Topical treatment of equine aural plaques with nitric acid and zinc solution.

Overview

• This research investigates the effectiveness and safety of using a topical nitric acid and zinc solution to treat equine aural plaques caused by papilloma viruses.
• The study retrospectively analyzed clinical cases of horses treated with this solution and evaluated treatment outcomes over a long follow-up period.

Introduction and Background

• Equine aural plaques are lesions on horses’ ears caused by equine papilloma viruses, commonly seen worldwide.
• These lesions can cause severe clinical symptoms and potentially disqualify affected horses from competing in some countries due to their viral origin.
• Unlike some viral conditions, equine aural plaques typically do not regress spontaneously and require effective treatment to resolve.
• Current standard treatment with imiquimod is effective but involves prolonged treatment durations and frequent adverse effects.
• In human medicine, papilloma warts have been successfully treated using topical nitric-zinc complex solutions, which produce painless caustic effects.

Study Objective

• The main goal was to retrospectively evaluate the use of topical nitric acid and zinc solutions (commercially Oxalic® or Verrutop®) for treating equine aural plaques.
• This involved assessing both treatment effectiveness—measured by remission of lesions—and any associated adverse effects.

Methods

• Design: Retrospective case series review.
• Setting: Equine Clinic of the University Animal Hospital and Equine Clinic, Täby, Sweden.
• Period: Cases between 2012 and 2022 were reviewed.
• Inclusion criteria: Horses diagnosed visually with aural plaques and treated with the topical nitric acid and zinc solution either on one or both ears.
• Treatment protocol: Application every other week until lesions resolved.
• Outcome measure: Complete remission defined as no visible lesions on follow-up 12 to 28 months after treatment.

Results

• Total horses included: 12, with 8 horses having plaques on both ears (20 ears treated in total).
• Complete remission achieved in 17 of 20 ears after 1 to 5 treatments (median of 1.5 treatments).
• Remaining 3 ears showed significant improvement, and horses no longer exhibited discomfort symptoms.
• No adverse effects were reported throughout the treatment course.

Conclusions

• Topical nitric-zinc complex solutions appear to be a safe and effective way to treat equine aural plaques.
• Compared to imiquimod, this treatment may offer faster resolution without adverse effects although this was not directly compared in the study.
• Limitations include:
• Retrospective nature of the study.
• Small sample size.
• Lack of blinding and absence of a control group.
• Diagnosis was based on macroscopic appearance without confirmatory PCR or histological tests to detect the virus, which could affect diagnostic certainty.
• Despite limitations, findings suggest that nitric acid and zinc solution might be a promising treatment option for equine aural plaques warranting further controlled investigation.