| Orf | |
|---|---|
| Other names | Contagious pustular dermatitis, contagious ecthyma, infectious labial dermatitis, ecthyma contagiosum, thistle disease, scabby mouth[1] |
 | |
| A thumb with two denuded orf lesions, following a bite by a sheep | |
| Specialty | Infectious diseases,veterinary medicine  |
Orf is afarmyard pox, a type ofzoonosis.[2] It causes smallpustules in theskin of primarilysheep andgoats, but can also occur on the hands of humans.[3] A pale halo forms around a red centre.[4] It may persist for several weeks before crusting and then either resolves or leavesa granuloma.[4] There is usually only one non-painful lesion, but there can be more.[4] Lymph nodes may also become swollen.[4]
It is caused by aparapoxvirus.[5] It can occur in humans who handle infected animals or contaminated objects.[2] One-third of cases may developerythema multiforme.[4] Once resolved, a person can still be infected again.[4]
Generally, once infected, treatment options are limited.[4] Injecting the lesion withcidofovir or applyingimiquimod has been studied.[4] However, it is sometimes required toexcise the pustules.[4] The vaccine used in sheep to prevent orf is live and has been known to cause disease in humans.[4]
The disease is endemic in livestock herds worldwide.[2] A recent outbreak emerged in southwestEthiopia between October 2019 and May 2020.[2]
Orf is also being trialed as a potential and potentviral vector vaccine platform.[6]
Orf is azoonoticdisease, meaning humans can contract this disorder through direct contact with infected sheep and goats or withfomites carrying the orf virus.[7] It causes apurulent-appearingpapule 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 frombestiality). Consequently, it is important to observe good personal hygiene and to wear gloves when treating infected animals.[1] It may appear similar tocowpox andpseudocowpox.[2]
| Orf virus | |
|---|---|
 | |
Virus classification | |
| (unranked): | Virus |
| Realm: | Varidnaviria |
| Kingdom: | Bamfordvirae |
| Phylum: | Nucleocytoviricota |
| Class: | Pokkesviricetes |
| Order: | Chitovirales |
| Family: | Poxviridae |
| Genus: | Parapoxvirus |
| Species: | Parapoxvirus orf |
While orf is usually a benign self-limiting illness which resolves in 3–6 weeks, in theimmunocompromised it can be very progressive and even life-threatening. One percent topicalcidofovir has been successfully used in a few patients with progressive disease. Serious damage may be inflicted on the eye if it is infected by orf, even among otherwise healthy patients. The virus can survive in the soil for at least six months.[8]
Orf is primarily a disease of sheep and goats although it has been reported as a natural disease inhumans,steenbok andalpacas,chamois andtahrs,reindeer,musk oxen,dogs,cats,mountain goats,bighorn sheep,dall sheep, andred squirrels.[8]
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.[8] Orf is spread byfomites and direct contact. In some environments, infection is injected by scratches fromthistles[1] of both growing and felled plants. Symptoms includepapules andpustules on the lips andmuzzle, and less commonly in the mouth of young lambs and on the eyelids, feet, andteats 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 tomastitis.[1] Sheep are prone to reinfection.[9] Occasionally the infection can be extensive and persistent if the animal does not produce an immune response.[1]
A live virusvaccine (ATCvet code:QI04AD01 (WHO)) is made from scab material and usually given to ewes at the age of two months, but typically only given to lambs when there is a confirmed outbreak.[10] The vaccine can cause minor cases of orf when used in humans.[11][12]
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, andaxilla. In rare cases, mostly involving young lambs, lesions are found on the tongue, gums, roof of the mouth and theesophagus. It has also been reported a number of times to cause lesions in therumen. In one case it was shown that a severe form of orf virus caused an outbreak involving thegastrointestinal tract, lungs, heart, as well as thebuccal cavity, cheeks, tongue and lips. Another severe case was reportedpharyngitis, genital lesions and infection of the hooves which led to lameness and, in some cases, sloughing of the hoof.[8]
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.[1]
