Features
Orf Infection in sheep and lambs
by Dr Peter Nettleton
Orf is a painful skin disease of sheep and goats and is characterised by the development of scabby lesions around the mouth and nostrils of lambs. The infection may also affect other parts, particularly the teats or ewes and lower legs of lambs. Although the disease can strike at any time of the year, infections are most commonly seen in young lambs and their ewes and in older lambs in the late Summer.
The Disease
The disease is caused by a virus which only grows in the surface layers of the skin and in the upper digestive tract. As the virus doesn’t travel throughout the body, sheep can only mount a limited immune response against it. This explains why animals that have recovered from an orf infection (or been vaccinated against orf) can become reinfected in the future.
Orf infection can only establish through broken skin and rough food or pasture may predispose an animal to infection. Once in the skin, the virus multiplies and causes painful scabby lesions at the site of infection commonly on the lips and nostrils. Infection normally runs a course of four to six weeks however lesions can become extensive or secondary infected with bacteria and result in serious disease and sometimes death. The more serious outbreaks are generally associated with intensive sheep husbandry, where there is a build up of infection in buildings.
Lambs infected with orf pose a risk of transmitting the virus to the ewes udder which can lead to mastitis and potentially the loss of the affected half. Suckling lambs with orf lesions may be disinclined to suck and 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.
Treatment of Orf
There is no treatment for orf and as the disease is caused by a virus, it cannot be treated using antibiotics. Most orf infections clear up on their own within a few weeks but you can help prevent the establishment of secondary bacterial infections with the use of topical antibiotic creams, powders or aerosols.
Lambs with severe lesions may have problems feeding and should 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.
The virus will not survive a winter outside but if protected from moisture it can persist in dry buildings for many years. Cleaning and disinfecting buildings is therefore important in the control of orf. The virus is susceptible to most disinfectants and 3% iodophor (FAM) solution or 1% formaldehyde. If applied liberally to thoroughly cleaned surfaces, general purpose disinfectants such as Jeye’s fluid and hypochlorite solutions may also be used.
Protecting your flock from Orf
Vaccinating your flock against orf will help protect your flock and reduce clinical signs and/or lesions of the disease. There is only one vaccine available in the UK; Scabivax Forte, produced by Schering Plough Animal Health. Immunity develops within 4-8 weeks of vaccination and is protective for at least 12 months. This vaccine is a ‘scratch’ vaccine and ewes should be vaccinated behind the elbow or axilla (between the top of the foreleg and the chest wall) using the vaccine applicator.
As Scabivax Forte contains life orf virus, DO NOT use the vaccine on farms which do not have a problem with orf. If vaccinating pregnant ewes, do so no less than seven weeks before lambing and keep them away from the lambing area while the scabs are being shed.
Protecting yourself from Orf
Humans can also become infected with the orf virus through broken skin resulting in localised swollen, red areas which can be extremely painful. Those working with sheep can protect themselves by following good hygienic practices and by wearing protective gloves when handling infected animals. It should also be noted that the vaccine used to protect sheep against orf contains the fully virulent virus and operators must be very careful not to self–inoculate or get vaccines in cuts or abrasions.
Footnote: this article first appeared in the Sheep Farmer magazine and is reproduced with their permission