Actinomyces species as a cause of abscesses in nine horses.
Authors: Fielding C L, Magdesian K G, Morgan R A, Ruby R E, Sprayberry K A
Journal: The Veterinary record
Summary
# Editorial Summary: Actinomyces-Associated Abscesses in Horses Fielding and colleagues examined nine cases of bacterial abscess formation caused by Actinomyces species, an opportunistic pathogen that had received limited clinical attention in equine practice. The research team retrospectively analysed clinical records and microbiology results across a range of ages (1–11 years), using DNA sequencing to confirm species identification where available. Actinomyces presented predominantly as submandibular and retropharyngeal abscesses, typically cultured as a pure isolate with a notable seasonal clustering in autumn months; whilst conventional treatment combining antimicrobials and surgical drainage resolved most cases, recurrence occurred in a subset of horses, and those with submandibular involvement frequently developed persistent fibrotic scar tissue. This work highlights an underrecognised cause of deep head and neck abscesses that may warrant consideration when standard pathogens are not isolated, particularly in horses presenting during autumn, and suggests that clinicians should counsel owners on the potential for incomplete resolution and cosmetic complications even following successful drainage and antibiotic therapy. The findings underscore the value of comprehensive microbial culture and identification—including molecular techniques—in cases where clinical response to routine treatment is suboptimal.
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Practical Takeaways
- •Actinomyces should be considered as a differential diagnosis for submandibular and retropharyngeal abscesses in horses, particularly in autumn
- •Drainage combined with appropriate antimicrobial therapy is the primary treatment approach, but long-term scar tissue formation may limit cosmetic and functional outcomes
- •Recurrence of Actinomyces abscesses can occur even with standard treatment protocols, necessitating close monitoring during recovery
Key Findings
- •Nine horses aged 1-11 years presented with Actinomyces-caused abscesses, most commonly in submandibular and retropharyngeal regions
- •Actinomyces was cultured as sole isolate in most cases and showed seasonal prevalence in autumn months
- •Treatment with antimicrobials and drainage was partially effective, but recurrence occurred in some cases
- •Submandibular abscess cases resulted in residual scar tissue that persisted in some horses despite treatment