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

BACKGROUND: Equine aural plaque caused by equine papilloma viruses is common worldwide and affected horses can show severe clinical signs. Due to its viral aetiology, in some countries affected horses are not allowed to compete. Since lesions persist, showing no spontaneous regression, effective and safe treatment is required. Currently, the only treatment with consistent efficacy is imiquimod. Treatment time is prolonged and adverse effects are common. In humans, papilloma warts are successfully and safely treated with topical nitric-zinc complex solutions inducing a painless caustic effect. OBJECTIVES: To retrospectively evaluate the effectiveness and adverse effects of topical treatment with a nitric acid and zinc solution (Oxalic® or Verrutop®). STUDY DESIGN: Retrospective case series. METHODS: Records from horses with aural plaque diagnosed at the Equine Clinic of the University Animal Hospital and Equine Clinic, Täby, Sweden during 2012-2022 were reviewed. Included horses were treated topically with nitric acid and zinc solution (Oxalic® or Verrutop®), unilaterally or bilaterally every other week until remission. A successful outcome was defined as no remaining lesions at 12- to 28-month follow-up. RESULTS: Twelve horses were included, eight bilaterally affected. In total 20 ears were treated. Complete remission was seen in 17 ears (1-5 treatments, median 1.5). The three remaining ears substantially improved and clinical signs of discomfort were no longer observed. No adverse effects were seen. MAIN LIMITATIONS: Retrospective study, small sample size, not blinded and no control group included. Lesions were diagnosed by macroscopic appearance; no PCR for virus detection or histology was made. CONCLUSION: Topical nitric-zinc complex solutions are a safe and effective treatment for equine aural plaques.