Systematic Veterinary Virology

DESCRIPTION

• Contagious pustular dermatitis otherwise known as Scabby mouth, sore mouth or orf is a highly contagious, viral disease of sheep, goats and occasionally humans. It is an acute infectious disease of sheep characterized by the formation of vesicles, pustules, and finally thick scabs on the lips, nostrils, face, eyelids, teats, udders, feet, and occasionally inside the mouth. The disease is widespread in the sheep population and affects all breeds. Lambs are generally more susceptible than adults. The scabby mouth virus infects a sheep through abrasions in the skin. Cool, non-woolled areas such as the mouth, legs, feet, teats and poll are the usual sites of infection. Sheep grazing stubble or on harsh feed are most susceptible to scabby mouth infection due to a higher incidence of minor injuries of the mouth and feet. The mouth and feet are most commonly affected. At first small, reddened areas appear and begin to weep a clear fluid. This fluid eventually hardens into a thick brown scab. In the early stages the scab is firmly attached and if forcibly removed, a raw bleeding area is exposed. After two to three weeks the scabs dry up and drop off. The underlying skin then heals rapidly. Spread within the flock is usually rapid. In most cases the scabs appear at the corner of the mouth and muzzle. In severe cases they cover the lips and spread into the mouth and nostrils. Occasionally scabs occur around the eyes. Scabs on the legs usually occur on the fetlock or coronet. Scabs can also develop on the udder and teats of ewes. Affected ewes may not allow lambs to suckle resulting in lamb losses and reduced weight gain, and affected lambs may find it difficult to feed or suckle normally. Mastitis may also be a problem in a proportion of ewes. Animals that recover from scabby mouth develop a life long immunity to the disease. Sheep of all ages may become affected during the first outbreak on the property, but in subsequent years usually only the lambs are affected. The disease in sheep and goats is normally self-limiting, and clears without treatment within three to four weeks. Early manual removal of scabs will delay healing. Antibiotics are not necessary, unless secondary bacterial infection occurs
• A scabby mouth vaccine is readily available and provides good protection from the disease. The vaccine is applied to the bare skin on the inside of the thigh by scratching with a forked needle that has been dipped in vaccine. This causes a local reaction that does not spread. A line of pustules should appear along the scratch a week later - this indicates a good response and immunity from the vaccine. A sample of vaccinated sheep (about 10 per mob) should be checked between ten and fourteen days after vaccination to ensure a good "take".
• Humans occasionally become infected with the scabby mouth virus. The disease in man is called orf. The usual signs in humans are red papules, which are most often on the hands or arms. Shearers are sometimes affected in the armpit as a result of holding affected feet under their arms. Humans may also become infected from accidental inoculation of the scabby mouth vaccine. Care should be taken to cover scratches and cuts before using the vaccine, and to not accidentally scratch fingers or hands with the vaccine applicator.