Detection of parasites of the Leishmania donovani-complex by a polymerase chain reaction-solution hybridization enzyme-linked immunoassay (PCR-SHELA)

Quantification of Leishmania infantum parasites in tissue biopsies by real-time polymerase chain reaction and polymerase chain reaction-enzyme-linked immunosorbent assay

Most of the experimental studies of Leishmania spp. infection require the determination of the parasite load in different tissues. Quantification of parasites by microscopy is not very sensitive and is time consuming, whereas culture microtitrations remain laborious and can be jeopardized by microbial contamination. The aim of this study was to quantify Leishmania infantum parasites by real-time polymerase chain reaction (PCR) using specific DNA TaqMan probes and to compare the efficacy of detection of this technique with a PCR-enzyme-linked immunosorbent assay (ELISA). For this purpose, spleen and liver samples from L. infantum-infected mice were collected during a 3-mo longitudinal study and analyzed by both methods. PCR-ELISA failed to quantify Leishmania spp. DNA in samples with very low or very high numbers of parasites. Real-time PCR was more sensitive than PCR-ELISA, detecting down to a single parasite, and enabled the parasite quantification over a wide, 5-log range. In summary, this study developed a method for absolute quantification of L. infantum parasites in infected organs using real-time TaqMan PCR.

QBC for the diagnosis of human and canine american visceral leishmaniasis: preliminary data

"Quantitative Buffy Coat" (QBC) is a direct and fast fluorescent method used for the identification of blood parasites. Since Leishmania chagasi circulates in blood, we decided to test it in American visceral leishmaniasis (AVL). Bone marrow (BM) and peripheral blood (PB) of 49 persons and PB of 31 dogs were analyzed. QBC was positive in BM of 11/11 patients with AVL and in 1/6 patients with other diseases. Amastigotes were identified in PB of 18/22 patients with AVL and in none without AVL. The test was positive in 30 out of the 31 seropositive dogs and in 28/28 dogs with Leishmania identified in other tissues. QBC is a promising method for diagnosis of human AVL, and possibly for the exam of PB of patients with AVL/AIDS, for the control of the cure and for the identification of asymptomatic carriers. Because it is fast and easy to collect and execute, QBC should be evaluated for programs of reservoir control.

Diagnosis of infections with Leishmania infantum using PCR-ELISA

On the basis of partial amplification of a cloned fragment of kDNA of Leishmania infantum which is specific for this species, we developed a PCR-ELISA technique which avoids the problems associated with classical diagnostic techniques. This technique was tested on 33 L. infantum strains from 19 different zymodemes, which were recognized equally. It was also used on human and canine clinical samples. PCR-ELISA has a higher sensitivity than the other techniques used (IFAT, parasite cultures, optical microscopy of stained samples) and permits detection of a minimum of 0.1 promastigotes or 1 fg of genomic DNA. PCR-ELISA can be used to diagnose human cutaneous leishmaniasis using material obtained by scraping the lesion margin, and human visceral leishmaniasis in HIV(+) individuals and canine leishmaniasis with peripheral blood samples. The presence of L. infantum in dogs with low antibody titres with IFAT technique (20 and 40) was demonstrated indicating that seroprevalence data from epidemiological studies underestimate the true rates of infection.

Optimized PCR using patient blood samples for diagnosis and follow-up of visceral Leishmaniasis, with special reference to AIDS patients

We developed a highly sensitive PCR method that enables the diagnosis and posttherapeutic follow-up of visceral leishmaniasis with patient blood. The PCR assay was thoroughly optimized by successive procedural refinements to increase its sensitivity and specificity. It was compared to in vitro cultivation as well as to direct examination of bone marrow and to serology. Two hundred thirty-seven patients presenting with clinical signs compatible with visceral leishmaniasis were included in the study. Thirty-six were diagnosed as having Mediterranean visceral leishmaniasis (MVL). Twenty-three of them, including 19 AIDS patients, were monitored during and after treatment over a period from 2 weeks to 3 years. Our PCR assay proved more sensitive than in vitro cultivation, direct examination, and serology for all patients. It is simple and can be adapted to routine hospital diagnostic procedures. For the primary diagnosis of MVL, the sensitivity of PCR versus that of cultivation was 97 versus 55% with peripheral blood and 100 versus 81% with bone marrow samples. Regarding posttherapeutic follow-up, overall, 48% of positive samples were detected by PCR only. Seven patients presented with a clinical relapse during the study; six relapses were detected at first by PCR only, sometimes a few weeks before the reappearance of signs or symptoms. We conclude that an optimized and well-mastered PCR assay with a peripheral blood sample is sufficient to provide a secure diagnosis for all immunocompromised patients and most immunocompetent patients. We also suggest systematic posttherapeutic monitoring by PCR with peripheral blood for immunocompromised patients.

PCR-ELISA for diagnosis of mucocutaneous leishmaniasis

In this work we demonstrate that the PCR-ELISA technique is sufficiently sensitive and specific for use as a diagnostic test in cases of mucocutaneous leishmaniasis. DNA was extracted from cultures of Leishmania braziliensis, Leishmania infantum, Leishmania tropica, Leishmania mexicana, Trypanosoma cruzi, and blood samples from individuals who presented a clinical diagnosis of leishmaniasis as well as from healthy individuals. The DNA was PCR amplified and the product obtained was hybridised with a biotin-labelled probe, the sequence of which was designed in our laboratory. The result of the hybridisation was visualised by means of an ELISA technique using antifluorescein antibody labelled with alkaline phosphatase and p-nitrophenylphosphate (pNFF) as chromogen. The optical density of the products of the pNFF hydrolysis was quantified in a spectrophotometer at a wavelength of 405 nm. Using this technique the percentage of detection was 83.3% in blood samples from patients clinically diagnosed as having mucocutaneous leishmaniasis. No false positive results were obtained.

A nested-PCR-based schizodeme method for identifying Leishmania kinetoplast minicircle classes directly from clinical samples and its application to the study of the epidemiology of Leishmania tropica in Pakistan

A nested PCR was developed to amplify the variable region of the kinetoplast minicircles of all Leishmania species which infect mammals. Each Leishmania parasite contains approximately 10,000 kinetoplast DNA minicircles, which are unequally distributed among approximately 10 minicircle classes. The PCR primers were designed to bind within the 120-bp conserved region which is common to all minicircle classes; the remaining approximately 600 bp of each minicircle is highly conserved within each minicircle class but highly divergent between classes. The nested PCR generated a strong signal from a minimum of 0.1 fg of Leishmania DNA. Restriction digests of the amplicons from the highest dilutions suggested that minicircles from only a limited number of minicircle classes had acted as template in the reaction. One PCR product was directly sequenced and found to be derived from only one minicircle class. Since the primers amplify all minicircle classes, this indicated that as little as 1/10 of one Leishmania parasite was present in the PCR template. This demonstrated that the nested PCR achieved very nearly the maximum theoretically possible sensitivity and is therefore a potentially useful method for diagnosis. The nested PCR was tested for sensitivity on 20 samples from patients from the Timargara refugee camp, Pakistan. Samples were collected by scraping out a small amount of tissue with a scalpel from an incision at the edge of the lesion; the tissue was smeared on one microscope slide and placed in a tube of 4 M guanidine thiocyanate, in which the sample was stable for at least 1 month. DNA for PCR was prepared by being bound to silica in the presence of 6 M guanidine thiocyanate; washed in guanidine thiocyanate, ethanol, and acetone; and eluted with 10 mM Tris-HCl. PCR products of the size expected for Leishmania tropica were obtained from 15 of the 20 samples in at least one of three replicate reactions. The negative samples were from lesions that had been treated with glucantime or were over 6 months old, in which parasites are frequently scanty. This test is now in routine use for the detection and identification of Leishmania parasites in our clinical laboratory. Fingerprints produced by restriction digests of the PCR products were defined as complex or simple. There were no reproducible differences between the complex restriction patterns of the kinetoplast DNA of any of the parasites from Timargara camp with HaeIII and HpaII. The simple fingerprints were very variable and were interpreted as being the product of PCR on a limited subset of minicircle classes, and consequently, it was thought that the variation was determined by the particular minicircle classes that had been represented in the template. The homogeneity of the complex fingerprints suggests that the present epidemic of cutaneous leishmaniasis in Timargara camp may be due to the spread of a single clone of L. tropica.

Single-step multiplex PCR assay for characterization of New World Leishmania complexes

We have developed a PCR assay for one-step differentiation of the three complexes of New World Leishmania (Leishmania braziliensis, Leishmania mexicana, and Leishmania donovani). This multiplex assay is targeted to the spliced leader RNA (mini-exon) gene repeats of these organisms and can detect all three complexes simultaneously, generating differently sized products for each complex. The assay is specific to the Leishmania genus and does not recognize related kinetoplastid protozoa, such as Trypanosoma cruzi, Trypanosoma brucei, and Crithidia fasciculata. It correctly identified Leishmania species with a broad geographic distribution in Central and South America. The sensitivity of the PCR amplification ranged from 1 fg to 10 pg of DNA (0.01 to 100 parasites), depending on the complex detected. Crude extracts of cultured parasites, prepared simply by boiling diluted cultures, served as excellent templates for amplification. Crude preparations of clinical material were also tested. The assay detected L. braziliensis in dermal scrapings from cutaneous leishmanial lesions, Leishmania chagasi in dermal scrapings of atypical cutaneous leishmaniasis, and L. mexicana from lesion aspirates from infected hamsters. We have minimized the material requirements and maximized the simplicity, rapidity, and informative content of this assay to render it suitable for use in laboratories in countries where leishmaniasis is endemic. This assay should be useful for rapid in-country identification of Leishmania parasites, particularly where different Leishmania complexes are found in the same geographical area.

Detection of Pneumocystis carinii in respiratory specimens by PCR-solution hybridization enzyme-linked immunoassay

By using a recently developed PCR-solution hybridization enzyme-linked assay (PCR-SHELA), we investigated Pneumocystis carinii in bronchoalveolar lavage fluid samples and induced sputa of patients with pneumocystosis. In detecting P. carinii, PCR-SHELA proved more sensitive than immunofluorescence staining or a single PCR and significantly more diagnostically specific than a nested PCR. Our data suggest that PCR-SHELA could be used to detect P. carinii organisms in respiratory samples, particularly in patients with uncertain diagnoses.