Prevalence of IgM antibodies to phenolic glycolipid I among household contacts and controls in Korea and the Philippines

Impact of PGL-I seropositivity on the protective effect of BCG vaccination among leprosy contacts: a cohort study

Background

Contacts of leprosy patients are at increased risk of developing leprosy and need to be targeted for early diagnosis. Seropositivity to the phenolic glycolipid I (PGL-I) antigen of Mycobacterium leprae has been used to identify contacts who have an increased risk of developing leprosy. In the present study, we studied the effect of seropositivity in patient contacts, on the risk of developing leprosy, stratified by Bacille Calmette Guerin (BCG) vaccination after index case diagnosis.

Methodology/Principal Findings

Leprosy contacts were examined as part of the surveillance programme of the Oswaldo Cruz Institute Leprosy Outpatient Clinic in Rio de Janeiro. Demographic, social, epidemiological and clinical data were collected. The presence of IgM antibodies to PGL-I in sera and BCG vaccination status at the time of index case diagnosis were evaluated in 2,135 contacts. During follow-up, 60 (2.8%; 60/2,135) leprosy cases were diagnosed: 41 among the 1,793 PGL-I-negative contacts and 19 among the 342 PGL-I-positive contacts. Among PGL-I-positive contacts, BCG vaccination after index case diagnosis increased the adjusted rate of developing clinical manifestations of leprosy (Adjusted Rate Ratio (aRR) = 4.1; 95% CI: 1.8–8.2) compared with the PGL-I-positive unvaccinated contacts (aRR = 3.2; 95% CI: 1.2–8.1). The incidence density was highest during the first year of follow-up for the PGL-I-positive vaccinated contacts. However, all of those contacts developed PB leprosy, whereas most MB cases (4/6) occurred in PGL-I-positive unvaccinated contacts.

Conclusion

Contact examination combined with PGL-I testing and BCG vaccination remain important strategies for leprosy control. The finding that rates of leprosy cases were highest among seropositive contacts justifies targeting this specific group for close monitoring. Furthermore, it is recommended that PGL-I-positive contacts and contacts with a high familial bacteriological index, regardless of serological response, should be monitored. This group could be considered as a target for chemoprophylaxis.

Although leprosy has become a neglected disease, it is an important cause of disability, and 250,000 new cases are still diagnosed worldwide every year. The current study was carried out in Brazil, where almost 40,000 new cases of leprosy are diagnosed every year. The study targeted contacts of leprosy patients, who are at the highest risk of contracting the disease. We studied 2,135 contacts who were diagnosed at the Leprosy Outpatient Clinic at the Oswaldo Cruz Foundation in Rio de Janeiro, RJ, Brazil, between 1987 and 2007. The presence of antibodies against a specific Mycobacterium leprae antigen (PGL-I) at the first examination and BCG vaccination status were evaluated. PGL-I-positive contacts had a higher risk of developing leprosy than PGL-I-negative contacts. Among the former, vaccinated contacts were at higher risk than unvaccinated contacts. Our results indicate that contact examination combined with PGL-I testing and BCG vaccination appears to justify the targeting of PGL-I-positive individuals for enhanced surveillance. Furthermore, it is highly recommended that PGL-I-positive contacts and contacts with a high familial bacterial index (i.e., the sum of results from index and co-prevalent cases), regardless of serological response, should be monitored. This group could be considered as a target for chemoprophylaxis.

Antigen discovery: a postgenomic approach to leprosy diagnosis

Leprosy is an infectious, neurodegenerative disease of humans caused by Mycobacterium leprae. Despite effective control programs, the incidence of leprosy remains stubbornly high, suggesting that transmission may be more common than expected. The rationale of this work was to use bioinformatics and comparative genomics to identify potentially antigenic proteins for diagnostic purposes. This approach defined three classes of proteins: those restricted to M. leprae (class I), those present in M. leprae with orthologues in other organisms besides mycobacteria (class II), and exported or surface-exposed proteins (class III). Twelve genes (two class I, four class II, and six class III proteins) were cloned in Escherichia coli, and their protein products were purified. Six of these proteins were detected in cell extracts of M. leprae by immunoblotting. The immunogenicity of each recombinant protein was then investigated in leprosy patients by measuring the reactivity of circulating antibody and gamma interferon (IFN-gamma) responses in T-cell restimulation assays. Several class II and class III proteins were recognized by circulating antibodies. Importantly, most class II proteins elicited IFN-gamma responses that were significantly stronger than those produced by previously identified antigens. Among them, two class II proteins, ML0308 and ML2498, showed marked humoral and cellular immunogenicity, therefore providing promising candidates for the diagnosis of both tuberculoid and lepromatous forms of leprosy.

Genotyping of Mycobacterium leprae on the basis of the polymorphism of TTC repeats for analysis of leprosy transmission

The polymorphism of TTC repeats in Mycobacterium leprae was examined using the bacilli obtained from residents in villages at North Maluku where M. leprae infections are highly endemic (as well as from patients at North Sulawesi of Indonesia) to elucidate the possible mode of leprosy transmission. TTC genotypes are stable for several generations of passages in nude mice footpads and, hence, are feasible for the genotyping of isolates and epidemiological analysis of leprosy transmission. It was found that bacilli with different TTC genotypes were distributed among residents at the same dwelling in villages in which leprosy is endemic and that some household contacts harbored bacilli with a different genotype from that harbored by the patient. Investigations of a father-and-son pair of patients indicated that infections of bacilli with 10 and 18 copies, respectively, had occurred. Genotypes of TTC repeats were found to differ between a son under treatment and two brothers. These results reveal the possibility that in addition to exposure via the presence of a leprosy patient with a multibacillary infection who was living with family members, there might have been some infectious sources to which the residents had been commonly exposed outside the dwellings. A limited discriminative capacity of the TTC polymorphism in the epidemiological analysis implies the need of searching other useful polymorphic loci for detailed subdivision of clinical isolates.

Distribution and persistence of Mycobacterium leprae nasal carriage among a population in which leprosy is endemic in Indonesia

In order to understand better the relationship among Mycobacterium leprae, its transmission and the human host or the chain of infection which may lead to the development of leprosy, we performed a population survey in which nasal carriage of M. leprae was determined by a specific polymerase chain reaction (PCR), 2 years after an earlier survey in the same population. 1923 persons were registered, 1171 were clinically examined for signs of leprosy, and 418 were tested by PCR. The detection rate of leprosy in the study area had not changed significantly during the 2 years' observation period since the introduction of multi-drug therapy, i.e. 6/1000 compared to 7.7/1000 2 years before. Of 6 newly detected cases, 5 were diagnosed as having paucibacillary leprosy. The presence of M. leprae could be demonstrated by PCR in 2.9% (12/418) of the persons. PCR positivity was not persistent over the 2 years. All the PCR positive persons identified in the first survey were negative in the second, indicating that M. leprae nasal carriage is transient. As in the previous survey, we found evidence for widespread M. leprae nasal carriage as determined by PCR among the general population in an area in which leprosy is endemic. In addition, our data indicated that PCR positivity can occur in certain clusters in the community. This clustering seems to be time-dependent, not necessarily related to the presence of patients.

Detection of Mycobacterium leprae nasal carriers in populations for which leprosy is endemic

In order to better understand the role of Mycobacterium leprae nasal carriage in the maintenance of infection reservoirs and transmission of leprosy, we applied a polymerase chain reaction (PCR) that detected a 531-bp fragment of the pra gene of M. leprae on nasal swab specimens collected through a total population survey from individuals living in an area in which leprosy is endemic. Among the total tested population of 1,228 people, 7.8% were found to be PCR positive. PCR positivity was shown to be randomly distributed among the population for which leprosy is endemic. No association was observed between PCR positivity, age, or sex. The observed distribution of PCR positivity among households of different sizes confirmed the expected values, with the exception of two households, each with three people with PCR-positive nasal swab specimens. Although nasal carriage does not necessarily imply infection or excretion of bacilli, the finding of nasal carriage supports the theory of a disseminated occurrence of M. leprae in populations for which leprosy is endemic.

Subclinical infection with Mycobacterium leprae--a problem for leprosy control strategies

Tests for the serodiagnosis of leprosy, including those based on phenolic glycolipid-I (PGL-I), have shown poor specificity for leprosy in studies of endemic communities, despite initially promising results in studies of selected patients. During a 5 years follow-up study of a hyperendemic community in Papua New Guinea, a marked reduction in numbers of seropositive children and an increase in age of those seropositive followed introduction of multi-drug therapy. This was accompanied by a reduced case detection rate and a shift to paucibacillary disease in new cases, consistent with a reduction in transmission. Only a minority of persistently seropositive persons developed leprosy. These observations suggest that subclinical infection with Mycobacterium leprae is common in endemic communities and that PGL-I seropositivity is a marker of subclinical infection, with poor specificity for overt disease. Detection of subclinical infection may confound control strategies which use screening tests to identify asymptomatic highly infectious cases for earlier therapy.