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Basics ⬇

Outline

BASICS

Overview!!navigator!!

  • Papillomas commence as benign proliferative epithelial neoplasms associated with the presence of EcPV and may occasionally progress to malignancy
  • Third most common cutaneous equine neoplasm and most common tumor in horses between 1 and 3 years of age
  • 3 forms include papillomas/papillomatosis (warts) of the skin, genital, and aural plaque
  • Systems affected—skin

Signalment!!navigator!!

  • Any age, but is more common in younger horses (<3 years of age). Congenital papillomas reported in a small number of neonatal foals; however, lack a definitive EcPV isolate
  • No apparent breed or sex predisposition

Signs!!navigator!!

  • Muzzle and lips; however, also found on the eyelids, external genitalia, distal legs, and axilla
  • Lesions may be solitary or multiple (up to 100); can cause problems because of physical location and esthetics
  • Papillomas in any location, except of the ear, are 0.2–2 cm in diameter, 0.5 cm in height, broad-based to pedunculated, gray, pink or white; surface is hyperkeratotic with numerous frond-like projections. Solitary lesions can be larger

Causes and Risk Factors!!navigator!!

  • 7 confirmed EcPVs have been isolated from various lesions and the presence of 1 or more types may occur within a lesion. A putative novel virus has recently been identified
  • EcPV (a DNA papillomavirus)—penetrates stratified squamous or mucosal epithelium via trauma, which may or may not culminate in infection
  • Transmitted by direct and indirect contact (e.g. biting insects, contaminated tack or buckets). Skin barrier breakage is needed for infection to be established
  • Transmission of the virus from the dam to the foal may occur transplacentally (not proven) or inoculation of the skin may occur in the foal from infected sites on the dam during parturition

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

  • The appearance and distribution of the lesions are strongly suggestive of a diagnosis of papillomatosis
  • Verrucose sarcoid (extensive areas are usually affected with markedly thickened skin around and evidence of hypotrichosis at the periphery of the lesion)
  • Squamous cell carcinoma (especially facial, genital, and vulval proliferative forms)

Diagnostic Procedures!!navigator!!

  • Biopsy and histopathologic examination to establish definitive diagnosis
  • Immunohistochemistry to detect viral antigen within the lesion
  • Electron microscopy—while not normally necessary to establish the diagnosis, hexagonal viral particles can be found in all forms of equine papillomatosis (except congenital form)

Treatment ⬆ ⬇

TREATMENT

  • Papillomas (warts) typically regress spontaneously within 1–9 months; therefore, treatment may not be necessary. If lesions persist, look for underlying cause of immunosuppression
  • Surgical excision is the treatment of choice
  • Cryosurgery is also effective
  • Secondary infections may require treatment with topical antibacterial products (e.g. creams, gels, washes)
  • Efficacy of autogenous vaccines is not proved

Medications ⬆ ⬇

MEDICATIONS

  • Generalized papillomatosis—imiquimod 5% cream applied in a thin film to cover the surface of the lesion every 48 h until resolution; alternatively 5% acyclovir (aciclovir) ointment may be an option but no studies have evaluated the efficacy
  • Anecdotal treatment with immunostimulatory agents have been used for persistent papillomatosis and include intralesional injections of interferon alpha or interleukin 2, cisplatin, and bacillus Calmette–Guérin

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Prevention/Avoidance!!navigator!!

  • Papillomaviruses are resistant to freezing or desiccation; however, formalin, detergents, or high temperatures may decrease infectivity
  • Avoid transmission of the virus among horses that are stabled or pastured together by isolation of affected horses and prevention of immunologically susceptible horses from entering the contaminated premise
  • Preventing insect bites (e.g. repellent sprays) may decrease irritation in the affected horse and limit spread of the virus among horses
  • Regular genital sanitation may prevent disease development as poor hygiene has been suggested as a promoter of genital carcinoma or induction of genital papillomatosis

Expected Course and Prognosis!!navigator!!

  • Spontaneous regression of warts is common within 1–9 months
  • Genital papillomas do not spontaneously resolve and may transform into squamous cell carcinoma
  • Surgical excision—excellent prognosis and recurrence should not occur

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Conditions!!navigator!!

Congenital papillomas are a cauliflower-like, flattened wart from 5 mm to 20 cm in diameter on the skin of a new foal. The lesions are usually single and located on the head, neck, or trunk.

Zoonotic Potential!!navigator!!

None

Pregnancy/Fertility/Breeding!!navigator!!

EcPV may be transmitted from an infected mare to the foal transplacentally (not proven) or from infected skin lesions on the mare to the foal during parturition.

Abbreviations!!navigator!!

EcPV = Equus caballus papillomavirus

Author(s) ⬆ ⬇

Author: Gwendolen Lorch

Consulting Editor: Gwendolen Lorch

Acknowledgment: The author/editor acknowledges the prior contribution of Beverly Kidney.

Additional Further Reading ⬆

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