Antibodies to a synthetic analog of phenolic glycolipid-I of Mycobacterium leprae in healthy household contacts of patients with leprosy.

Fifty-four household contacts of lepromatous patients, 39 household contacts of tuberculoid patients, and 99 control persons were examined with an enzyme-linked immunosorbent assay for their antibody responses to phenolic glycolipid-I (PGL-I) of Mycobacterium leprae using a synthetic analog (PGL-ISA) with the same terminal sugar epitope, namely, O-(3, 6-di-O-methyl-beta-D-glucopyranosyl)-(1----4)-O-(alpha-L-rhamnopyranosyl )-(1----9)-oxynonanoyl-BSA. This study was conducted in the Gurage area of Ethiopia in 15 households with a leprosy patient and 15 matched control households. Household contacts with more than 1 year of exposure to a lepromatous patient had antibodies to PGL-ISA significantly more often (19 of 34 persons) than did household contacts with less than 1 year of exposure to a lepromatous patient (4 of 20 persons), household contacts of tuberculoid patients (8 of 39 persons), and persons without exposure to leprosy in the household (33 of 99 persons). No significant association was found between the prevalence of antibodies to PGL-ISA in the household contacts and disease activity in the lepromatous index patients at the time of examination; nor was there a significant association between antibody responses and age or sex of the contacts. The increased prevalence of antibodies to M. leprae antigen in healthy persons with more than 1 year of contact with a lepromatous patient provides further evidence that subclinical infection in leprosy is common, and is related to the type of leprosy in the index patient. The fact that antibodies to PGL-ISA were detected in one third of the persons without household exposure to leprosy emphasizes the necessity to always include comparable controls from the same endemic area in studies of leprosy contacts.