Advancement of Veterinary Parasitology (WAAVP) standards, FECRT under 90% is suggestive of resistance, implying the presence of pyrantel pamoate-resistant Strongylidae in spring.
• Late Summer Results:
  • Pre-treatment EPG was higher than spring at 1954.54.
  • Post-treatment, only two horses showed any strongyle eggs, demonstrating very effective parasite control.
  • FECRT was very high at 99.53%, indicating near-complete elimination of egg shedding.
  • By age group:
    • One-year-olds had an average pre-treatment EPG of 2103.85 with a FECRT of 99.27%.
    • Two-year-olds had an EPG of 1738.89 with a perfect 100% FECRT.
  • This suggests no resistance or much higher drug efficacy at the end of summer.

Interpretation and Implications

• The lower efficacy in spring could be due to:
  • Seasonal changes in parasite biology or horse immune responses.
  • Emergence or prevalence of pyrantel-resistant Strongylidae populations during spring.
• The high efficacy in late summer suggests:
  • Either reduced parasite resistance in this season or other factors enhancing pyrantel effectiveness.
  • Recommended treatment timing might consider seasonal variations to optimize control.
• These findings highlight the importance of monitoring anthelmintic resistance locally.
• This is the first study investigating pyrantel pamoate effectiveness in horses in Poland, filling a significant knowledge gap.
• The evidence supports cautious use of pyrantel pamoate and suggests the need for regular efficacy monitoring and potential integration of alternative control strategies in spring.

Conclusion

• Pyrantel pamoate shows limited antiparasitic effectiveness against Strongylidae in young horses during spring in Poland, likely due to resistance.
• In contrast, it remains highly effective in late summer.
• Future parasite management in horses in Poland should consider this seasonal variation and potential resistance development.