Orf Virus in Humans: Case Series and Clinical Review
Ecthyma contagiosum (orf), a worldwide cause of the hand pustule, is caused by orf virus, a member of the genus Parapoxvirus, which causes an epitheliotropic zoonotic infection that spreads from ruminants (even-toed ungulate mammals such as sheep or goats) to humans. Similar members within the poxvirus family can cause a clinically identical viral pustule, which is spread to humans from the respective animal host reservoirs. These entities are impossible to clinically differentiate in the absence of social history or specific polymerase chain reaction studies, though their frequency does vary based on location across the globe.
Although its 1-cm solitary hand pustule often is easily diagnosed by the experienced dermatologist, the goal of this review is to expand the understanding of the presentation, differential diagnosis, and treatment of this condition. We present 5 clinical cases of orf. Special care also has been taken to expand on our report of the unique associated cultural and social elements that the expert diagnostician should obtain to determine etiology.
Early and rapid diagnosis of this classic condition are critical to prevent unnecessary biopsies or extensive testing, and determination of etiology can be important to prevent reinfection or spread to other humans by the same infected animal.
Practice Points
- Ecthyma contagiosum is a discrete clinical entity that occurs worldwide and demands careful attention to clinical course and social history.
- Ecthyma contagiosum is caused by orf virus, an epitheliotropic zoonotic infection that spreads from ruminants to humans.
- Early and rapid diagnosis of this classic condition is critical to prevent unnecessary biopsies or extensive testing, and determination of etiology can be important in preventing reinfection or spread to other humans by the same infected animal.
Molecular studies are another reliable method for diagnosis, though these are not always readily available. Polymerase chain reaction can be used for sensitive and rapid diagnosis.15 Less commonly, electron microscopy, Western blot, or enzyme-linked immunosorbent assays are used.16 Laboratory studies, such as complete blood cell count with differential, erythrocyte sedimentation rate, and C-reactive protein, often are unnecessary but may be helpful in ruling out other infectious causes. Tissue culture can be considered if bacterial, fungal, or acid-fast bacilli are in the differential; however, no growth will be seen in the case of orf viral infection.
Differential Diagnosis—The differential diagnosis for patients presenting with a large pustule on the hand or fingers can depend on geographic location, as the potential etiology may vary widely around the world. Several zoonotic viral infections other than orf can present with pustular lesions on the hands (Table).17-24
Clinically, infection with these named viruses can be hard to distinguish; however, appropriate social history or polymerase chain reaction can be obtained to differentiate them. Other infectious entities include herpetic whitlow, giant molluscum, and anthrax (eTable).24-26 Biopsy of the lesion with bacterial tissue culture may lead to definitive diagnosis.26
Treatment—Because of the self-resolving nature of orf, treatment usually is not needed in immunocompetent patients with a solitary lesion. However, wound care is essential to prevent secondary infections of the lesion. If secondarily infected, topical or oral antibiotics may be prescribed. Immunocompromised individuals are at increased risk for developing large persistent lesions and sometimes require intervention for successful treatment. Several successful treatment methods have been described and include intralesional interferon injections, electrocautery, topical imiquimod, topical cidofovir, and cryotherapy.8,14,27-30 Infections that continue to be refractory to less-invasive treatment can be considered for wide local excision; however, recurrence is possible.8 Vaccinations are available for animals to prevent the spread of infection in the flock, but there are no formulations of vaccines for human use. Prevention of spread to humans can be done through animal vaccination, careful handling of animal products while wearing nonporous gloves, and proper sanitation techniques.
Complications—Orf has an excellent long-term prognosis in immunocompetent patients, as the virus is epitheliotropic, and inoculation does not lead to viremia.2 Although lesions typically are asymptomatic in most patients, complications can occur, especially in immunosuppressed individuals. These complications include systemic symptoms, giant persistent lesions prone to infection or scarring, erysipelas, lymphadenitis, and erythema multiforme.8,31 Common systemic symptoms of ecthyma contagiosum include fever, fatigue, and myalgia. Lymphadenitis can occur along with local swelling and lymphatic streaking. Although erythema multiforme is a rare complication occurring after initial ecthyma contagiosum infection, this hypersensitivity reaction is postulated to be in response to the immunologic clearing of the orf virus.32,33 Patients receiving systemic immunosuppressive medications are at an increased risk of developing complications from infection and may even be required to pause systemic treatment for complete resolution of orf lesions.34 Other cutaneous diseases that decrease the skin’s barrier protection, such as bullous pemphigoid or eczema, also can place patients at an increased risk for complications.35 Although human-to-human orf virus transmission is exceptionally rare, there is a case report of this phenomenon in immunosuppressed patients residing in a burn unit.36 Transplant recipients on immunosuppressive medications also can experience orf lesions with exaggerated presentations that continue to grow up to several centimeters in diameter.31 Long-term prognosis is still good in these patients with appropriate disease recognition and treatment. Reinfection is not uncommon with repeated exposure to the source, but lesions are less severe and resolve faster than with initial infection.1,8
Conclusion
The contagious hand pustule caused by orf virus is a distinct clinical entity that is prevalent worldwide and requires thorough evaluation of the clinical course of the lesion and the patient’s social history. Several zoonotic viral infections have been implicated in this presentation. Although biopsy and molecular studies can be helpful, the expert diagnostician can make a clinical diagnosis with careful attention to social history, geographic location, and cultural practices.
