Household contacts of leprosy patients are the group with the highest risk of developing the disease, and although many risk or prevention factors have been identified, they have not been employed in leprosymonitoring programs. This investigation aimed to establish the relative risks or the preventive effects of the presence of BCG vaccination, the Mitsuda test, and the ML-Flow assay. Household contacts (1,396) were monitored for a 5-year period. Twenty-eight contacts (2%) developed leprosy and had their clinical and operational classifications established. All immunological tests were performed, and intradermal BCG vaccination was given after the BCG scar count. Of the affected contacts, 75% developed the disease in the first year, and 71.4% were classified as having paucibacillary forms. Contacts of lepromatous leprosy patients presented a 3.8-fold-higher risk of developing leprosy. BCG vaccination and the Mitsuda test showed a protective effect against leprosy of 0.27 (at least one scar) and 0.16 (>7 mm), respectively, and the positive ML-Flow test indicated a relative risk approximately sixfold higher for occurrence of the disease. All unfavorable combinations of two and three assays generated significant risk values that ranged from 5.76 to 24.47, with the highest risk given by the combination of no BCG scar, negative Mitsuda test, and positive ML-Flow test. We suggest that the BCG vaccination may be given to stimulate Mitsuda test positivity, reducing the patient's risk of developing multibacillary forms. The high significance of these tests may have a great impact on programs to monitor contacts and should be used to improve early detection and treatment.

Leprosy transmission still occurs despite the availability of highly effective treatment. The next step towards successfully eliminating leprosy is interrupting the chain of transmission of the aetiological agent, Mycobacterium leprae. In this investigation, we provide evidence that household contacts (HHCs) of leprosy patients might not only have subclinical infections, but may also be actively involved in bacilli transmission. We studied 444 patients and 1,352 contacts using anti-phenolic glycolipid-I (PGL-I) serology and quantitative polymerase chain reaction (qPCR) to test for M. leprae DNA in nasal swabs. We classified the patients according to the clinical form of their disease and the contacts according to the characteristics of their index case. Overall, 63.3% and 34.2% of patients tested positive by ELISA and PCR, respectively. For HHCs, 13.3% had a positive ELISA test result and 4.7% had a positive PCR test result. The presence of circulating anti-PGL-I among healthy contacts (with or without a positive PCR test result from nasal swabs) was considered to indicate a subclinical infection. DNA detected in nasal swabs also indicates the presence of bacilli at the site of transmission and bacterial entrance. We suggest that the concomitant use of both assays may allow us to detect subclinical infection in HHCs and to identify possible bacilli carriers who may transmit and disseminate disease in endemic regions. Chemoprophylaxis of these contacts is suggested

Leprosy epidemiological studies have been restricted to Mycobacterium leprae DNA detection in nasal and oral mucosa samples with scarce literature on peripheral blood. We present the largest study applying quantitative real‐time PCR (qPCR) for the detection of M. leprae DNA in peripheral blood samples of 200 untreated leprosy patients and 826 household contacts, with results associated with clinical and laboratory parameters. To detect M. leprae DNA a TaqMan qPCR assay targeting the M. leprae ML0024 genomic region was performed. The ML0024 qPCR in blood samples detected the presence of bacillus DNA in 22.0% (44/200) of the leprosy patients: 23.2% (16/69) in paucibacillary (PB), and 21.4% (28/131) in multibacillary (MB) patients. Overall positivity among contacts was 1.2% (10/826), with similar percentages regardless of whether the index case was PB or MB. After a follow‐up period of 7 years, 26 contacts have developed leprosy. Comparing the results of healthy contacts with those that become ill, ML0024 qPCR positivity at the time of diagnosis of their index case represented an impressive 14.78‐fold greater risk for leprosy onset (95% CI 3.6–60.8; p <0.0001). In brief, contacts with positive PCR in blood at diagnosis of index cases are at higher risk of later leprosy onset and this marker might be combined with other prognostic markers for management of contacts, which requires further studies.

This cross-sectional retrospective study evaluated 440 leprosy patients; 57% (251/440) had leprosy reactions during and/or after multidrug therapy, 80.5% (202/251) of whom presented with multibacillary leprosy. At diagnosis, positive bacterial index (BI) [odds ratio (OR) = 6.39; 95% confidence interval (CI): 4.1-10.1)] or polymerase chain reaction (PCR) (OR = 9.15; 95% CI: 5.4-15.5) in skin smears, anti-phenolic glycolipid-1 (anti-PGL-1) ELISA (OR = 4.77; 95% CI: 2.9-7.9), leucocytosis (OR = 9.97; 95% CI: 3.9-25.7), thrombocytopenia (OR = 5.72; 95% CI: 2.3-14.0) and elevated lactate dehydrogenase (OR = 2.38; 95% CI: 1.4-4.0) were potential markers for the development of reactions during treatment. After treatment, positive BI (OR = 8.47; 95% CI: 4.7-15.3) and PCR (OR = 6.46; 95% CI: 3.4-12.3) in skin smears, anti-PGL-1 ELISA (OR = 2.25; 95% CI: 1.3-3.9), anaemia (OR = 2.36; 95% CI: 1.2-4.5), leucocytosis (OR = 4.14; 95% CI: 1.5-11.6) and thrombocytopenia (OR = 3.70; 95% CI: 1.3-2.2) were risk factors for the occurrence of reactions during the study period. The identification of groups with an increased risk for developing reactions will allow for the timely development of a treatment plan to prevent nerve damage and, therefore, the appearance of the disabling sequelae associated with the stigma of leprosy.

Leprosy is an important health problem in Brazil despite extensive use of multidrug therapy. The nasal mucosa is the preferential site of entry and exit of Mycobacterium leprae, and although lesions have been found in the oral mucosa, its potential involvement in the transmission of leprosy bacilli has never been investigated. We investigated the presence of the M. leprae DNA in buccal swabs of leprosy patients (334) and household contacts (1288) through polymerase chain reaction (PCR), and correlated this with clinical and laboratorial evaluations. The overall positivity for patients and contacts was 18.26% and 6.83%, respectively. Subclinical infection among contacts was considered when PCR and anti-PGL-1 ELISA presented positive results. This study provides evidence that the oral mucosa may be a secondary site of M. leprae transmission and infection, and contacts with bacillary DNA may be actively involved in transmission. We have also shown that bacilli DNA is more frequently found in the oral mucosa of PB patients. Our findings have great epidemiological relevance and indicate an additional strategy for leprosy control programmes and dental clinics.