Observations on tuberculosis caused by Mycobacterium bovis in sheep

Abstract

In a flock of 15,000 sheep Mycobacterium bovis was recovered from 32 (74.4%) of 43 individuals with tuberculous lesions. The flock was pastured on a property which had a history of severe and extensive tuberculosis in cattle and opossums (Trichosurus vulpecula).

Tuberculous lesions were concentrated in the posterior of the thoracic and anterior part of the abdominal cavities. A few sheep had lesions in the lymph nodes of the head and neck. The distribution suggested an oral route of infection. The microscopic appearance of the lesions was that of the typical granuloma with a caseous centre, but the gross appearance, that of an abscess with a thin capsule and copious central sticky mucoid pus was not typical of the usual appearance of tuberculous lesions as seen in cattle.

Thirty-one reactors were identified in a group of 281 sheep tuberculin tested by single intradermal injection of 0.1 ml of 1 mg/ml PPD tuberculin in the skin of the thigh. Thirty of the 31 reactors had lesions as did 7 non-reactors. The tuberculin test applied had a sensitivity of 81.6% and a specificity of 99.6%. The investigation reported indicated that sheep are quite susceptible to infection with M. bovis.