Bolo disease: a specific, localised skin disease of woolled sheep.

Bolo disease is limited to Merino and Döhne merino sheep in the Stutterheim and Cathcart districts of the eastern Cape Province. It occurs under natural grazing conditions regardless of the season of the year and the condition of the natural grazing. Ewes and wethers are most frequently affected. Skin lesions are well-defined, and the corresponding fleece has dark-grey to almost black spots, patches or bands varying in number, size and distribution between individual sheep. The wool in the affected areas is visibly shorter, less dense and tender, and the tips of the staples are spiky. In freshly-shorn sheep, the affected areas appear chalky white. Chronic and superimposed acute lesions are present in the same specimen histologically. Skin lesions include superficial and follicular hyperkeratosis, acanthosis, and sebaceous gland hyperplasia and hypertrophy. These changes are accompanied by dilatation of some of the follicles in the midshaft area, and collapse of the subepidermal tissue with only a few remaining collagen fibres separating the follicles and the sebaceous glands from the thickened epidermis. Corynebacterium spp. is the most consistent bacterium isolated from the lesions. Lesions produced by suspensions of this organism simulated both clinical signs and histopathological findings of the natural condition.

Bolo disease: a bacteriological survey.

A total of 718 sheep, 381 severely and 190 mildly affected with Bolo disease as well as 147 visibly unaffected animals emanating from 15 farms in the Stutterheim and Cathcart districts in the eastern Cape were subjected to bacteriological examination of skin surfaces and wool specimens. Altogether, 1,168 specimens were examined. These included skin swabs, skin scrapings and wool samples. Corynebacterium spp represented 94.4% of the primary isolates in cultures prepared from all specimens and 97.2% in those derived from skin swabs only, while a variety of other bacteria collectively constituted the remainder of primary isolates. In all, Corynebacterium spp was isolated from specimens of 94.2% of sheep severely affected with Bolo disease and from 83.7% of those mildly affected, whereas it could only be isolated from 1.36% clinically unaffected sheep. In a comparative study, swabs taken directly from the skin surface, proved to be the method of choice for the collection of specimens for bacteriological examination of Bolo disease. Using this method, Corynebacterium spp. was isolated from 98.7% of severely, and 85.3% of mildly affected sheep as well as 4% of sheep apparently unaffected by Bolo disease. The isolation of Corynebacterium spp. from skin scrapings collected from the 3 categories of affection (73.3%, 57.3% and 4% respectively) and from wool samples (52%, 41.3% and 1.3% respectively) proved these 2 methods of sampling to be less reliable. A close association has been established between the incidence of Corynebacterium spp. and the occurrence of clinical Bolo disease.