A PCR and RFLP-based molecular diagnostic algorithm for visceral leishmaniasis

Objective:To determine an algorithm for molecular diagnosis of visceral leishmaniasis(VL)by kinetoplast DNA(kDNA)(RV1/RV2)and internal transcriber spacer(ITS1)(LITSR/L5.8 S)polymerase chain reaction(PCR),complemented by ITS 1 PCR restriction fragment length polymorphism(RFLP),using peripheral blood or bone marrow aspirate from patients with suspected VL.Methods:Biological samples were submitted to the gold standard for the diagnosis of VL and molecular diagnosis represented by ITS 1 PCR,kDNA PCR,and ITS 1 PCR RFLP.The samples were obtained from seven groups:groupⅠ,82 samples from patients with confirmed VL;groupⅡ,16 samples from patients under treatment for VL;groupⅢ,14 samples from dogs with canine visceral leishmaniasis(CVL);groupⅣ,a pool of six experimentally infected sandflies(Lutzomya longipalpis);group V,18 samples from patients with confirmed tegumentary leishmaniasis(TL)and groupsⅥandⅦwere from control groups without VL.Results:The following gold standard and molecular examination results were obtained for each of the seven groups:groupⅠ:parasitologic and immunochromatographic tests showed a sensitivity of 76.3%(61 of 80)and 68.8%(55 of 80),respectively,and a sensitivity of 97.6%(80 of 82)and 92.7%(76 of 82)by ITS1 and kDNA PCR,respectively.After ITS1 PCR RFLP(HaeⅢ)analysis of the 80 positive samples,52.5%(42 of 80)generated three fragments of 180,70,and 50 bp,corresponding to the pattern of Leishmania infantum infantum;groupⅡ:negative for the parasitologic methods and positive for IrK39(100%,16 of 16),presented 12.5%(2 of 16)of positivity by ITS 1 PCR and 25.0%(4 of 16)by kDNA PCR;groupⅢ:positive in the parasitologic and serologic tests(100%,14 of 14),presented 85.7%(12 of 14)of positivity by ITS1 PCR and kDNA PCR.ITS1 PCR RFLP showed that 83.3%(10 of 12)of the canine samples contained parasites with profiles similar to L.infantum;groupⅣpresented amplifications by ITS1 PCR and kDNA PCR.ITS1 PCR products were analyzed by RFLP,generating a profile similar to that of L.infantum;groupⅤ:positive in the parasitologic examination(100%,18 of 18),presented 72.2%(13 of 18)of the samples by ITS1 PCR positive.A total of 69.2%(9 of 13)showed profiles corresponding to a Viannia complex by ITS1 PCR RFLP;and groupⅥand groupⅥwere negative by ITS 1 and kDNA molecular tests.Comparing the molecular results with the parasitologic and serologic diagnosis from groupⅠ,almost perfect agreement was found(κboth>0.80,P<0.001).ITS1 and RV1/RV2 PCR detected 90.2%(74 of 82)of the samples.Two samples positive by RV1/RV2 were negative by LITSR/L5.8 S,and six samples positive by LITSR/L5.8 S were negative by RV1/RV2.Therefore,these two systems complemented each other;they diagnosed 100%of the samples as belonging to the Leishmania genus.Conclusions:We suggest an algorithm for the molecular diagnosis of VL,which must consider previous parasitologic and serologic(immunochromatographic)diagnoses,and should combine kDNA and ITS1 to determine the Leishmania subgenus using RFLP as a complement method to define the L.infantum species.