DNA typing of Johne's disease organisms

Summary

This study was undertaken to detennine whether Johne's disease in sheep and cattle in Australia can be considered to be separate diseases subject to independent control programs. Isolates of the bacterium that causes Johne's disease, namely Mycobacterium avium subsp. paratuberculosis, were typed genetically in order to see whether those in sheep were different to those in cattle. About 350 separate isolates were evaluated from about 100 farms in New South Wales, Victoria, Tasmania and South Australia. A new test was developed to enable the bacterium to be typed quickly and accurately. Johne's disease in sheep was almost always due to sheep strains of M avium subsp. paratuberculosis while cattle were almost always infected with cattle strains. However, it was concluded that Johne's disease has occasionally spread from sheep to cattle in New South Wales, probably under unusual circumstances. Johne's disease may also spread from sheep to goats. As a result of this project Johne's disease control programs were assessed on an ongoing basis as more information is obtained about the way the disease may be spread between farm animals.