Nested polymerase chain reaction for detection of pathogenic leptospires.

Leptospirosis is a widespread zoonosis caused by pathogenic members of the genus Leptospira that has a great impact on human and veterinary public health. Early diagnosis of leptospirosis is important because severe lepto spiral infection can have a fulminant course. The available serological techniques for the diagnosis of leptospirosis have low sensitivity during the early stage of the disease. Efforts are being made to develop simpler, effective, efficient, and inexpensive diagnostic methods. In this work, we first evaluate a polymerase chain reaction (PCR) based method for diagnosis of leptospirosis. Primers were designed to amplify a 264 bp region within the lipL32 gene that is conserved among pathogenic Leptospira and absent in nonpathogenic species. The sensitivity and specificity of the assay were evaluated using 7 saprophytic serovars, 37 pathogenic serovars, and 15 other microorganisms. The method was very specific for pathogenic serovars, however, it lacked sensitivity. To enhance the sensitivity, another primer pair was designed to amplify a 183 bp region within the 264 bp region of the lipL32 gene and was used in a nested PCR assay. This approach was much more sensitive than conventional PCR.