Background
Orf (also known as ecthyma contagiosum, contagious pustular dermatitis, infectious labial dermatitis, scabby mouth, or sore mouth) is a viral disease first described in humans in 1934 by Newsom and Cross. [1] The orf virus is endemic in sheep and goat herds worldwide and occurs rarely in cattle, camels, and other ruminants. [2]
Orf causes skin lesions on the lips, muzzle, ears, eyelids, and nostrils of infected animals, and less commonly on the genitalia, udders, and feet. [3] The virus is transmitted to humans through direct contact with an infected animal or, less commonly, contaminated fomites. Although human-to-human transmission is extremely rare, it has been reported. [4] Lesions occur most commonly on the hands (see the image below) and can serve as a source of autoinoculation when patients scratch or touch breaks in their skin elsewhere on the body. [5]
Orf is frequently seen in ranching communities, veterinarians, and those who process animals for consumption. [6, 7] Orf has been reported in people who prepare sheep or goats for religious feasts. The most common association is with the Muslim practice of Eid ul-Adha, but cases have been reported in Jewish Passover and Christian Easter celebrations. [8, 9, 10, 11, 12] There have been reports of orf in children who were exposed to animals on farms and petting zoos. [13]
Orf typically has a self-limited course, with spontaneous resolution occurring within 4-8 weeks after progressing through six distinct stages (see Presentation). [14] Recurrences due to repeat infection may occur, but they generally result in lesions that are less pronounced than the primary infection.
Pathophysiology
Orf is caused by infection with the orf virus that belongs to the Parapoxvirus genus, which also includes bovine papular stomatitis virus, pseudocowpoxvirus, red deerpox virus, and grey sealpox virus. [15] Parapoxvirus is a member of the family Poxviridae, which are double-stranded DNA viruses. [16]
The orf virus is a cylindrical virus measuring 260 × 160 nm. Its surface tubules form a long crisscross pattern that is seen on negatively stained preparations by electron microscopy. This virus resists physical damage and persists through the winter months on hedges, feeding troughs, fences, harnesses, and barns. [17] It can remain viable on the wool of animals and on items that remain at room temperature for years. [18, 19]
The orf virus is able to produce a homolog of the anti-inflammatory cytokine interleukin (IL)-10, which contributes to localized suppression of immunity. [20, 21] Orf virus also produces an inhibitory protein that blocks both IL-2 and granulocyte-macrophage colony-stimulating factor (GM-CSF), as well as a vascular endothelial growth factor (VEGF) homolog that promotes angiogenesis. [22] The B2L major envelope protein has lipase activity and immunomodulating properties. [23]
Orf is transmitted by direct contact inoculation, usually via a wound in the skin. Humans acquire the infection from contact with infected animals, carcasses, or contaminated nonliving fomites. Orf is most commonly contracted by shepherds, veterinary surgeons, and farm workers who bottle-feed young lambs, as well as by butchers, cooks, and meat porters who handle infected carcasses. It has been linked to exposures at petting zoos, religious meals, and livestock shows. [24]
Autoinoculation to the genital area and face can occur, but human-to-human transmission is rare, and only a few possible cases have been reported in the literature. [17, 25, 26, 27, 4] Nosocomial human-to-human transmission was reported in patients on a burn unit. [28]
Epidemiology
The majority of orf infections go unreported, both because the disease is self-limited and because those infected often recognize the condition and do not seek medical attention.
Orf is an occupational hazard for ranchers, veterinarians, butchers, shearers, and shepherds. It has been reported in people who prepare sheep or goats for religious feasts—most commonly with the Muslim practice of Eid ul-Adha but also in Jewish Passover and Christian Easter celebrations. [8, 9, 10, 11, 12]
Lesions are more common in adults but have been reported in children as young as 4 months after exposure to animals on farms and petting zoos. [13, 29] Orf occurs more commonly in men because men are more likely to have an occupational exposure (eg, from ranching, veterinary medicine, or animal slaughter). [13] No racial predilection exists.
Prognosis
The prognosis for patients with orf is excellent. Lesions in immunocompetent hosts usually heal completely without scarring in approximately 35 days (4-8 wk). Scarring may occur if secondary infection or trauma to the lesion develops.
Complications such as erythema multiforme, bullous pemphigoid, swan-neck deformity, paresthesia, and autoimmune vesicular disorders, though rare, have been reported. [1, 30]
In immunocompromised patients, orf can present with progressive, destructive lesions that are more persistent, resist treatment, and are more likely to recur. These cases may require medical interventions, including antiviral therapy, reduction of immunosuppression, and surgical debridement. [31, 32]
Mortality from orf infection has not been reported in the medical literature.
Patient Education
Most patients infected with orf are farmers or people who handle animals; accordingly, they usually are already familiar with the disease. patients who are unacquainted with this condition should be reassured that the disease typically runs a benign, self-limited course, and they should be instructed on proper wound care. Patients should also be informed that recurrences due to repeat infection may occur but that they generally result in lesions that are less pronounced than those from the primary infection. The best treatment is prevention with the use of gloves and strict hand hygiene.
Further information on orf infections in both humans and animals is available at the US Centers for Disease Control and Prevention (CDC) website. [33]
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Orf, stage 1 (maculopapular).
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Classic location of orf on index finger.
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Orf, stage 2 (targetoid). Bulla with irislike configuration.
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Orf, stage 4 (regenerative). Firm nodule with central crust.
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Orf lesion (arrow) associated with erythema multiforme.
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Orf, stage 3 (acute). Weeping nodule. Image from Thompson HJ et al. Cutis. 2022 Jul. 110 (1):48-52.
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Upper image: Hyperplastic follicles with balloon cell change, perinuclear vacuolization, and surrounding acute and chronic dermatitis (H&E, original magnification ×40). Lower image: Perinuclear vacuolization (green arrows) with eosinophilic viral cytoplasmic inclusion bodies (black arrows) and nuclear pseudoinclusion bodies (black circles) (H&E, original magnification ×400). Image from Thompson HJ et al. Cutis. 2022 Jul. 110 (1):48-52.
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(A) Orf on right thumb relapsing after surgical excision. (B) Lesion continued to grow after 6 weeks of therapy with oral valacyclovir and imiquimod cream 5%. (C) Change of treatment to SC injections of interferon alfa-2a along with imiquimod cream 5% resulted in resolution after 9 weeks. Image from Ertekin SS et al. Cutis. 2017 May. 99 (5):E19-E21.
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