Skin pustules and nodules caused by Actinomyces viscosus in a horse.

The research article highlights a case of an Arabian stallion affected by a persistent skin condition for two years which was finally attributed to the bacterium Actinomyces viscosus and successfully treated with a specific drug regimen.

Case Background and Clinical Signs

• The patient in question is a 12-year-old Arabian stallion, with a skin condition unresponsive to regular treatments for two years.
• The horse exhibited skin nodules and pustules primarily over its right lumbar muscles. These skin issues would eventually rupture and presumably cause discomfort or pain to the horse.

Diagnosis Methodology

• Anaerobic culturing, which is a method of growing bacteria that thrive in conditions lacking oxygen, was performed on the pustular content. This led to the identification of the causative agent – Actinomyces viscosus.
• A histologic examination, a microscopic analysis of physical structure of tissues, was carried out on samples obtained through biopsy. This revealed the presence of globular eosinophilic structures, a sign of an ongoing inflammatory response.

Treatment and Outcome

• Having determined the cause, the research team proposed a specific treatment regimen of three drugs. Isoniazid was administered at a rate of 8mg/kg body weight every 24 hours for 8 weeks, trimethoprim-sulfadiazine at a dose of 30 mg/kg every 24 hours for 8 weeks, and sodium iodide solution at a dose of 66 mg/kg either every 1, 2, or 4 weeks, for a total duration of 32 weeks.
• The multi-drug treatment plan effectively resolved the horse’s condition. Therefore, this case study provides a valuable reference for future similar cases.