The Importance of Immune Response to Leprosy

It's estimated that around 95% of the human population is essentially immune to leprosy. Leprosy has a very, very low infectivity. If you took a random sample of a hundred people and inoculated them with the mycobacterium bacterium, only about five of them would actually become infected. It evolved millions of years ago, along with humans,. It's a really interesting little bacterium.