Mycobacterium indicus pranii vaccine immunoprophylaxis in anti-phenolic glycolipid-1-positive leprosy contacts – A pilot study from a tertiary care center in North India

Background: Contacts of leprosy patients have an increased risk of infection with Mycobacterium leprae. Contact tracing and chemo- or immunoprophylaxis are important means of preventing leprosy transmission. Aims: We aimed to evaluate the efficacy of immunoprophylaxis with Mycobacterium indicus pranii vaccine in reducing anti-phenolic glycolipid-1 titers in household contacts of leprosy patients. Methods: This prospective single-center study was conducted in a tertiary care center in North India from January 2015 to December 2016. Contacts of leprosy patients (both paucibacillary and multibacillary) were screened for anti-phenolic glycolipid-1 antibodies with enzyme-linked immunosorbent assay. Those found positive were given immunoprophylaxis with a single dose of Mycobacterium indicus pranii vaccine, and anti-phenolic glycolipid-1 titers were evaluated at six and 12 months. All contacts were clinically followed for three years. Results: Of the 135 contacts of 98 leprosy patients that were screened, 128 were recruited. Seventeen of these contacts were positive for anti-phenolic glycolipid-1 antibodies and were given Mycobacterium indicus pranii vaccine. Two contacts were lost to follow-up. After immunoprophylaxis, anti-phenolic glycolipid-1 titers were negative in all patients at all intervals, and no contact developed any clinical signs or symptoms of leprosy during the three-year follow-up. Limitations: The small number of contacts studied, the short follow-up period and the absence of a control group were limitations of this study. Dicussion: We could not find any papers on natural decline of PGL 1 titres in contacts, although in leprosy patients, these titres may even increase after completion of treatment. However the titres do correlate with bacterial load (reference: Int J Lepr Other Mycobact Dis. 1998 Sep;66(3):356-64) so if the tires decrease or become negative it may be considered as an indirect evidence of bacillary clearance. Hence we may suggest the protective efficacy. Furthermore, as the editor mentioned, considering the small number of positive patients, a control group was not possible in the present pilot study, but such studies may be carried out in the future. Conclusion: Immunoprophylaxis with Mycobacterium indicus pranii vaccine is effective and safe in preventing disease in contacts of leprosy patients. However, these findings need to be replicated in larger studies.