Orf

Also known as Contagious Pustular Dermatitis, Contagious Ecthyma and Scabby Mouth, Orf is the most common viral zoonosis in the UK.

Contagious ecthyma (Courtesy of Bristol BioMed Image Archive)

The virus is a large, enveloped, highly epitheliotropic, DNA virus which is ovoid in shape and measures 220‑300 x 140‑170 nm
There are over 100 polypeptides in the virion
The core proteins include a transcriptase and several other enzymes
The virus is immunologically related to those causing bovine papular stomatitis, pseudocowpox, sealpox, deer PPV, red squirrel PPV and camel PPV
There is extensive cross‑neutralization and cross‑protection between viruses belonging to the same genus, but not between those of different genera
The virus is resistant to desiccation

Acute debilitating but rarely fatal skin disease of sheep, goats and incidentally of ruminants and humans

Trauma, then lesions on skin without wool
Lesions on udder and throat and in mouth
Lesions coalesce to form scabbed masses
Particular concern for lambs, who stop feeding due to mouth lesions
For more, see here
In man, papules and pustules develop on hands within 10 days, enlarge and then regress after several weeks

Morbidity may reach 90%, but mortality rarely exceeds 1%, unless secondary infection or myiasis occurs
The course of the disease without complications is 2‑6 weeks, and it takes about 10 weeks to run a course through a naive flock, but often lingers indefinitely in the flock because it can reinfect the same animal many times and is resistant to desiccation

Sheep pox: A more severe disease
- Characterized by elevated papules distributed diffusely over the skin surface
- Inclusion bodies are often seen, but there is no down‑growth of epidermis
- High mortality
Ulcerative dermatosis:
- Characterized by ulcers and crusts on the skin of the face, feet and genitalia
- The lesions are not elevated because there is no epithelial hyperplasia
Bluetongue Virus:
- There is a lower morbidity but a high mortality
- The disease is usually seen in adult animals
- This is a severe systemic disease which is a differential only for the rare, systemic form of CE
Mycotic dermatitis:
- The scabs are smaller and thinner and lighter and usually yellowish in color, with crusts not firmly attached
Foot and mouth disease: When lesions occur in the mouth

In sheep produces a proliferative nodule/papular mass on lips
In flocks in which it is endemic it is seen in lamb
If flock is non-immune seen in ewes too but much worse in lambs (may spread to inside of mouth)
Can spread to udder of ewe

Papular proliferative pathology

Poxvirus infections produce local infection of prickle cells in epithelium with proliferation of cells and formation of papule followed by ulceration / necrosis and covered by necrotic epithelium
Eventually scabs form and crust drops off
Scabs - very infectious ( N.B.if touch -> catch it)

Attenuated virus can be applied by scarification to axillar, causing scabs to fall off in 30 days
Annual vaccination of ewes at least 8 weeks before lambing (all in contact should be done simultaneously)
In an outbreak, all lambs can be vaccinated

From pathology

Also called contagious pustular dermatitis, orf, sore mouth
Caused by a parapox virus
Affects mainly young sheep, less commonly cattle, humans, dogs
Starts in abrasions around mouth commisures and spreads to lips, oral mucosa, eyelids and feet
May also transfer to teats of the mother of an affected lamb
Lesions typical of poxvirus but very brief vesicle stage
Most obvious is the proliferative pustular stage