A study on the methods for early serological diagnosis of leprosy and their potential use

This is a serial study. In this series we have established 12 methods for the early serological diagnosis of leprosy, including the FLA-ABS test, ELISAs with artificial products (ND-O-, ND-P-, NT-O-, NT-P-BSA; PGL-I, whole M. leprae and M. smegmatis), monoclonal antibody specific binding assay (McAb/SBA), latex agglutination test (LAT), and MLPA. These methods were compared with each other on a large scale in leprosy patients and in the field. The results indicate that 1) Excellent results were obtained when ELISAs were conducted with skim milk or egg albumin as the blocking agent and by using blood from earlobes instead of from venipuncture. 2) According to the four "S" standard (sensitivity, specificity, simplicity and speed), among the 12 methods the ND-O-BSA-ELISA (ND-ELISA) is the best and the MLPA is more suitable for use in the field because it is simple and rapid. 3) In the ND-ELISA, the increase or decrease of the OD value has a positive correlation with the BI, and the order of positive rates was a) in various types of leprosy: LL > BL > BB > BT > TT; b) in household contacts (HC), random population (RP), normal controls in endemic areas (ENC) and normal controls in nonendemic areas (NNC): HC > RP > ENC > NNC. 4) In a population with subclinical M. leprae infection, the highest risk group was between the ages of 15 and 25 and had an increase or a persistence of high OD values prior to onset of disease. 5) OD values gradually decreased over time following treatment and these declines paralleled declines in the BI. 6) In cases cured with dapsone therapy, there was an increase or a persistence of high OD values in ND-ELISA prior to the onset of a leprosy relapse. In conclusion, we have compared and evaluated 12 immuno-assays and have shown that the ND-ELISA is the most practical one for use in investigating sero-immunological epidemiology, subclinical infection with M. leprae, early detection of disease, monitoring of antimicrobial therapy, and even for the prediction of leprosy relapse.