Utility of serodiagnostic tests for leprosy: a study in an endemic population in South India.

In order to evaluate the usefulness of natural disaccharide (PGL1) and 35 kDa antigens based serology in diagnosis of leprosy and in detecting high risk groups for leprosy, this study was conducted in an endemic population in South India. Out of 3346 cases and their households and neighbouring household contacts, serum samples from 2994 and 2875 individuals were screened for antibodies against PGL1 and 35kDa antigens respectively. While the overall positivity for contacts and leprosy cases was 3.3% for PGL1 antibody, the positivity for 35 kDa antibody was 6.3%. The positivity for contact population was 2.7% and 5.4% for PGL1 and 35 kDa antibodies, respectively. Lepromatous and borderline lepromatous patients showed positivity of 35.1% for PGL1 antibody and 45.7% for 35 kDa antibody. Follow-up of contacts showed that the majority (>90%) remained seronegative for both the antibodies and most of the new cases emerged from the seronegative group. The study clearly indicates that specific serological assays are not sensitive enough for application, both for diagnosis and for identifying any individual at risk for leprosy in the south Indian endemic population.