BACKGROUND: Mycobacterium leprae was thought the exclusive causative agent of leprosy until Mycobacterium lepromatosis was identified in a rare form of leprosy known as diffuse lepromatous leprosy (DLL).
METHODS: We isolated M. lepromatosis from a patient with DLL and propagated it in athymic nude mouse footpads. Genomic analysis of this strain (NHDP-385) identified a unique repetitive element, RLPM, upon which a specific real-time quantitative PCR (qPCR) assay was developed. The RLPM assay, and our previously developed RLEP qPCR for M. leprae, were validated as clinical diagnostic assays according to Clinical Laboratory Improvement Amendments guidelines. We tested DNA from archived histological sections, patient specimens from the United States (US), Philippines, and Mexico, and US wild armadillos.
RESULTS: The limit of detection for the RLEP and RLPM assays is 30 M. leprae per specimen (0.76 bacilli per reaction; CV%: 0.65-2.44) and 122 M. lepromatosis per specimen (3.05 bacilli per reaction; CV%: 0.84-2.9), respectively. In histological sections (n=10), one lepromatous leprosy (LL), one DLL, and three Lucio reactions contained M. lepromatosis; two LL and two Lucio reactions contained M. leprae; one LL contained both species. M. lepromatosis was detected in 3/218 (1.38%) US biopsies. All Philippines specimens (n=180) were M. lepromatosis negative and M. leprae positive. Conversely, 15/47 (31.91%) Mexican specimens were positive for M. lepromatosis; 19/47 (40.43%) were positive for M. leprae; 2/47 (4.26%) contained both organisms. All armadillos were M. lepromatosis negative.
CONCLUSIONS: The RLPM and RLEP assays will aid healthcare providers in clinical diagnosis and surveillance of leprosy.
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