|Other names: Contagious pustular dermatitis, contagious ecthyma, infectious labial dermatitis, ecthyma contagiosum, thistle disease, scabby mouth|
|A thumb with two denuded orf lesions, following a bite by a sheep|
|Symptoms||Single small pus filled bump|
|Usual onset||1 wk after exposure|
|Duration||Less than 8 wks|
|Causes||Orf virus (ORFV)|
|Risk factors||Handling affected sheep and goats|
|Differential diagnosis||Ecthyma gangrenosum, vaccinia, anthrax, erysipeloid, tularemia|
|Frequency||Relatively common in at risk groups|
Orf is a viral infection, acquired from other animals. Symptoms are a pus filled bumps of the skin a few centimeters in size; generally, of the hands or forearms. A pale halo may forms around the red center and than crust over. Onset is about a week after exposure and generally a single lesion occurs. Pain, slight fever, or swollen lymph glands may occur. A few cases are associated with erythema multiforme.
It is caused by the Orf virus (ORFV), a type of Parapoxvirus. It generally spreads to people by infected sheep, particularly lambs, or goats. Rarely cases may occur from contaminated objects or other people. People who work with animals are most commonly affected. Once resolved, a person can be infected again. Diagnosis may be supported by PCR. It is a type of is a farmyard pox, together with milker's nodule.
Generally, no specific treatment is required. Occasionally cidofovir or imiquimod is used. It is rarely necessary to cut them out. The vaccine used to prevent disease in sheep is live and can cause disease in humans. Generally the lesion resolves within 8 weeks.
The disease is relatively common in areas with goat or sheep farming. Livestock herds are more commonly affected than people. It became more common in southwest Ethiopia between October 2019 and May 2020. The disease was officially described in 1787, though had been known previously. Other animals commonly develop facial lesions.
Signs and symptoms
Symptoms include a purulent-appearing papule locally and generally no systemic symptoms. Infected locations can include the finger, hand, arm, face and even the penis (caused by infection either from contact with the hand during urination or from bestiality).
While orf is usually a benign self-limiting illness which resolves in 3-6 weeks, in the immunocompromised, it can be progressive and even life-threatening. Serious damage may occur in the eye if it is infected by orf, even among healthy individuals.
The virus can survive in the soil for at least six months.
It is important to observe good personal hygiene and to wear gloves when treating infected animals.
One percent topical cidofovir has been successfully used in a few people with progressive disease.
Orf is primarily a disease of sheep and goats although it has been reported as a natural disease in humans, steenbok and alpacas, chamois and tahrs, reindeer, musk oxen, dogs, cats, mountain goats, bighorn sheep, dall sheep, and red squirrels.
Sheep and goats
It has been recorded since the late 19th century and has been reported from most sheep-or goat-raising areas, including those in Europe, the Middle East, the United States, Africa, Asia, South America, Canada, New Zealand and Australia. Orf is spread by fomites and direct contact. In some environments, infection is injected by scratches from thistles of both growing and felled plants. Symptoms include papules and pustules on the lips and muzzle, and less commonly in the mouth of young lambs and on the eyelids, feet, and teats of ewes. The lesions progress to thick crusts which may bleed. Orf in the mouths of lambs may prevent suckling and cause weight loss, and can infect the udder of the mother ewe, thus potentially leading to mastitis. Sheep are prone to reinfection. Occasionally the infection can be extensive and persistent if the animal does not produce an immune response.
A live virus vaccine (ATCvet code: QI04AD01 (WHO)) is made from scab material and usually given to ewes at the age of two months, but only to lambs when there is an outbreak. The vaccine can cause disease in humans.
In sheep and goats, the lesions mostly appear on or near the hairline and elsewhere on the lips and muzzle. In some cases the lesions appear on and in the nostrils, around the eyes, on the thigh, coronet, vulva, udder, and axilla. In rare cases, mostly involving young lambs, lesions are found on the tongue, gums, roof of the mouth and the oesophagus. It has also been reported a number of times to cause lesions in the rumen. In one case it was shown that a severe form of orf virus caused an outbreak involving the gastrointestinal tract, lungs, heart, as well as the buccal cavity, cheeks, tongue and lips. Another severe case was reported pharyngitis, genital lesions and infection of the hooves which led to lameness and, in some cases, sloughing of the hoof.
More typically, sheep will become free of orf within a week or so as the disease runs its course. Sheep custodians can assist by ensuring infected lambs receive sufficient milk and separating out the infected stock to slow down cross-transmission to healthy animals. It is advisable for those handling infected animals to wear disposable gloves to prevent cross infection and self-infection. A veterinarian must be contacted if there is a risk of misdiagnosis with other, more serious conditions.
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