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Basics ⬇

Outline

BASICS

Definition!!navigator!!

Any vesicular, ulcerative, or proliferative lesion associated with the penis or preputial folds.

Pathophysiology!!navigator!!

  • The normal surface of the penis is smooth when cleaned of smegma
  • Irregularities in the penile surface or urethral process may be due to infectious, traumatic, inflammatory, or neoplastic lesions
  • Infectious balanitis may be nonspecific bacterial or specific viral (EHV-3) or parasitic (Habronema)
  • EHV-3 is a self-limiting highly contagious venereal disease. Its common name is equine coital exanthema. The incubation period is typically 4–7 days. Lesions are characterized by small raised papules, vesicles, then pustules that later break and form ulcerative lesions that are painful.
    • No proof of a non-clinically apparent carrier state exists, although shedding has been reported to occur immediately prior to vesicle formation
    • As with other herpes infections, virus recrudescence and formation of a new population of vesicles (infective stage) are associated with stress
  • Habronemiasis occurs when larvae of stomach nematodes are deposited on moist mucosal surfaces by stable flies. The larvae cause an influx of eosinophils to the affected tissues, resulting in granulomatous reactions and intense pruritus. Ulceration of the lesions is common
  • The most common neoplasia of the penis and urethral process is SCC. The appearance and progression of the lesions vary

Systems Affected!!navigator!!

Genetics!!navigator!!

N/A

Incidence/Prevalence!!navigator!!

N/A

Geographic Distribution!!navigator!!

Worldwide

Signalment!!navigator!!

Any age and breed can be affected.

Signs!!navigator!!

Historical Findings

  • Poor libido or inability to mate, painful
  • Hemospermia or hematuria

Physical Examination Findings

  • May include visible lesions on the penis, prepuce, urethral process, fossa glandis, and on other mucocutaneous junctions
  • Evidence of a prior EHV-3 infection—healed vesicles leave characteristic lesions on the penis and prepuce consisting of gray (loss of dark pigmentation) irregular patches of penile/preputial skin (many prior vesicles may coalesce into larger patches); affected area of skin remains pliable (interim/inactive phase of EHV-3). Note that there is similar evidence on the vulva of a mare affected by EHV-3
  • Phimosis due to stricture formation, adhesions, or tumor proliferation
  • Paraphimosis due to secondary edema formation or mechanical impedance
  • Hematuria or hemospermia
  • Enlargement of local lymphatics or draining

Causes!!navigator!!

  • Viral infections—EHV-3
  • Parasites—Habronema spp.
  • Neoplasia—SCC, sarcoid, melanoma, papilloma, hemangioma
  • Trauma—chronic wounds, local irritants, thermal injuries
  • Bacteria—abscessation such as that associated with bastard strangles

Risk Factors!!navigator!!

  • Because equine coital exanthema is a venereal disease, natural breeding programs are more likely to have an outbreak than programs using artificial insemination. Similarly, unsanitary breeding practices can put patients at greater risk
  • Unsanitary housing conditions or poor fly control can contribute to Habronemiasis. It is more often seen in hot, humid locations in the spring or summer seasons
  • Gray-colored horses are the most likely to present with melanoma
  • Lightly pigmented horses are more likely to have SCC, and geldings may be affected more than stallions

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

Differentiating Causes

  • EHV-3 infection, typical presentation—multiple, circular, 1–2 mm nodules that progress into vesicles and pustules and ultimately rupture to form ulcerations 5–10 mm in diameter on the penile/preputial mucosa. Systemic involvement is rare, although lesions have been found on other mucocutaneous junctions in some cases
  • Habronemiasis—Bollinger's granules, caseous masses in the exuberant granulation tissue, are diagnostic for habronemiasis. Lesions typically are extremely pruritic. Summer sores, the characteristic lesion, most often occur in the area of the urethral process or on the preputial ring
  • Neoplastic lesions can be either ulcerative or proliferative—SCCs usually are only locally invasive, although they can metastasize to regional lymph nodes and other body tissues
  • Chronic traumatic lesions can mimic any other disease process. Diagnosis is established by history, exclusion, or response to therapy

CBC/Biochemistry/Urinalysis!!navigator!!

N/A

Other Laboratory Tests!!navigator!!

  • Confirmation of EHV-3 by virus isolation from vesicular aspirates
  • Rising antibody titers for EHV-3 from paired sera, at a 14–21 day interval

Imaging!!navigator!!

N/A

Other Diagnostic Procedures!!navigator!!

  • Cytology—intranuclear, eosinophilic inclusion bodies are indicative of EHV-3
  • Biopsy and histopathology can distinguish between the various tumor types and habronemiasis

Pathologic Findings!!navigator!!

N/A

Treatment ⬆ ⬇

Outline

TREATMENT

Appropriate Health Care!!navigator!!

  • Coital exanthema is a self-limiting disease with a course of disease of 3–5 weeks. The lesions can be quite uncomfortable, and secondary bacterial infections can occur. Daily cleansing and the application of emollient or antimicrobial ointments may be indicated. Sexual rest while vesicles form, rupture, and heal prevents venereal transmission
  • Therapy for habronemiasis includes eradicating the infective larvae as well as controlling the local hypersensitivity reaction. Surgical resection of residual scar tissue may be necessary
  • Tumors may be surgically excised, or eliminated with cryosurgery, radiation therapy, hyperthermia, reefing, or phallectomy, dependent upon their size, location, invasiveness, and type
  • Papillomas often regress spontaneously in 3–4 months
  • Topical or intralesional injections of chemotherapeutic agents have been used to address equine sarcoids and penile SCC
  • Chronic wounds should be cleansed, debrided, and closed, when possible. Local irritants (i.e. povidone–iodine scrub) should be thoroughly rinsed off after application, if used
  • Streptococcal infections should be treated with systemic antibiotics

Nursing Care!!navigator!!

See Appropriate Health Care.

Activity!!navigator!!

Depends on the extent of the lesion. Hospitalization may be required.

Diet!!navigator!!

N/A

Client Education!!navigator!!

  • Importance of regular and proper cleaning of the penis and sheath
  • Importance of regular examination of stallions used for breeding to detect early lesions
  • Prebreeding examination and quarantine of mares if natural cover

Surgical Considerations!!navigator!!

Surgical intervention may be the only course of action for some advanced cases of neoplasia.

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

  • Habronema larvae can be eradicated using ivermectin (0.2 mg/kg PO). The use of prednisone to diminish localized pruritic reactions is in question because of questionable gastrointestinal absorption
  • NSAIDs including phenylbutazone (2–4 g/450 kg body weight/day PO) or flunixin meglumine (1 mg/kg/day IV, IM, or PO) are useful for symptomatic treatment of discomfort and to reduce local inflammation
  • Systemic (procaine penicillin G 20 000–22 000 IU/kg IM BID) or local (0.2% nitrofurazone ointment) antibiotics are used to treat primary or secondary bacterial infection

Precautions!!navigator!!

  • Chronic steroid use can result in iatrogenic Cushing disease and may predispose the patient to developing laminitis due to systemic vasoconstrictive action
  • Phenothiazine tranquilizers should be used with caution, or not at all, owing to the possibility of their causing priapism in intact stallions

Possible Interactions!!navigator!!

N/A

Alternative Drugs!!navigator!!

  • Trichlorfon (metrifonate) (22 mg/kg diluted in 1–2 L of 0.9% NaCl slow IV) has been used to eliminate Habronema larvae. There is a risk of clinical organophosphate toxicity
  • Topical application of trichlorfon in 0.2% nitrofurazone (4.5 g trichlorfon in 115 mL (4 oz) of 0.2% nitrofurazone) once daily to granulomatous lesions can be effective in the acute stage of habronemiasis
  • Autogenous vaccines have been suggested to deter the spread of papillomatosis within a herd
  • 5-Fluorouracil in sesame oil has been reported to have some use as a topical sarcoid treatment

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

The frequency of reevaluation depends upon the inciting cause and severity of the lesion.

Prevention/Avoidance!!navigator!!

Avoid breeding activity in the presence of active EHV-3 lesions, but some shedding may occur prior to and immediately after the appearance of vesicles.

Possible Complications!!navigator!!

  • Chronic Habronema spp. infection involving the urethral process can result in periurethral fibrosis; if severe, it will necessitate amputation of the urethral process
  • Paraphimosis
  • Phimosis
  • Metastatic lesions in local lymph, lung, or other body tissues
  • Progression of squamous papillomatous lesions to SCC has been reported
  • Urethral blockage due to either the pathologic condition or therapeutic intervention can occur; urethral patency should be closely monitored

Expected Course and Prognosis!!navigator!!

Prognosis depends on the etiology and extent of lesions.

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

N/A

Associated Conditions!!navigator!!

N/A

Age-Related Factors!!navigator!!

  • Young horses are more likely to present with papillomatous lesions
  • Melanomas are more typically found in aged animals

Zoonotic Potential!!navigator!!

N/A

Pregnancy/Fertility/Breeding!!navigator!!

Coital exanthema does not cause abortion.

Synonyms!!navigator!!

  • EHV-3
  • Equine coital exanthema
  • Equine venereal balanitis
  • Esponja
  • Genital bursatti
  • Genital horse pox
  • Habronemiasis
  • Summer sores
  • Swamp cancer
  • Warts

Abbreviations!!navigator!!

Suggested Reading ⬆ ⬇

Arnold CE, Brinsko SP, Love CC, Varner DD. Use of a modified Vinsot technique for partial phallectomy in 11 standing horses. J Am Vet Med Assoc 2010;237:82–86.

Barrandeguy M, Thiry E. Equine coital exanthema and its potential economic implications for the equine industry. Vet J 2012;191:35–40.

Fortier LA, McHarg MA. Topical use of 5-fluorouracil for treatment of squamous cell carcinoma of the external genitalia of horses: 11 cases (1988–1992). J Am Vet Med Assoc 1994;205:1183–1185.

May KA, Moll HD, Lucroy MD. Recognizing tumors of the equine external genitalia. Compend Contin Educ Pract Vet 2002;24:970–976.

Pugh DG, Hu XP, Blagburn B. Habronemiasis: biology, signs, and diagnosis, and treatment and prevention of the nematodes and vector flies. J Equine Vet Sci 2014;34:241–248.

Van den Top JGB, de Heer N, Klein WR, Ensink JM. Penile and preputial squamous cell carcinoma in the horse: a retrospective study of treatment of 77 affected horses. Equine Vet J 2008;40:533–537.

Author(s) ⬆

Author: Ahmed Tibary

Consulting Editor: Carla L. Carleton

Acknowledgment: The author and editor acknowledge the prior contribution of Carole C. Miller.