Barriers to Dermatopilus dermatonomus infection on the skin of sheep

Abstract

In adult Merino sheep, but not in coarser-woolled breeds, the greasy fleece and the film of sebaceous wax on the underlying skin were found to be efficient barriers to infection with Dermatophilus dermatonomus. Severe infection resulted from the application of liquid cultures after the removal of wax with light petroleum. On several non-woolled regions resistance was shown to depend on the thickness and integrity of the stratum corneum.

A study was made of the development of the sebaceous film and of its properties. It was shown that the rate of formation of the protective film was not affected by differences in atmospheric temperature, or by the moderate reduction in wax output observed both in pregnant ewes and in wethers given large doses of oestrogen. It was found that variations in the bacteriostatic action and melting point of sebum did not affect the protectiveness of the film or the ability of naturally infected sheep to overcome the disease.

Outbreaks of body infection commonly commence in Merinos soon after birth or shearing, and between the ages of about 3 and 12 months. These were shown to be times when the fleece, and the wax film on the skin, provide inadequate protection. Pronounced fluctuations in susceptibility were observed on the face and ears, which are important reservoirs of infection, and were shown to be associated with natural variations in the integrity of the wax film on the face and of the stratum corneum on the ears.