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Basics ⬇

Outline

BASICS

Overview!!navigator!!

Aural plaques are whitish plaques on the inner pinnal surface of horses that are caused by EcPV.

Signalment!!navigator!!

  • Common in all sexes and breeds but rarely observed in horses <1 year old
  • Incidence ranges from 14.8% of Brazilian horses to 20–24% of horses in the USA
  • 85% of Brazilian farms had at least one horse affected

Signs!!navigator!!

  • Depigmented, well-demarcated papules and plaques covered with keratin deposits located on the concave pinnal surface. Lesions are single, multiple, or coalescing and may affect 1 or both pinna
  • Horses can be asymptomatic or may resent bridling or handling of the ears
  • Symptoms may be aggravated by biting flies

Causes and Risk Factors!!navigator!!

  • Lesions contain EcPV, with EcPV types 3, 4, 5, and/or 6 consistently identified in biopsies
  • Abrasions and biting flies, particularly black flies, are likely involved in viral transmission
  • Ear grooming is associated with an 8.6-fold increased risk of coalescing (severe) lesions
  • Increased horse density

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

Sarcoids—more often on the external surface of the pinna or at the margins of the ear. May coexist with aural plaques.

CBC/Biochemistry/Urinalysis!!navigator!!

N/A

Other Laboratory Tests!!navigator!!

N/A

Imaging!!navigator!!

N/A

Other Diagnostic Procedures!!navigator!!

Diagnosis is based on classic appearance and can be confirmed by biopsy.

Treatment ⬆ ⬇

TREATMENT

  • Aural plaques are not known to resolve without treatment. Horses without ear sensitivity do not require treatment
  • CO2 laser ablation has been used but long-term efficacy is unknown
  • Ear handling and ear clipping should be minimized in affected horses that are not being treated
  • Ears should be protected from biting flies to avoid aggravation of the condition

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

  • Topical imiquimod, an immune response modifier with antiviral activity, is the only drug shown to be consistently effective
  • Imiquimod 5% cream resolves the plaques in 87–88% of horses and clears the infection with EcPV in 71% of ears biopsied
  • Each lesion must be treated. Imiquimod is applied topically as a thin layer 2 or 3 times per week at least every other week until resolution, typically 3–4 months of every other week therapy (9–48 treatments). Alternatively, horses may be treated every 48 h for faster resolution (8–30 applications). A strong local inflammatory response is consistently observed with imiquimod due to its mechanism of action. The exudate and inflammation can make it difficult to handle and clean the ears prior to the next treatment. Sedation is often needed, particularly for the second or third treatment weeks. Inflammation generally resolves 7 days after the last treatment. Owners should be warned of the reaction and temporarily increased sensitivity due to local inflammation

Contraindications/Possible Interactions!!navigator!!

Imiquimod can cause inflammation of normal skin. No need to wash off the imiquimod until the next treatment is due.

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

  • Monitor for appropriate cleaning, application of imiquimod, and for complete resolution
  • Clients may have difficulty cleaning the area sufficiently prior to treatment, resulting in poor contact of the drug with the plaques. Sedation is required for subsequent treatment if the repeated treatment occurs before 7 days after the last application. Inflammation caused by imiquimod can make it difficult to determine if the plaque resolution has occurred. Discontinuation of treatment for 1–2 weeks allows for better evaluation. Reevaluation at 1 month post treatment is strongly recommended. Assume any whitish areas are residual plaques. Recurrence is possible but infrequent within the subsequent 2 years if the plaques were resolved and flies controlled

Prevention/Avoidance!!navigator!!

  • Not possible
  • Use of fly repellents with permethrin/pyrethrin (for quick insect knockdown) and piperonyl butoxide (as a pesticide synergist) with fly masks that provide ear coverage may help prevent development

Possible Complications!!navigator!!

  • Ear sensitivity and pain
  • Imiquimod can cause erosions or ulcers, particularly if applied in a thick layer. Erosions are more common in the first month of treatment. The severity of the reaction decreases as the plaques resolve

Expected Course and Prognosis!!navigator!!

  • Aural plaques persist without treatment
  • Post-treatment skin depigmentation may occur
  • Ear sensitivity and head shyness improves after resolution of plaques despite the inflammation and challenges with ear handling during treatment

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Conditions!!navigator!!

None known.

Age-Related Factors!!navigator!!

None known.

Zoonotic Potential!!navigator!!

None

Abbreviations!!navigator!!

EcPV = Equus caballus papillomavirus

Internet Resources!!navigator!!

University of Minnesota, Veterinarian instructions for Aldara. http://www.vetmed.umn.edu/centers-programs/clinical-investigation-center/completed-clinical-studies/veterinarian-instructions-aldara

Author(s) ⬆ ⬇

Author: Erin Malone

Consulting Editor: Gwendolen Lorch

Acknowledgment: The author and editor acknowledge the prior contribution of Sheila Torres.

Additional Further Reading ⬆

Click here for Additional Further Reading