People pretty much are still immune to leprosy: > It is estimated that more than 95% of people who are infected with Mycobacterium leprae do not develop lepros

People pretty much are still immune to leprosy: > It is estimated that more than 95% of people who are infected with Mycobacterium leprae do not develop leprosy because their immune system fights off the infection. People who develop leprosy may have genes that make them susceptible to the infection once they are exposed. [0] Leprosy is rare [1], and fairly hard to transmit. You have to have either had close contact with someone with the disease, or have handled an armadillo [2] to contract leprosy. It is impossible to culture in a lab [3] because it's so well adapted to living inside a human cell [ibid]. And, it's in the same genus as the bacterium that causes tuberculosis. If anything, Mycobacterium leprae is extremely well adapted to survival and propagation, because it doesn't make us sick very often, progresses slowly [4], and, importantly, doesn't kill us. --- [0]: https://www.merckmanuals.com/home/infections/tuberculosis-and-related-infections/leprosy https://www.merckmanuals.com/home/infections/tuberculosis-an... [1]: https://www.who.int/news-room/fact-sheets/detail/leprosy https://www.who.int/news-room/fact-sheets/detail/leprosy: "Elimination of leprosy as public health problem (defined as a registered prevalence of less than 1 case per 10 000 population) was achieved globally in 2000." [2]: https://www.aad.org/public/diseases/a-z/leprosy-risk https://www.aad.org/public/diseases/a-z/leprosy-risk lists "[living] in a country where leprosy is more common, such as India, Brazil, China, Indonesia, or parts of Africa," along with hanging out with armadillos as the only real risk factors for someone in the US. [3]: https://microbewiki.kenyon.edu/index.php/Host_Dependency_of_Mycobacterium_leprae https://microbewiki.kenyon.edu/index.php/Host_Dependency_of_... [4]: https://www.webmd.com/skin-problems-and-treatments/guide/leprosy-symptoms-treatments-history#1 https://www.webmd.com/skin-problems-and-treatments/guide/lep... says "It usually takes about 3 to 5 years for symptoms to appear after coming into contact with the leprosy-causing bacteria. Some people do not develop symptoms until 20 years later."