Answer: Orf virus infection

Abstract

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][2][3][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.