GL11

1: Mycobacteriology lab, French National reference center for mycobacteria, University Paris Cité, Inserm UMR1137, GHU APHP Nord, Bichat Hospital, Paris, France
Member of the Technical advisory group of the WHO Global Leprosy programme

Leprosy is one of the oldest infectious diseases, caused by Mycobacterium leprae discovered by Gerhard Armauer Hansen in 1873, i.e. before Robert Koch discovered Mycobacterium tuberculosis. A second leprosy bacilli, M. lepromatosis, was discovered in 2008. Although leprosy appears today as a neglected tropical disease, the infection was all over the world for many centuries before it remains where were concentrated poverty, default in hygiene and lack of medical access, whatever the latitude. Despite significant advances in prevention, treatment, and control, ca. 200 000 new cases of leprosy are notified per year to WHO Global Leprosy Programme. Among these cases, 15% are children below 15 y.o. which demonstrates that transmission of M. lepraeis still ongoing in many countries. It is well known that M. leprae is not growing in vitro, can multiply experimentally in mouse footpads and naturally in nine band-armadillos, resulting in a zoonosis. Bacterial characteristics are the longest bacterial doubling time, estimated as 14 days, growth preference at 33°C, and a small defective genome of 3.27 Mb. This may explain why it multiplies in the skin and peripheral nerves and rarely in other organs. Clinical diagnosis is difficult because the disease manifestations are related to the immune response of the host. Irreversible disabilities are mainly seen when cellular immunity is triggered in tuberculoid forms and leprosy reactions. Strikingly when immune response is low (lepromatous form), clinical signs and symptoms are rare delaying the diagnosis but transmission is the highest. In 2025, diagnosis tools include PCR, WGS and other modern microbiological techniques but still there are no tools for latent infection detection and early diagnosis, especially for neurological forms. Electromyography and nerve echography can help a lot for screening nerve damage, but are still rare in field conditions. Mental health issues affect populations globally, since many countries still have discrimination laws against leprosy patients. Efforts to eliminate leprosy have focused on medical interventions such as multidrug therapy associating dapsone, rifampicin and clofazimine, prevention with BCG vaccination and now with the implementation of post exposure chemoprophylaxis (PEP) given to patient contacts. How much the wide distribution of single dose of rifampicin will increase the risk of antimicrobial resistance in leprosy, is still unknown. Surveillance of AMR starts to be organized but needs resources and new user-friendly techniques. Research and financial helps are still concentrated in old non-governmental organisations, when we know so little about the bacteria, the infection, the transmission and when we need new therapies. New antituberculous drugs, such as bedaquiline and telacebec, might ended as antileprosy agents, for the sake of leprosy patients.