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Farming issues Mhlupheki Dube
THIS week we will look at one of the common diseases in goats and sheep. The disease is commonly known as orf or sore mouth while it is scientifically known as contagious ecthyma. This shows in your goats as dry blisters around the mouth of your goats and sheep. This disease is caused by a parapox virus and infection results in a contagious pustular dermatitis, mainly in sheep and goats. The virus is epitheliotropic, which means that it has an affinity for the skin and infection occurs by direct contact. In young lambs and kids, typical growths and swellings are seen on the skin around the lips and nostrils.
Young animals are the most susceptible to contracting the disease. In adult sheep and goats, the typical growths can occur on the muzzle but are also seen on the face, ears, teats and vulva. It is a zoonotic disease which means it can be transmitted between animals and humans. Sore mouth outbreaks occur more frequently during periods of extreme temperatures such as late summer and winter.
The disease initially presents itself as papules (elevation of the skin) that progress to blisters or pustules before encrusting. These lesions are found in the skin of the lips. They can spread around the outside and inside of the mouth, face, lips, ears, vulva, scrotum, teats, and feet, usually in the interdigital region. Extensive lesions on the feet can lead to lameness in adults and young animals. The infection is spread by direct and indirect contact from infected animals or by contact with infected tissue or saliva containing the virus. Blisters eventually break down to release more of the virus and later develop into wet pus-like scabs.
These lesions can persist for three weeks and can become a site for the development of secondary bacterial infections. Scab tissues are extremely painful, to the point of preventing sick animals from eating. Outbreaks of orf seem to be associated with the lambing (kidding) season. Suckling lambs infected with orf run the risk of transmitting the virus to the ewe’s udder which can lead to mastitis and potentially the loss of the affected half of the udder. Lambs with orf lesions may be disinclined to suck and, equally, ewes with sore teats may not let their lambs feed.
Together this can result in undernourished lambs and/or the virus being spread to other ewes as infected lambs try to feed from others. Although infected animals develop antibodies against the virus, these antibodies do not provide good protection and explains why animals which have recovered from an orf infection or even those vaccinated against orf can become re-infected by the virus at a later date. It is important to note that contagious ecthyma virus cannot penetrate intact skin hence abrasion of skin caused by thorns and spiky plants facilitates penetration of the virus.
The main economic effects of orf in your goats or sheep are related to the deaths of young lambs and kids that cannot suckle due to painful lesions on the lips and nostrils. Also the flock fertility, kidding or lambing percentage can also be affected if lesions appear on the prepuce or vulva, during the breeding season as mating becomes extremely painful.
There is no treatment for orf like most diseases caused by a virus. Most orf infections clear up on their own within a few weeks but the use of antibiotic paints, powders or aerosols can help prevent the establishment of secondary bacterial infections. Lambs with severe lesions or where their ewe does not let them suck, may have to be fed artificially to minimise weight loss. Ewes which are affected on the teats or udder should receive special attention to ensure that they do not develop mastitis. Since the scabs that form during an orf infection are full of viruses the biggest source of infection from one lambing season to the next is from the scabs that are shed from infected animals as they heal. Although the virus in the scabs will not survive a winter outside in damp conditions it can persist in dry buildings for many years. Cleaning and disinfecting buildings particularly if they are used for lambing is therefore important in the control of orf.
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