Orf is also known as Contagious Pustular Dermatitis, Contagious Ecthyma
The orf virus is classified as a Poxvirus belonging to the genus Parapoxvirus. Orf is a pathogen found worldwide and causes significant losses in livestock production for sheep farmers. It is also unfortunately a zoonotic disease, which means humans can contract the virus from the sheep. So farmers have to take a lot more care to prevent contracting the virus themselves if it gets in the flock.
Spring is the most likely time for an orf outbreak and in young lambs in the first year of their life.
The orf virus is a very painful skin condition causing scabby lesions around the nose, inside and outside of their mouths, their feet and sometimes other parts of the body. The primary affected area is around the mouth and in usual circumstances the orf virus can be eradicated in 4 to 6 weeks.
If however the lesions have become more extensive and spread which can even affect the udder which will cause the ewe to deny suckling due to the soreness of the infection.
If the ewe has lesions on her udders there is a high risk of developing acute staphylococcal which is mastitis in ewes. If this is the case she will refuse to let her lamb suckle and the lamb will starve. There is also a risk of the lambs spreading to other ewes whilst trying to suckle them.
How orf spreads
The orf virus spreads through the flock from direct contact with a contaminated animal but is also spread through any items that have come into contact with the infected sheep, such as, clothing, items used on the sheep, it can also be spread from fence posts or such that an infected animal has rubbed against.
Orphaned lambs are particularly prone to orf, this could be because of lower immunity without the mother’s colostrum or a higher risk from the feeding equipment used in place of the ewe. Insects that bite are also believed to carry and spread the virus.
Orf spreads through the flock incredibly rapidly especially for housed sheep or in sheep that have been transported to a different location, as the virus can contaminate the livestock trailers. Once orf has got hold most animals in the flock will develop symptoms within a few weeks. Outbreaks typically last for around 6 – 8 weeks without a renewed threat until the next batch of lambs are born.
Lambs that have contracted orf
Lambs that have contracted an acute bout of orf are often unable to eat for extensive periods of time, even days because of the lesions make eating so painful for them. This of course both causes weight loss and a lowered immunity which leaves the lambs vulnerable to picking up a secondary bacterial infection from the lesions. This leaves them at further risk of prolonged disease and a risk of mortality.
The orf virus can remain on contaminated materials such as fencing, lambing sheds and in the sheep’s wool, and skin for years in dry, cool environments. Studies discovered the orf virus had remained effective for 17 years in a dry climate. Cold, wet environments do diminish the infectivity of orf though.
Sheep that have contracted orf don’t build up an immunity to prevent further outbreaks but subsequent infections do appear to be milder and for less long.
For flocks that have never had the virus, to retain your orf free status, be careful when buying in new ewes or rams that they are from orf free farms. When new sheep are bought in they should first be isolated from your existing flock and carefully examined for any signs of orf.
Pasture management is also a core prevention factor with orf, any thistles on your land need to be removed and a tight control maintained as thistles can traumatise the skin allowing the orf virus to infect the sheep. Vaccinations for orf are only for managing the condition in infected sheep and lambs and is not to be used for uninfected sheep.
How to deal with an orf outbreak
If you have an outbreak in your sheep, as orf is a virus most treatment doesn’t have much effect. Antibiotics are only useful or indeed effective at treating secondary bacterial infections that occur on the scabbed skin caused by orf, and probably partly to the animals lowered immunity due to the condition and it’s inability to eat properly due to the soreness of their mouths.
Orf is self-limiting so if you are able to successfully prevent secondary bacterial infections, the virus should clear up in 24 to 48 days.
Isolate animals infected with orf
Any animals infected with orf need to be isolated from the rest of the flock, indoors ideally and as soon as possible to prevent orf spreading. Ensure lots of bedding to reduce the risk of uninfected animals having contact with scabs in the shed.
Treating orf in infected sheep and lambs
Lambs that are infected or lambs from ewes badly affected with should be bottle fed to reduce the pain and discomfort. The hygiene of all feeding equipment, teats, bottles and utensils is paramount to prevent further spread.
Astringents such as Crystal Violet dressings may help to speed up the animals recovery time. Ewes that have suffered from infection in their teats can be dried up early and administered with antibiotics under vet supervision to prevent a secondary mastitis infection.
Put salt blocks and tubby buckets out and make available to all affected sheep and lambs to help support them to get through it.
If you have an outbreak of orf in your flock vaccinate with Scabivax Forte or other orf vaccine recommended by your vet. To reduce the diseases severity and prevent further spreading of orf through the flock. An applicator is provided with the vaccine to help administer it.
Once orf has been in your flock you should vaccinate annually to help prevent further outbreaks which tend to be a threat annually at lambing once it has occurred once, spring and having young lambs is the most common time for orf outbreaks.
Vaccinating ewes with orf
Ewes should be vaccinated prior to when the disease typically outbreaks but not in the last seven weeks of the ewes pregnancy. The vaccine application is applied by scratching the skin under the front leg.
Vaccinating young lambs with orf
Young lambs are vaccinated for orf by scratching the skin between the foreleg and chest wall anytime from birth. If lambs have not yet been weaned don’t vaccinate them in the groin as they could touch the area with their mouths and risk infecting their mouths and their mothers udder.
Vaccinating older lambs with orf
Older lambs can be vaccinated between the top of their foreleg and their chest wall before leaving the lambing shed to be put to pasture. Vaccinating in contact animals is a crucial aspect to control and to reduce the amount of lambs with the disease. Ensure unvaccinated animals do not come in contact with the animals vaccinated for at least seven weeks post vaccination.
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