Johne's disease, which has a worldwide distribution, is caused by infection with mycobacterium avium subspecies paratuberculosis, MAP, and most cattle are generally infected early in life by ingestion of MAP through colostrum, milk, faecal contaminated teats, water, feeds or surfaces. Adult animals can become infected but it is rare, and they usually have other problems such as deficiencies with their immune system.
Typically, most cases develop clinical signs between the ages of two and six years with the onset of clinical symptoms being precipitated by intensive farming systems, acid soils, poor nutrition, stress related transport, lactation, calving and immunosupression by other biological agents such as bovine virus diarrhoea, BVD, or by deficiency of essential elements. The disease can cause significant animal production and welfare problems. There is no satisfactory treatment and the majority of animals showing clinical symptoms will eventually die of the disease.