An epidemiological study of leprosy infection by serology and polymerase chain reaction

A population-based study has been carried out in two adjacent villages in a highly leprosy-endemic area of South Sulawesi, Indonesia. The prevalence of clinical leprosy was 10.0 per 1000 inhabitants. A total of 1015 serum samples and 1228 nasal swab specimens were collected. IgM antibodies in blood to phenolic glycolipid-I (PGL-I) of Mycobacterium leprae were demonstrated by the gelatin particle agglutination test (MLPA) and by indirect ELISA (IgM-PGL). IgG antibodies to PGL-I (IgG-PGL) and lipoarabinomannan-B (IgG-LAM) were measured by indirect ELISA. The presence of M. leprae in nasal swab specimens was established by a polymerase chain reaction (PCR). The seropositivity rates in the population were 32% for MLPA, 30.8% for IgM-PGL, 6.7% for IgG-PGL, and 11.6% for IgG-LAM. Seropositivity rates for MLPA and IgM-PGL were highest in the younger age groups. There was no difference in seropositivity in any of the tests between household contacts of leprosy patients and noncontacts. The seropositivity rates in the MLPA and IgM-PGL were not randomly distributed among all households. The presence of M. leprae by PCR was demonstrated in 7.8% of the nasal swab specimens. No correlation was found between the results of the PCR and serology. This study indicates that M. leprae is widespread in the population, and that in endemic areas many individuals carry M. leprae in their nasal cavities without having obvious symptoms of leprosy.