Nitric-zinc topical shows promise for equine aural plaques: full analysis

A newly published case series in Equine Veterinary Journal points to a potentially simpler way to manage equine aural plaques: topical nitric acid and zinc solution. In 12 horses with 20 affected ears treated at Swedish equine clinics, 17 ears reportedly went into complete remission after one to five applications of Oxalic® or Verrutop®, and the remaining three improved substantially, with no adverse effects observed. The authors conclude the nitric-zinc complex was safe and effective in this series, while also acknowledging important limitations, including the retrospective design, small sample size, absence of a control group, and lack of PCR or histologic confirmation. (publications.slu.se)

That matters because equine aural plaques have long been a management headache rather than a clean therapeutic win. The lesions are associated with papillomavirus infection, and major veterinary references note that black flies are thought to act as a mechanical vector. Horses may be asymptomatic, but some develop marked ear sensitivity that complicates routine handling and bridling. More recent epidemiologic work also suggests the condition is common in some populations: a 2024 study in Brazil found aural plaques in 41.5% of Mangalarga Marchador horses and 33.6% of Quarter Horses examined, with Equus caballus papillomavirus DNA detected in 90% of biopsied lesions and EcPV4 most frequently identified. (merckvetmanual.com)

The Swedish series covered cases seen from 2012 through 2022. According to the study summary, complete remission was achieved in 17 of 20 ears, and the remaining three ears improved enough that clinical discomfort was no longer observed. The treatment is notable because nitric-zinc complex solutions are already used in human wart care, giving the approach a translational rationale for papillomavirus-associated lesions. But the paper stops short of proving causality or superiority: lesions were diagnosed macroscopically, not confirmed by laboratory testing, and the study design cannot rule out selection bias or other confounders. (publications.slu.se)

The most relevant comparator in the literature is imiquimod. A 2010 open-label clinical trial found complete resolution in all 16 horses that completed treatment, but the tradeoff was substantial local inflammation, crusting, erosion or ulceration, and frequent need for restraint or sedation. In that study, 10 of 16 horses required sedation before each treatment, and owners identified treatment difficulty and horse discomfort as major drawbacks. Merck Veterinary Manual similarly notes that imiquimod can be effective, but the inflammatory response makes it difficult to use in practice. (conservancy.umn.edu)

There doesn't appear to be much published expert commentary yet on the new nitric-zinc report beyond literature listings, which is not surprising given how recently it appeared online in March 2026. Inference: if the no-adverse-effect signal holds up in broader use, that would likely draw attention from equine dermatology clinicians because it addresses the main practical weakness of imiquimod-based protocols rather than just lesion clearance. That inference is grounded in the contrast between the new case series and the established imiquimod literature, not in a direct expert quote. (vetlit.org)

Why it matters: For veterinary professionals, the study is less about declaring a new standard of care and more about expanding the conversation around treatable, quality-of-life-relevant ear disease. Aural plaques are often dismissed as cosmetic unless horses become head-shy, but the older imiquimod data and current references both support that some cases are clinically significant. A topical option that may require fewer applications, less inflammation, and potentially less sedation could improve compliance for pet parents and reduce handling stress for horses and staff. At the same time, the evidence base remains thin, so clinicians will still need to individualize decisions, discuss uncertainty clearly, and reserve stronger claims until prospective trials are available. (merckvetmanual.com)

What to watch: The key next questions are whether recurrence remains low over longer follow-up, whether the treatment performs similarly in larger and more diverse horse populations, and whether future controlled trials validate the apparent safety advantage over imiquimod. It will also be worth watching for protocols that clarify case selection, application intervals, pain control needs, and whether laboratory confirmation of papillomavirus status changes outcomes or treatment planning. (publications.slu.se)