Recent advances in treatment have achieved a large drop in the prevalence of active leprosy cases, but the incidence is at best decreasing slowly. Most people within leprosy-endemic populations have been exposed to Myco bacterium leprae, but few develop disease and it seems likely that the majority of the population develops protective immunity. If the site of initial infection is in the nose, dissemination of bacilli around the body to skin and nerve implies that the initial infection is

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... iferous and it has been shown that nasal M. leprae are detectable by polymerase chain reaction (PCR) of nasal swabs. Since salivary anti-M. leprae IgA (sMLIgA) levels are correlated with protection, 5 we have surveyed groups ofleprosy patients, contacts and the general population for both their sMLIgA and nasal PCR positivity. A total of 304 subjects were enrolled in the study: PCR and mucosal challenge tests were performed in 204 of these individuals. sMLIgA was present in 66% of treated patients, 76% of leprosy workers and 72% of healthy contacts. However, only 33% of indigenous subjects were sMLIgA+, in contrast to the earlier studies showing 74% positivity. 5 PCR for M. leprae was present in both household contacts (2%) and indigenous controls (5%). In a subsequent fo llow-up study, nasal swabs were taken from 97 of those studied in the first series: three PCR+ individuals followed up after one year became negative, while of the remaining 94 PCR-individuals retested, 2