Ulcerative dermatosis

E MUNZ AND K DUMBELL

GENERAL INTRODUCTION: POXVIRIDAE

Introduction

Ulcerative dermatosis is an uncommon infectious disease of sheep characterized by multifocal ulceration of the skin of the lips, legs and feet, and the skin and mucous membranes of the genitalia. The disease has been reported from Britain, the USA and South Africa. Generally it is not an economically important disease.¹

Aetiology

The virus that is believed to cause the disease has not been classified but resembles orf virus.^2–4

Epidemiology

All breeds of sheep are affected but mature animals are more commonly affected than younger ones. Mating promotes the occurrence of the genital form, while maintaining sheep on coarse grazing predisposes to the pedal form.

The virus is probably transmitted by direct and indirect contact.

The morbidity rate is usually about 20 per cent, although in the genital form morbidity may reach 80 per cent.¹ Mortality rates are low in sheep in good condition. Secondary bacterial infection may exacerbate the lesions.

Clinical signs and pathology

After an incubation period of about one week, pustules develop predominantly on the lips, face, feet or genitalia. Affected skin and mucous membranes become necrotic and develop into granulating ulcers covered by scabs. Ulcers on the lips, nostrils and other facial areas vary from 5 to 30 mm in diameter, are up to 5 mm in depth, and leave depilated scars after healing. Lesions on the legs are located mostly on the skin covering the metacarpal and metatarsal areas (Figure 112.1) and may cause lameness. The pedal form occurs mostly in free-ranging sheep. In the genital form, ulcers occur on the scrotum (Figure 112.1), glans of the penis, and at the preputial opening of rams and the vulva of ewes. Marked swelling of affected areas occurs in severely affected animals. Phimosis or paraphimosis is common in rams. Scar tissue may replace the glans and urethral process and cause interference during mating.

Diagnosis and differential diagnosis

Ulcerative dermatosis is usually diagnosed by the presence of typical lesions.

The disease can be mistaken for orf, sheeppox, bluetongue, ulcerative balanoposthitis, dermatophilosis, footrot and interdigital abscessation.

Figure 112.1 Ulcerative dermatosis: ulcers on the hind legs and scrotum. (By courtesy of Dr Z. Schenkel, Jordon-German Veterinary Project)

Control

The prevalence of the disease can be reduced by symptomatic treatment of affected animals and by the application of appropriate sanitation and management principles. Affected animals should be isolated. No vaccine is available.

Topical application of antibacterial ointments and sprays is helpful in the control of secondary bacterial infection.

References

1. JENSEN, R. & SWIFT, B.L., 1982. Diseases of Sheep. 2nd edn. Philadelphia: Lea & Febiger.
2. TRUEBLOOD, M.S., 1966. Relationship of ovine contagious ecthyma and ulcerative dermatosis. Cornell Veterinarian, 56, 521–526.
3. TRUEBLOOD, M.S. & CHOW, T.L., 1963. Characterization of the agents of ulcerative dermatosis and contagious ecthyma. American Journal of Veterinary Research, 24, 47–51.
4. TRUEBLOOD, M.S., CHOW, T.L. & GRINER, L.A., 1963. An immunologic study of ulcerative dermatosis and contagious ecthyma. American Journal of Veterinary Research, 24, 42–46.