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This article was published in 1945
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INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.
CONTAGIOUS PUSTULAR DERMATITIS (Scabby Mouth)
VACCINATION AS A PREVENTIVE MEASURE.
J. T. Hayston. B.V.Sc., P.P. Board Research Officer, Glenfield.
Contagious Pustular Dermatitis is an infection of the epidermal tissues of the sheep which is caused by a filterable virus. Almost invariably the lesions become contaminated by organisms such as cocci, but the typical manifestations of the disease may be seen without secondary infection being present. Young lambs most frequently are affected; more mature sheep are affected less commonly and their protection may be due either to a natural age resistance or to an immunity induced from contact with the virus earlier in life.
Under favourable conditions the virus of Scabby Mouth is capable of remaining viable for very long periods, and on certain properties the degree of infection is so heavy that each year an outbreak of the disease occurs. Intravenous, intraperitoneal or oral administration of the virus causes no ill-effect. The virus can cause infection only by invasion of scarified or damaged skin and the presence of thistles and sharp brambles may assist in the spread of an outbreak of the disease.
When the virus is applied to a scarified area of the skin the traumatic injury heals within three days, but by this time a zone of congestion has appeared around the scarified area. After six days small vesicles appear and the lesions reach the pustular stage by the eighth day. By the eleventh day the pustules have developed into dry scabs which eventually fall away. These scabs have a high virus content.
Since the lesions most frequently occur on the skin of the lips of young sheep the associated pain deters the animal from eating. The inner surface of the mouth may be invaded and lesions may be found on the mucosa of the lips, cheek and on the tongue. The resulting loss of condition is sudden and severe, and even starvation may occur from physical inability to prehend food. Where fly-strike is associated with the lesions of Scabby Mouth the mortality may be considerable.
As is the case in all pox-like infections, the disease runs a regular course which is not affected by any therapeutic treatment. However, the secondary infections tend to prolong the course of the disease; and hence the application of antiseptics, emollients and astringents may assist in hastening recovery. Medicaments that have been reported to give results are a solution of iodine in glycerine and a mixture of Stockholm Tar and kerosene.
Lambs can be immunised against Scabby Mouth by inoculating them at marking time with a 1:1000 suspension of desiccated infective scabs in a glycerine and saline mixture. A scarifying needle is dipped in the virus suspension and the inoculation consists of drawing a line on the superficial layers of the skin on the medial. hairless aspect of the hind leg. Under field conditions the immunity resulting from this inoculation has been found to prevent the occurrence of severe losses from contagious postular dermatitis.