Molecular diagnosis of visceral leishmaniasis: a French study comparing a reference PCR method targeting kinetoplast DNA and a commercial kit targeting ribosomal DNA.

Abstract

Visceral leishmaniasis is a life-threatening disease caused by the Leishmania donovani species complex. For direct diagnosis, molecular diagnosis on blood and bone marrow is an increasingly used technique. For Leishmania, most PCR assays are laboratory-developed, but marketed PCR assays are now available and should be evaluated independently of manufacturers. The "quanty Leishmaniae, Clonit" kit was compared to a laboratory-developed method widely used in France and considered here as a reference method. Performances were evaluated on serial dilution assays, on 5 external quality controls and on 35 clinical samples. The reference method performed better than the Clonit kit with higher "performance scores": 20 of 28 (71%) and 4 of 12 (33%) vs 17 of 28 (61%) and 1 of 12 (8%) for the reference method and the Clonit kit, respectively. On clinical samples, six false negative results out of 27 positive samples (22%) were observed with the quanty Leishmaniae, Clonit method. These results are most likely due to the difference in the number of repeats of the PCR targets. The quanty Leishmaniae, Clonit, like most of marketed methods, targets the ribosomal DNA that has a lower number of copies than the kinetoplast DNA targeted by the reference PCR. This study confirms that the choice of target is crucial and should be taken into account in the development of new highly sensitive PCR methods. IMPORTANCE PCR revolutionized the direct diagnosis of infectious diseases, especially protozooses, where the infectious load is usually low. Commercial PCR methods are available and offer many advantages, including convenience and batch tracking as part of a quality system. For most parameters, the performance of commercial methods is at least as good as that of finely optimized methods developed in expert laboratories. This comparison work has not been done for the molecular diagnosis of visceral leishmaniasis. Leishmania sp. has a unique organelle, the kinetoplast, which corresponds to the mitochondrial DNA. It is organized into a large number of minicircles, which has made it a target for the development of diagnostic PCR. The quanty Leishmaniae, Clonit kit targeting ribosomal DNA was compared to a widely used laboratory-developed method based on kinetoplast DNA. This reference method gave significantly better results, probably due to the difference in the number of repeats of the PCR targets.