University of Wisconsin–Madison

Mycobacterium avium subspecies hominissuis (MAH)

This species of mycobacterium is commonly found in soil and water but is generally of low virulence, meaning it has only a limited capacity to cause infection and disease. In animals, pigs have the highest rate of MAH infections. However, they are self-limited infections that cause no obvious disease and are restricted to lymph nodes of the neck region and only seen by meat inspectors at the time of slaughter. In humans children may occasionally get MAH infections in the lymph nodes in their neck. MAH can also infect the intestinal tract of people with AIDS due to the impairment the HIV virus causes to their immune system. The significance of MAH to understanding Johne’s disease is that this microbe is very closely related to MAP and can cause interference with immunological diagnostic testing (cross reactions causing false-positive test results). Other mycobacteria can potentially cause this same problem. However, this is not a very common occurrence in most species.