Mycobacterium avium subspecies paratuberculosis (MAP) is excreted in large numbers in feces of infected animals and in lower numbers in their colostrum and milk. It is resistant to environmental factors and can survive on pasture for >1 year; survival in water is longer than in soil. The infection is usually acquired through the fecal-oral route; the dose needed to infect an animal is not known. Herds or flocks become MAP-infected by introduction of subclinically infected carriers.
