Recent advances in immunodiagnosis of leprosy

Although prevalence of leprosy is considerably reduced, the unabated emergence of about 300,000 cases worldwide indicates that the source of infection and transmission are not being addressed. Early diagnosis and treatment still remain the cornerstone of leprosy control. Many diagnostic issues hinder the correct and timely diagnosis and classification of leprosy. Delayed and missed diagnosis of infectious leprosy patients and the lack of tests to measure asymptomatic M. leprae infection in contacts also hamper the assessment of transmission of M. leprae infection. An important goal would be the development of improved diagnostic tools to diagnose difficult cases and to detect M. leprae infection before clinical manifestation. The search for an ideal immunodiagnostic tool for leprosy had gone through various phases and development over the years, with inherent limitations in the sensitivity and specificity of the immunodiagnostic tests for leprosy. With improvement in technology many modifications of previously used PGL-1 assay in the form of rapid and less expensive techniques, such as dipstick, ELISA, ML flow test, have been introduced. Many new skin test antigens with potential for improving their efficiency, such as MLSA LAM, MLCwA and their fractionates, have been studied. After the completion of genome sequencing of M. leprae in 2000, many genes that were studied in M. tuberculosis and found potential for the immunodiagnosis of tuberculosis, such as CFP-10 and ESAT-6 proteins, have been investigated in M. leprae also. Genes that are unique to M. leprae with no homologous in M. tuberculosis have been explored for novel M. leprae-specific antigens. In order to overcome the problem of cross-reactivity, a number of workers have synthesized overlapping short peptides of different M. leprae recombinant proteins and studied their sequence divergence and attempted to identify M. leprae-specific B- and T-cell epitopes. This review makes an effort to present an overview of all these developments in the field of immunodiagnosis of leprosy.