Tuberculosis transmission: Why the strains of Mycobacterium bovis are not transmitted between humans as Mycobacterium tuberculosis does?

In the beginning of the XXI century, tuberculosis still causes three deaths every minute and 8 million people become infected each year. A possible explanation for the successful transmission of this disease relies on the aerial propagation from infected patients. Tuberculosis also affects a variety of mammals including cattle, but disease in humans and animals is caused by different species of the Mycobacterium genus: Mycobacterium tuberculosis and Mycobacterium bovis respectively. However, it is worthy to remember that bacteria responsible for tuberculosis in cattle are rarely transmitted to and between humans.