PCR amplification of the 531-bp fragment of the Mycobacterium leprae pra gene in fresh biopsy and slit skin smear samples was evaluated for its usefulness in the detection of leprosy bacilli in patients in Thailand. In multibacillary patients, 87.1% (27 of 31) of biopsy specimens and 41.9% (13 of 31) of slit skin smear specimens were positive by PCR, whereas in paucibacillary patients, 36.4% (8 of 22) of biopsy specimens and 18.2% (4 of 22) of slit skin smear specimens yielded detectable PCR amplification. Compared with other diagnostic procedures, PCR showed a clear advantage over both microscopic examination of slit skin smears and serologic detection of anti-phenolic glycolipid 1 antibody, especially in paucibacillary patients when bacterial indexes were 0 and seropositivity was only 6.25%. PCR was also evaluated for its potential to help monitor bacterial clearance in some of these patients during chemotherapeutic treatment. The PCR results on slit skin smear samples at 1, 3, and 6 months of chemotherapy showed that the number of PCR-positive cases of both multibacillary and paucibacillary types decreased sequentially. The results of this study are encouraging. However, investigation of a larger number of clinical specimens with an improvement in PCR methods, especially on slit skin smears, needs to be done before PCR can be established as a diagnostic procedure for leprosy patients and subclinical cases or as a tool for drug assessment. Leprosy, caused by Mycobacterium leprae, is still considered a major health problem in many developing countries. It is a chronic infectious disease of skin, nasal cavity, and peripheral nerves which eventually leads to disability, disfiguration, and socioeconomic problems (9, 11). There is no useful serologic test for the diagnosis of leprosy (6, 11). Early detection of the causative microorganisms is, therefore, the key element to early identification and treatment of patients and subclinical cases before the disease progresses and neural involvement occurs. These organisms are not cultivable on artificial media, and attempts to identify them by inoculating a susceptible animal such as the armadillo (13) and mouse footpads (3, 10, 14) have proved cumbersome and time-consuming. The routine bacteriologic diagnostic test, the demonstration of acidfast bacilli in skin smears (25), is not sufficiently sensitive or specific. This study was undertaken to evaluate the use of PCR as a means of diagnosis of leprosy and its potential to help assess the bacterial load reduction in patients during the course of chemotherapeutic treatment. MATERIALS AND METHODS Specimen collection. Slit skin smears and punch biopsies were obtained according to standard procedures (25) from 53 untreated leprosy patients at three institutes under the Department of Communicable Disease Control, Thailand: two skin clinics in Bangkok and a leprosy hospital in Samutprakarn province. Specimens were collected between October 1992 and March 1994. These patients were of both the paucibacillary (PB; having a negati...
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