Molecular Epidemiology of Mycobacterium avium subsp. paratuberculosis on Dairy Farms.

Mycobacterium avium subspecies paratuberculosis (MAP) is the etiological agent of severe chronic intestinal inflammatory disease in ruminants, termed Johne's disease, and can infect many other animal species, including humans. MAP has a long incubation period prior to manifestation of clinical signs including diarrhea, weight loss, and loss of production. MAP has a high prevalence in dairy herds and results in considerable adverse impacts on animal health and productivity throughout the world. Recent investigations have leveraged the characterization of the MAP genome for the development of powerful new molecular techniques for MAP strain differentiation. These approaches are providing key insights into the epidemiology and transmission of MAP on and between dairy herds. We summarize the state of the art for MAP diagnostics and strain differentiation and our current knowledge of mechanisms of within- and between-herd transmission of MAP, along with future needs for the development of rational MAP infection control programs.