Johne's Disease is a chronic infection caused by the bacterium Mycobacterium avium subspecies paratuberculosis. It primarily affects the intestines of ruminant animals, such as cattle, sheep, and goats, leading to severe diarrhea, weight loss, and decreased milk production. The disease is slow to develop, often taking years for symptoms to appear. Transmission occurs through contaminated feed, water, or feces, and infected animals can shed the bacteria even before showing signs of illness. There is no cure for Johne's Disease, making prevention through good management practices essential for controlling its spread in livestock populations.