Efficacy of mass antimicrobial treatment of foals with subclinical pulmonary abscesses associated with Rhodococcus equi.
Authors: Venner M, Astheimer K, Lämmer M, Giguère S
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary Rhodococcus equi pneumonia represents a significant challenge on endemic farms, yet the evidence base for treating subclinical disease remains unclear; this 2013 study investigated whether prophylactic antimicrobial therapy genuinely benefits foals with small ultrasonographic pulmonary abscesses (5–10 cm diameter). Researchers conducted a randomised, double-blinded, controlled trial across 108 affected foals, comparing five groups: tulathromycin monotherapy, doxycycline alone, doxycycline-rifampin combination, azithromycin-rifampin combination, and placebo, with blinded clinical and ultrasonographic assessment throughout. Remarkably, 88% of placebo-treated foals recovered spontaneously without intervention, and disease progression rates did not differ significantly between any treatment group, though azithromycin-rifampin shortened median treatment duration from 73 to 46 days without improving lesion resolution. These findings suggest that routine antimicrobial treatment of subclinical small pulmonary abscesses offers no clear clinical advantage over expectant management, challenging the empirical practice widely adopted on R. equi-endemic farms and raising important questions about unnecessary antimicrobial exposure, cost-effectiveness, and potential resistance development in foal populations.
Read the full abstract on PubMed
Practical Takeaways
- •Do not automatically treat foals with small subclinical pulmonary lesions (5-10 cm) identified on ultrasound—most will self-resolve without medication
- •Reserve antimicrobial therapy for foals showing clinical signs of disease progression; empiric mass treatment on endemic farms is unnecessary and exposes healthy foals to unnecessary medication
- •If treatment is deemed necessary, azithromycin-rifampin may shorten treatment duration, but does not accelerate lesion resolution compared to watchful waiting
Key Findings
- •88% of placebo-treated foals (22/25) recovered without antimicrobial treatment
- •Disease progression rates did not differ significantly between any treatment groups (P > 0.05)
- •Azithromycin-rifampin shortened median treatment duration to 46 days versus 73 days for placebo, but ultrasonographic lesion resolution time was not significantly different between groups
- •Mass antimicrobial treatment of foals with subclinical pulmonary abscesses <10 cm does not provide clear benefit over placebo