Comment
Transmission From Animals to Humans—Orf virus is a member of the Parapoxvirus genus of the Poxviridae family.1 This virus is highly contagious among animals and has been described around the globe. The resulting disease also is known as contagious pustular dermatitis,2 soremuzzle,3 ecthyma contagiosum of sheep,4 and scabby mouth.5 This virus most commonly infects young lambs and manifests as raw to crusty papules, pustules, or vesicles around the mouth and nose of the animal.4 Additional signs include excessive salivation and weight loss or starvation from the inability to suckle because of the lesions.5 Although ecthyma contagiosum infection of sheep and goats has been well known for centuries, human infection was first reported in the literature in 1934.6
Transmission of orf to humans can occur when direct contact with an infected animal exhibiting active lesions occurs.7 Orf virus also can be transmitted through fomites (eg, from knives, wool, buildings, equipment) that previously were in contact with infected animals, making it relevant to ask all farmers about any animals with pustules around the mouth, nose, udders, or other commonly affected areas. Although sanitation efforts are important for prevention, orf virus is hardy, and fomites can remain on surfaces for many months.8 Transmission among animals and from animals to humans frequently occurs; however, human-to-human transmission is less common.9 Ecthyma contagiosum is considered an occupational hazard, with the disease being most prevalent in shepherds, veterinarians, and butchers.1,8 Disease prevalence in these occupations has been reported to be as high as 50%.10 Infections also are seen in patients who attend petting zoos or who slaughter goats and sheep for cultural practices.8
Clinical Characteristics in Humans—The clinical diagnosis of orf is dependent on taking a thorough patient history that includes social, occupational, and religious activities. Development of a nodule or papule on a patient’s hand with recent exposure to fomites or direct contact with a goat or sheep up to 1 week prior is extremely suggestive of an orf virus infection.
Clinically, orf most often begins as an individual papule or nodule on the dorsal surface of the patient’s finger or hand and ranges from completely asymptomatic to pruritic or even painful.1,8 Depending on how the infection was inoculated, lesions can vary in size and number. Other sites that have been reported less frequently include the genitals, legs, axillae, and head.11,12 Lesions are roughly 1 cm in diameter but can vary in size. Ecthyma contagiosum is not a static disease but changes in appearance over the course of infection. Typically, lesions will appear 3 to 7 days after inoculation with the orf virus and will self-resolve 6 to 8 weeks later.
Orf lesions have been described to progress through 6 distinct phases before resolving: maculopapular (erythematous macule or papule forms), targetoid (formation of a necrotic center with red outer halo), acute (lesion begins to weep), regenerative (lesion becomes dry), papilloma (dry crust becomes papillomatous), and regression (skin returns to normal appearance).1,8,9 Each phase of ecthyma contagiosum is unique and will last up to 1 week before progressing. Because of this prolonged clinical course, patients can present at any stage.
Reports of systemic symptoms are uncommon but can include lymphadenopathy, fever, and malaise.13 Although the disease course in immunocompetent individuals is quite mild, immunocompromised patients may experience persistent orf lesions that are painful and can be much larger, with reports of several centimeters in diameter.14
Dermatopathology and Molecular Studies—When a clinical diagnosis is not possible, biopsy or molecular studies can be helpful.8 Histopathology can vary depending on the phase of the lesion. Early stages are characterized by spongiform degeneration of the epidermis with variable vesiculation of the superficial epidermis and eosinophilic cytoplasmic inclusion bodies of keratinocytes (Figure 3). Later stages demonstrate full-thickness necrosis with epidermal balloon degeneration and dense inflammation of the dermis with edema and extravasated erythrocytes from dilated blood vessels. Both early- and late-stage disease commonly show characteristic elongated thin rete ridges.8
FIGURE 3. A, Hyperplastic follicles with balloon cell change, perinuclear vacuolization, and surrounding acute and chronic dermatitis (H&E, original magnification ×40). B, Perinuclear vacuolization (green arrows) with eosinophilic viral cytoplasmic inclusion bodies (black arrows) and nuclear pseudoinclusion bodies (black circles)(H&E, original magnification ×400).