Johne's disease is a fatal infection that affects primarily the small intestine of ruminants. It is caused by Mycobacterium avium subspecies paratuberculosis (M. avium subsp. paratuberculosis). It is a chronic and contagious disease of ruminants characterized by chronic diarrhoea, progressive emaciation and thickening of the intestine (corrugations). It particularly affects cattle, sheep, goat and wild ruminant, but rare in other animals. It causes major economic loss to farmers and livestock industry in terms loss of production and animal death. Lack of knowledge about its transmission and prevention among the farmers and farm workers lead to spread of this disease to the healthy animals and human. This article reviews some information about clinical signs, transmission and prevention of Johnes? disease.