Pathology Outlines

Skin inflammatory (nontumor)
Infectious disorders
Orf

Author: Margaret Redpath, M.D.

Senior Author: Ayman Al Habeeb, M.D.

Editorial Board Member: Hillary Rose Elwood, M.D.

Editor-in-Chief: Debra Zynger, M.D.

Topic Completed: 1 April 2018

Revised: 1 April 2019

Copyright: 2003-2019, PathologyOutlines.com, Inc.

PubMed Search: Orf [title] skin

Table of Contents

Cite this page: Redpath M Orf. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/skinnontumororf.html. Accessed June 18th, 2019.

Definition / general

Orf (ecthyma contagiosum) is caused by a double stranded DNA virus of the parapoxvirus genus (Viruses 2015;7:1505)
Primarily a disease of sheep and goats, humans may become infected after direct exposure to the lesions on infected animals (cdc.gov: Orf Virus (Sore Mouth Infection) [Accessed 10 May 2018])

Essential features

Rare viral infection in humans secondary to exposure to infected sheep or goats
Lesions are usually located on forearms and hands
Self-limited course, no treatment is required

Clinical features

Infection typically occurs on fingers, hands and forearms
Lesions typically evolve through several stages:
- Primary macule develops into erythematous papule
- Lesion develops targetoid appearance
- Exudative phase
- Nodule formation
- Drying out and crusting
- Complete regression (JRSM Open 2015;6:2054270415593718)

Clinical images

Images hosted on other servers:

Firm, erythematous papule of the right thumb

Hand infection

Treatment

No specific treatment is required (Johnston: Weedon's Skin Pathology Essentials, 2nd Edition, 2016, cdc.gov: Orf Virus (Sore Mouth Infection) [Accessed 10 May 2018])
Lesions tend to resolve spontaneously within 6 - 7 weeks

Case reports

4 year old girl burn victim (J Infect Dis 2016;214:1171)
16 year old girl with rare human to human transmission (Int J Dermatol 2014;53:e63)
53 year old woman with transmission from cat scratch (Dermatol Online J 2011;17:9)
65 year old woman farmer from Connecticut (Dermatopathology (Basel) 2016;3:55)

Microscopic (histologic) description

Intraepidermal vesiculation (particularly in early lesion)
Epidermal hyperplasia with serum crust, variable epidermal vacuolation
Eosinophilic inclusions in the nucleus or cytoplasm of keratinocytes
Papillary dermal edema with mixed inflammation of lymphocytes, histiocytes, plasma cells
Epidermal necrosis in later lesions

Microscopic (histologic) images

Images hosted on other servers:

Rare necrotic keratinocytes

Legend: balloon degeneration and spongiosis

Diagnosis

Usually based on history of exposure to infected animals with characteristic clinical and histologic features
Electron microscopy and PCR testing can be used to confirm the diagnosis if needed

Electron microscopy description

Intracytoplasmic poxvirus particles
Oval shaped with an electron dense core (Johnston: Weedon's Skin Pathology Essentials, 2nd Edition, 2016)
Laminated capsule

Electron microscopy images

Images hosted on other servers:

Oval viral particles

Differential diagnosis

Anthrax
Cowpox
Herpes simplex
Milker’s nodule
Smallpox
Varicella-Zoster

Board review question #1

Hand foot and mouth disease
Hepatitis C
Measles
Orf
Rabies

Board review answer #1

D. Orf. The other diseases are caused by RNA viruses.

Board review question #2

It is a common viral infection in humans
Direct human to human transmission is the most common mode of transmission
Lesions should be aggressively treated, with surgical resection and antivirals
Cytoplasmic or intranuclear inclusion bodies are usually present within infected keratinocytes
Infected keratinocytic nuclei show margination of chromatin with multinucleation and nuclear molding

Board review answer #2

Incorrect, Orf is a rare viral infection in humans
Incorrect, as transmission is typically from infected sheep or goats to humans, not human to human
Incorrect, lesions typically resolve on their own
Incorrect, answer is describing herpes virus change

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