Microbiology & infectious diseases

• 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: Orf Virus (Sore Mouth Infection) [Accessed 10 May 2018])

• 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

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• 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)

• 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

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• 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

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

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

Which of the following diseases is caused by a DNA virus?


1. Hand foot and mouth disease
2. Hepatitis C
3. Measles
4. Orf
5. Rabies

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

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Reference: Orf

Which of the following is true regarding Orf?


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

D. True, inclusion bodies are typically present.

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

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Reference: Orf