“Mycobacterium avium paratuberculosis is zoonotic. It is possible that MAP infects an individual, and an immune response ensues that limits but does not eradicate the organism, leaving it to survive in macrophages and other reticuloendothelial cells. For reasons that are unclear, this latent infection responds to a “triggering event” that leads to disease. This is analogous to Mycobacterium tuberculosis, which causes a latent infection; the infection activates when immune status changes in the host.”

Oken et al (May 2017)