Rapidly growing cutaneous nodules in a sheep worker

A healthy 22-year-old male, presented with two tender nodules on his right middle finger and right forearm. They had appeared five days earlier as erythematous macules and were growing rapidly. Examination revealed two ulcerated nodules (Figure 1). He was afebrile and systemic symptoms were absent. A biopsy revealed focal necrosis of the epidermis with neutrophils and an extensive lymphohistiocytic infiltrate in the dermis with some red intracytoplasmic inclusions (Figure 2). CD30 stain revealed infiltration by reactive lymphocytes (Figure 3). Microbiological cultures from biopsy for bacterial, mycobacterial and fungi and PCR for leishmaniasis were negative. Suspecting an infection, we asked him about his occupation. He milked sheep mechanically.

Figure 1.

A 2-cm diameter erythematous and exophytic nodule with ulceration on his right middle finger, with surrounding edema. Another 0.8-cm ulcerated nodule is present on his forearm.

Figure 2.

Cutaneous biopsy (from finger) reveals large intracytoplasmic eosinophilic inclusions within the keratinocytes in some cells (arrows) (Hematoxylin-eosin stain, ×400).

Figure 3.

Marked reactive lymphoid infiltrate with CD30 positive T cells (arrows) (CD 30 stain, ×200).

Answer: Orf virus infection

Contagious ecthyma, also known as Orf nodule or disease in humans, is a viral zoonotic disease.¹ It primarily occurs in sheep and goats worldwide, as exudative lesions typically located in the oral region, nostrils, eyelids, udder and teats. Humans, especially persons exposed in the workplace, are infected through direct contact with animals or contaminated fomites. After an incubation period of 3-8 days, orf progresses through six stages: initially a small erythematous macule appears that transforms into a papule, which progresses continuously into a nodular, and often vesicular, targeted lesion. The nodule ulcerates and resolves spontaneously within 3-6 weeks. Constitutional symptoms, lymphadenopathy, superinfection and immune hypersensitivity reactions are uncommon.^1-4

Microscopically, the parapoxvirus infection is characterized by the presence of eosinophilic inclusion bodies in the cytoplasm of vacuolated epidermal cells in the upper epidermis. A marked reactive lymphoid infiltrate with CD30 positive T cells may be present.⁴ Electron microscopy reveals numerous viral particles and PCR can definitively identify orf virus.^1,3 However, in general, the diagnosis of Orf disease is based on the history, physical examination and clinical evolution of the patient.

Differential diagnoses include rapidly growing cutaneous tumors in fingers and hands, as pyogenic granuloma, keratoacanthoma, nodular melanoma, cutaneous lymphoma, Merkel cell carcinoma and cutaneous metastasis. Moreover, various cutaneous infections (cutaneous anthrax, tularemia, erysipeloid, sporotrichosis, leishmaniasis and atypical mycobacterial infections) may have a similar presentation. Milker's nodules have identical clinical manifestations and histopathology. However, the epidemiological context is different as milker's nodules is caused by a bovine origin parapoxvirus, while orf is of caprinic origin parapoxvirus.

Orf does not require specific treatment, because it shows spontaneous regression within 4–8 weeks. Nevertheless, local antiseptic treatment is recommended to prevent bacterial super-infection. Diagnosis of orf disease is mostly based on the history of animal contact and clinical findings in a patient with single or multiple erythematous nodules growing rapidly on the fingers.

Funding Statement

None.