• Author: Luke Bloomquist, MD; Chief Editor: Mark R Wallace, MD, FACP, FIDSA  more...
Updated: Oct 07, 2015


Poxviridae are a family of oval or brick-shaped, quite large, double-stranded DNA viruses that can infect both humans and animals. The genus Parapoxvirus is included among these viruses; these viruses measure 260 X 160-nm and possess a unique spiral coat that distinguishes them from the other poxviruses. Parapoxvirus species are enzootic to hoofed animals (ungulates) throughout the world. Three similar parapoxviruses (orf virus, pseudocowpox virus, and bovine papular stomatitis virus) commonly cause infection in humans; transmission is through direct or indirect contact with infected animals. The zoonotic hosts of these parapoxviruses are sheep and goats (orf, ie, ecthyma contagiosum virus) and cattle (pseudocowpox virus [ie, milker's nodule virus or paravaccinia virus] and bovine papular stomatitis virus).

Other parapoxviruses have been recognized in New Zealand red deer,[1] Finnish reindeer,[2] Japanese serows,[3] European musk oxen,[4] red squirrels in the United Kingdom,[5] harbor seals in the North Sea,[6] and California sea lions.[7] A novel parapoxvirus from white-tailed deer in the United States has caused cases of human infection.[8]

Parapoxvirus infections manifest as pathologic lesions on the animal's oral mucosa (eg, lips, nostrils, eyes) or the moist hairless areas of the skin (eg, udders, groin). The virus may be contacted even in the absence of obvious lesions on the animal.[9]

Incidence of deer-associated parapoxvirus infections may rise as the deer population in the United States continues to increase.[8]

Clinical cutaneous manifestations of infection with the parapoxviruses are identical; therefore, some authors propose the term "farmyard pox" for any of the 3 common parapoxvirus infections.[10]

Go to Poxviruses, Orf, and Milker's Nodules for complete information on these topics. 



Parapoxvirus infection results in solitary or multiple, relatively painless, cutaneous lesions that heal slowly, usually without complications. Occasionally, the lymphatic system is involved. Even in immunocompromised hosts, little evidence suggests spread of infection outside external surfaces.

Lasting immunity to parapoxviruses does not seem to occur, and reinfection has been reported.[11]




United States

Orf, milker's nodule, and bovine papular stomatitis are viral illnesses enzootic to sheep, goats, and cattle throughout the world. No reports contain data specific to the United States.


Data from England and Wales for 1990-1995 indicate an annual mean of 15 human cases of parapoxvirus infections, significantly less than the reported annual mean of 46 cases between 1978 and 1986. Sheep were a more frequent source of infection than other ungulates.[12]

Among high-risk populations, such as animal caretakers or meat handlers,[13] the typical clinical appearance and the benign nature of the infection may be well known. As a result, infected individuals may not seek medical attention and many authors believe that the infection is much more common than actually reported.


Parapoxvirus lesions generally heal without treatment, albeit slowly. Scarring is typically absent. Immunocompromised patients and those with atopic dermatitis are at risk for progressive or disseminated disease. One case reported described blindness resulting from ocular involvement; no cases resulting in death have been reported.[14]


Race is often not specified in the existing literature, but the infection occurs throughout the world.


Most cases occur in males, reflecting the male predominance in the occupations or activities of the infected patients, which include veterinarians, veterinary students, farmers, shepherds, and other animal caretakers. Women are susceptible to infection if they have close contact with animals.


Most cases occur in young to middle-aged adults, although school-aged children also are infected. Parapoxviruses do not appear to have a predilection for any particular age group. Children may be at higher risk due to behavioral reasons that cause them to sustain more animal bites, to have poorer adherence to good hand hygiene and personal protective measures, and to engage in high-risk behaviors such as nuzzling a sick animal.[15] A recent analysis of an orf outbreak found that age less than 20 years was an independent risk factor for infection.[16]

Contributor Information and Disclosures

Luke Bloomquist, MD Combat Aviation Brigade Surgeon, 1st Armored Division, Fort Bliss, Texas

Luke Bloomquist, MD is a member of the following medical societies: American Academy of Family Physicians, Society of US Army Flight Surgeons

Disclosure: Nothing to disclose.


Gary P Holmes, MD FSHEA, FIDSA, Joint Professor, Department of Epidemiology and Biostatistics, Texas A&M University School of Rural Public Health

Gary P Holmes, MD is a member of the following medical societies: American Society for Microbiology, Infectious Diseases Society of America, Society for Healthcare Epidemiology of America, Armed Forces Infectious Diseases Society

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Thomas M Kerkering, MD Chief of Infectious Diseases, Virginia Tech Carilion School of Medicine

Thomas M Kerkering, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Physicians, American Public Health Association, American Society for Microbiology, American Society of Tropical Medicine and Hygiene, Infectious Diseases Society of America, Medical Society of Virginia, Wilderness Medical Society

Disclosure: Nothing to disclose.

Chief Editor

Mark R Wallace, MD, FACP, FIDSA Clinical Professor of Medicine, Florida State University College of Medicine; Clinical Professor of Medicine, University of Central Florida College of Medicine

Mark R Wallace, MD, FACP, FIDSA is a member of the following medical societies: American College of Physicians, American Medical Association, American Society for Microbiology, Infectious Diseases Society of America, International AIDS Society, Florida Infectious Diseases Society

Disclosure: Nothing to disclose.

Additional Contributors

Pranatharthi Haran Chandrasekar, MBBS, MD Professor, Chief of Infectious Disease, Program Director of Infectious Disease Fellowship, Department of Internal Medicine, Wayne State University School of Medicine

Pranatharthi Haran Chandrasekar, MBBS, MD is a member of the following medical societies: American College of Physicians, American Society for Microbiology, International Immunocompromised Host Society, Infectious Diseases Society of America

Disclosure: Nothing to disclose.


The authors and editors of Medscape Reference gratefully acknowledge the contributions of previous authors Larry I Lutwick, MD, and Adam M Rotunda, MD, to the development and writing of this article.

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