Orf Virus Infection in Humans: A Review With a Focus on Advances in Diagnosis and Treatment

July 2017 | Volume 16 | Issue 7 | Original Article | 684 | Copyright © 2017

Joseph V. Caravaglio MDa and Amor Khachemoune MD FAAD FACMSb

aCollege of Medicine, University of Central Florida, Orlando, FL bDermatology Service, Veterans Affairs Medical Center and State University of New York, Department of Dermatology, Brooklyn, NY

Abstract

Ecthyma contagiosum, also called contagious pustular dermatosis, is a zoonotic disease caused by the orf virus (OrfV). As a member of the poxviridae family and parapoxvirus genus, this dermatotropic virus has developed an array of mechanisms by which to evade the host immune system in both humans and animals. The ubiquitousness of this pathogen in sheep, goats, and deer has led to the development of orf in diverse areas around the world. Human disease occurs via direct contact with infected animals or fomites. Rarely, human-to-human transmission has been reported. The disease progresses through six clinically distinct dermatologic stages and lesions usually heal in three to six weeks without scarring. Farmers, veterinarians, and hunters represent high-risk groups, as their repeated contact with livestock and wild animals predisposes them to infection. With an increasing number of cattle, livestock, and wild animals being kept as pets, human orf may become more prevalent in the future. Taken with the lack of a widely accepted and successful antiviral treatment regimen, this demonstrates the importance of conducting additional research to further elucidate the pathogenic effects of the OrfV in humans. J Drugs Dermatol. 2017;16(7):684-689.

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INTRODUCTION

As a member of poxviridae, the OrfV belongs to a family of viruses that have had a historically profound impact on human health. Variola, the causative agent of smallpox, is among the most notorious of the poxviruses. Having killed approximately 400,000 people annually in Europe during the latter part of the eighteenth century, the seriousness of this disease was quickly appreciated. Although the origin of this devastating disease is not precisely known, historians believe that it surfaced in humans as far back as 10,000 BC.1 The first physical evidence of the disease was uncovered in 1898 when the mummy of Pharaoh Ramesses V of Egypt was recovered and revealed a facial lesion that is thought to represent smallpox. In fact, it is believed that this deadly viral illness led to his death in 1145 BC. Fortunately, smallpox was eradicated after the advent of the very first effective human vaccine in 1776.2 Though many of the other viruses within the poxviridae family do not pose as significant of a threat to human life as did variola, human infection can increase patient morbidity. The OrfV, for example, causes ecthyma contagiosum which is a relatively benign and self-limiting disease. Humans often become infected after direct exposure to disease-ridden animals. Historically, this disease has been seen with an increased prevalence in people with occupational exposure to animals such as farmers and animal healthcare providers. Over the last two decades in the United States, however, a change in pet demographics has occurred.3 With a rise in the importation of exotic animals and number of livestock being kept as companion animals, OrfV infections may be more pervasive than once thought.3 Clinicians should, therefore, be aware of the clinical manifestations of ecthyma contagiosum so that appropriate treatment and counseling can be provided to affected patients.

Epidemiology and Etiology

Orf has been linked with disease in a variety of animal species. Among those animals, sheep, goats, and cattle are most commonly affected. Strains that affect sheep appear to be distinct from bovine-associated strains, as the nature of cytopathic effects produced differs between the groups.4 More specifically, the parapoxvirus that is associated with ovine infections is the OrfV5,6 whereas cattle are typically infected by the bovine papular stomatitis virus and pseudocowpox virus.7,8,9 Large outbreaks of parapoxvirus infection have also been reported in reindeer over the past two decades, speci cally in northern Europe. When humans become infected with the OrfV via either direct transmission from active lesions on infected animals or through contact with fomites, the condition is referred to as “human orf”.5,10-13 The majority of cases are seen in individuals with occupational exposure to animals such as farmers. Infection is not limited to this group, however, as cases have been reported in shepherds, butchers, slaughter house personnel, animal skin and wool handlers, veterinarians, visitors of petting-zoos, and participants in religious animal sacrifice ceremonies.14-25 Historically, infection in males has outnumbered 

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