Leishmania donovani: development and characterisation of a kinetoplast DNA probe and its use in the detection of parasites

An experimental challenge model for Leishmania donovani in beagle dogs, showing a similar pattern of parasite burden in the peripheral blood and liver

Leishmania donovani and Leishmania infantum are closely related species. However, the former is considered the causative agent for anthroponotic visceral leishmaniasis (AVL), while the latter is known to be responsible for zoonotic visceral leishmaniasis (ZVL) with dogs as the main reservoir host. Although molecular detection of L. donovani from naturally infected dogs has been reported in AVL endemic areas, the experimental infection of dogs with this species is very limited. Here, we constructed an experimental canine visceral leishmaniasis (CVL) model with L. donovani infection using beagle dogs. During an observation period of 8 months after parasite inoculation, few clinical symptoms were observed in the three inoculated dogs. The overall hematological and biochemical data of the dogs showed normal levels, and there were no remarkable changes in the peripheral CD4⁺, CD8⁺, CD25⁺, or FoxP3⁺ T cell populations. Liver biopsy sampling was conducted to monitor the parasite burden in the liver. A similar pattern of the amount of mitochondrial kinetoplast DNA was observed in the peripheral blood and liver by real-time PCR analysis. In addition, parasite antigens were detected from the liver biopsy sections by immunohistochemical analysis, further supporting the existence of parasites in the liver. These results showed a subclinical CVL model for L. donovani in beagle dogs with a similar kinetics of parasite burden in the peripheral blood and liver.

New Molecular Approach for the Detection of Kinetoplastida Parasites of Medical and Veterinary Interest

Kinetoplastids are protozoa containing a range of ubiquitous free_living species-pathogens of invertebrates, vertebrates and even some plants. Some of them are causative agents of canine vector-borne diseases. Their diagnosis is often missing in a gold standard. Here, we proposed a molecular approach for the diagnosis and study of Kinetoplastida. The TaqMan qPCR assays target the following genes: 24Sa LSU of Kinetoplastida, 28S LSU of Leishmania/ Trypanosoma spp., 5.8S rRNA of Trypanosoma spp., 18S SSU of Leishmania spp., kinetoplast minicircle DNA (kDNA) of L. donovani complex and kDNA of L. infantum, were designed, validated for their sensitivity (Se) and specificity (Sp) in silico and in vitro using a panel of known DNAs. They were then used to screen 369 blood samples (358 dogs, 2 equids, 9 monkeys). In addition, new 28S LSU primer sets are presented to use for Kinetoplastida's identification by PCR/sequencing. All qPCRs showed consistently high analytical sensitivities and reproducibility. They detect approximately 0.01 parasite/ mL blood for the kDNA based- qPCRs and at least a single cell-equivalent of rDNA for the other systems. Based on the sequencing results, after screening, Se and Sp were: 0. 919 and 0.971, 0.853 and 0.979, 1.00 and 0.987, 0.826 and 0.995 for all of Kinetoplastida, Leishmania/ Trypanosoma, Trypanosoma, Leishmania spp. specific qPCRs, respectively. kDNA based qPCRs were more sensitive and specific (Se: 1.00; Sp: 0.997). PCR/sequencing allowed the detection of Kinetoplastids in animal blood samples such as L. infantum, L. guyanensis, T. congolense, T. evansi and Bodo spp. The molecular approach proposed here is useful for epidemiological studies, fundamental research such as screening for new Kinetoplastida species, diagnosis and therapeutic follow-up. In addition, researchers are free to choose the molecular tools adapted to their aims.

Potential animal reservoirs (dogs and bats) of human visceral leishmaniasis due to Leishmania infantum in French Guiana

In French Guiana, cutaneous leishmaniasis is highly endemic, whereas no autochthonous case of visceral leishmaniasis have been reported so far. However, due to its proximity to Brazil which is highly endemic for visceral leishmaniasis, and the high transboundary population flow, an epidemiological challenge could arise at any time. As an overseas department and region and the largest outermost region of the European Union, epidemiological surveillance of visceral leishmaniasis is of great importance. Our study aimed to investigate the presence of Leishmania spp. in domestic (dogs) and sylvatic (bats) animals from French Guiana. Over the 2008-2018 period, samples from 349 animals were collected. They included blood from 179 autochthonous dogs and 59 bats, spleen samples from 33 bats and, blood from 78 military working dogs (MWD) collected before their departure from continental France and at the end of their four-month stay in French Guiana. Samples were screened using real-time polymerase chain reaction (qPCR) assays targeting Leishmania DNA followed by sequencing of 18S rRNA, kDNA and ITS2 genes. L. infantum was detected in 2.3% (8/349) of animals with 1.7% (3/179) of autochthonous dogs, 5.1% (4/78) of MWD returning from French Guiana, whereas they were negative before their departure. One of them dates back to 2012. All these dogs were positive for serological tests. In addition, L. infantum DNA was detectable in one bat spleen sample, belonging to Carollia perspicillata species. We report here for the first time an infection with L. infantum in dogs and bat from French Guiana. Our results suggest the existence of potential reservoir and transmission cycle for visceral leishmaniasis, at least since 2012, which was unknown in this territory until now. Further studies are needed to determine how these animals were infected and which vectors are involved in the transmission in this area.

Validity of the polymerase chain reaction in the diagnosis of clinically suspected cases of American visceral leishmaniasis

To test the validity of the polymerase chain reaction for diagnosing American visceral leishmaniasis, 88 suspected cases were studied. Diagnosis was confirmed in 47 (53.5%) and ruled out in 41 (46.5%) patients. Samples of bone marrow and peripheral blood were processed by polymerase chain reaction to evaluate the sensitivity and specificity of the test and its agreement beyond chance with microscopy examination. The polymerase chain reaction was positive in bone marrow of 100% of the patients with amastigotes seen with microscopy examination, and in 59.5% in those where no parasite were seen. Agreement beyond chance between visualization of the parasite in bone marrow aspirates and polymerase chain reaction was considered weak (Kappa = 0.41). Concordance between polymerase chain reaction of bone marrow aspirates and of peripheral blood was considered excellent (Kappa = 0.88). The test turned out positive in all bone marrow aspirates of those with the disease and whereas the positivity rate was 58.5% among those without the disease, with specificity rate of 41.5%.

Cutaneous leishmaniasis due to Leishmania chagasi/Le. infantum in an endemic area of Guarico State, Venezuela

This study reports cutaneous leishmaniasis (CL) caused by Leishmania chagasi/Le. infantum in Venezuela, with some atypical characteristics. Out of 63 cases of CL in the suburbs of Altagracia de Orituco, Guarico State, Venezuela, 30 presented clinical, parasitological, immunological and epidemiological features different from those of the classical CL known in the country. The initial lesion was small and nodular, which, if not treated, might progress to a superficial ulcer. No secondary infection was observed. The identification of the isolates was carried out by molecular techniques. Twelve species of phlebotomine sandflies were caught, the most abundant being Lutzomyia evansi and Lu. longipalpis s.l., known vectors of Le. chagasi/Le. infantum. The existence of Le. chagasi/Le. infantum and its vectors in an endemic area of CL has implications and we suggest that epidemiological studies should be carried out to obtain a clearer picture of the extent of this CL form in Venezuela.

Isolation and molecular identification of Leishmania chagasi from a bat (Carollia perspicillata) in northeastern Venezuela

This report describes the isolation of a Leishmania chagasi strain from a bat (Carollia perspicillata), and its identification using biological methods and molecular characterization. The parasites were isolated in an artificial culture medium from a blood sample extracted from a bat heart. The isolate was then inoculated into the footpads of Balb/c mice, which subsequently developed a typical nodular leishmanial lesion; the parasites were confirmed as Leishmania by smear and histopathology. Molecular characterization of the parasites was performed by polymerase chain reaction with species-specific primers, kDNA restriction pattern following Hae III endonuclease digestion and dot blot hybridization using a kDNA probe. This report demonstrates that bats can be hosts for L. chagasi species and suggests the need for studies to determine whether they may be involved in foci of visceral leishmaniasis.

Genetic homogeneity within Leishmania (L.) infantum isolated from human and dogs: the relationship with the sandfly fauna distribution in endemic areas of Nueva Esparta State, Venezuela

Leishmania infantum has been described as a highly polymorphic group of parasites, responsible for visceral leishmaniasis and cutaneous leishmaniasis. In this paper we report the life-cycle of L. (L.) infantum in an endemic area of visceral leishmaniasis in Venezuela, by using molecular diagnosis and characterization of parasites isolated from dogs, humans with visceral leishmaniasis and sand flies. The molecular characterization was carried out by use of kDNA restriction analysis, dot-blot hybridization with species-specific probes and RFLP of the PCR products. The results demonstrated that L. (L.) infantum is the parasite responsible for VL in the island. The parasites were revealed to be genetically homogeneous with no intra-specific differences between isolates from different individuals. The highest homology of the isolates was with L. (L.) infantum from the Old World rather than with L. (L.) chagasi from the New World. Additionally, we report the geographical distribution of Lutzomyia longipalpis, and the relationship with the transmission of L. (L.) infantum in the studied area.

Quantification of Leishmania infantum DNA by a real-time PCR assay with high sensitivity

A real-time PCR was developed to quantify Leishmania infantum kinetoplast DNA and optimized to reach a sensitivity of 0.0125 parasites/ml of blood. In order to analyze the incidence of heterogeneity and number of minicircles, we performed comparative PCR by using the Leishmania DNA polymerase gene as a reporter. Assays performed in both promastigote and amastigote stages showed variations among different L. infantum and Leishmania donovani strains and the stability of the minicircle numbers for a particular strain. Analysis of blood samples from a patient who presented with Mediterranean visceral leishmaniasis confirmed the reliability of such an assay for Leishmania quantification in biological samples and allowed an estimation of positivity thresholds of classical tests used for direct diagnosis of the disease; positivity thresholds were in the range of 18 to 42, 0.7 to 42, and 0.12 to 22.5 parasites/ml for microscopic examination, culture, and conventional PCR, respectively. At the time of diagnosis, parasitemia could vary by a wide range (32 to 188,700 parasites/ml, with a median of 837 parasites/ml), while in bone marrow, parasite load was more than 100 parasites per 10(6) nucleated human cells. After successful therapy, parasitemia levels remain lower than 1 parasite/ml. In the immunocompromised host, relapses correlate with an increase in the level of parasitemia, sometimes scanty, justifying the need for assays with high sensitivity. Such sensitivity allows the detection of Leishmania DNA in the blood of 21% of patients with no history of leishmaniasis living in the Marseilles area, where leishmaniasis is endemic. This technique may be useful for epidemiologic and diagnostic purposes, especially for the quantification of parasitemia at low levels during posttherapy follow-up.

Molecular diagnosis of leishmaniosis in dogs. Comparative application of traditional diagnostic methods and the proposed assay on clinical samples

Leishmaniosis is a zoonotic, parasitic disease caused by members of the genus Leishmania. The disadvantages of the traditional methods have currently rendered the polymerase chain reaction (PCR), the most reliable alternative for the laboratory diagnosis of this disease. Several relevant protocols have been described in the past but their application is in most cases limited to research use. The latter combined with the diagnostic problems that can be caused by the genetic variability of the different Leishmania strains or the presence of PCR inhibitors, indicate that an alternative approach should be followed for the development of a standard diagnostic tool for leishmaniosis. In the present study, we have evaluated several PCR-based protocols, in order to identify a primer combination that would allow the reliable detection of Leishmania DNA from clinical material and the verification of its results, in a manner that could be applicable even for routine use. The evaluation consisted of a BLAST verification of the specificity of the previously described primers, PCR testing, and optimisation of the reaction conditions. Our assessment was completed with the comparative evaluation of the results produced by the proposed PCR assay, light microscopy, and indirect fluorescent antibody technique (IFAT), on clinical samples collected from dogs suspected of leishmaniosis. The proposed assay which consists of a combination of two pairs of primers, targeted to different areas of the kinetoplast DNA of Leishmania spp., specific for Leishmania infantum, Leishmania donovani and Leishmania chagasi, showed optimum performance on our test samples, and detected 41.9% Leishmania-positive dogs from our 160 clinical cases. From the same number of cases, 46.25% were positive by IFAT (titre > or =200), and 19% by microscopic examination of lymph node aspirates.

Homologous minicircles in Leishmania donovani

Leishmania minicircular deoxyribonucleic acid (DNA) is arranged into different classes according to sequence. These classes differ substantially in sequence, despite species- and genus-specific regions, and are present in widely different copy numbers within and between Leishmania strains. Homologous minicircles have been identified in different species of Leishmania by comparing sequences of known minicircles. However, it is possible to select for minicircles of the same class by amplifying Leishmania DNA with polymerase chain reaction primers from the conserved and variable regions. This approach was used with 2 different minicircle classes in the L. donovani complex. In all isolates tested it was possible to amplify minicircles of the selected class.

The epidemiology of visceral leishmaniasis in east Africa: hints and molecular revelations

Visceral leishmaniasis appears in the form of notoriously devastating epidemics and as an endemic disease of sporadic nature. In an attempt to understand the nature of this difference and its underlying causes, and to identify possible mechanisms for the instigation of outbreaks, the current status of the characterization of the parasite, its taxonomy, host immunity and genetics, are reviewed with the main focus on eastern Africa, one of the places where the dichotomous epidemiology of the disease is most pronounced. The new molecular tools offer various insights into the understanding of the complex epidemiology of visceral leishmaniasis and the interplay between parasite and host factors. Further insights are also provided on the parts played by demography, genetic history and geography in shaping the overall global portrait of the disease.

A nested polymerase chain reaction for diagnosis and follow-up of human visceral leishmaniasis patients using blood samples

A nested polymerase chain reaction (PCR) assay for the diagnosis of human visceral leishmaniasis (VL) due to Leishmania infantum infection was developed using primers selected from the parasite's genomic deoxyribonucleic acid (DNA). The assay, which is based on the use of leucocytes separated from blood samples by Ficoll-Paque centrifugation, was compared with culture in vitro. Blood samples were collected from 17 patients in Spain with a history of clinical VL, 15 of whom were also infected with human immunodeficiency virus (HIV) (13 samples during the VL episode and 31 samples during post-treatment monitoring) and one sample was collected from each of 28 patients with HIV infection and fever but no history of VL. The nested PCR using blood detected all the cases of parasitologically confirmed, clinically active VL, while culture detected 92%. The nested PCR detected Leishmania DNA in 18% of the HIV-infected patients with fever and no history of VL, none of whom gave a positive culture. Follow-up examination of the VL patients by nested PCR and culture demonstrated the persistence of L. infantum in blood for a long time after treatment.

Comparison of various sample preparation methods for PCR diagnosis of visceral leishmaniasis using peripheral blood

We have compared various sample preparation methods for the PCR diagnosis of visceral leishmaniasis (VL) using peripheral blood samples and tested the influence of these protocols upon sensitivity. Four methods of lysis-DNA extraction were used with two types of blood samples: whole blood (WB) and buffy coat (BC). Comparisons were first carried out with seeded samples at various parasite concentrations. At high concentrations (> or = 1,000 parasites/ml), there were no significant differences in PCR sensitivity among the methods tested. At concentrations of < or = 100 parasites/ml, proteinase K (PK)-based methods proved clearly superior to guanidine-EDTA-based methods. Moreover, a 10-fold increase in sensitivity was observed for BC over that for WB. Thus, the best sensitivity was obtained with the BC prepared with PK-based methods. With this combination, the PCR reliably detected 10 parasites/ml but was inconsistent when the sample contained 1 parasite/ml of blood. The methods that yielded the highest sensitivities were evaluated with seven dogs and four human VL patients. Again, the utilization of the BC prepared with PK-based methods gave the best results. The optimization of each step of the assay (sample preparation, DNA extraction, and PCR conditions) yielded a highly sensitive tool for the diagnosis of VL using patient blood, thus avoiding more invasive diagnostic procedures and allowing the detection of low parasitemia during posttherapeutic follow-up.

Molecular tracking of infections by Leishmania infantum

Leishmania infantum is a major opportunistic parasite in patients with acquired immune deficiency syndrome and is very variable in these subjects. Isoenzyme characterization is not able to explain this variability, since half of the stocks isolated from patients co-infected with human immunodeficiency virus and Leishmania belong to zymodeme MON-1. Amplification of L. infantum minicircles by the polymerase chain reaction (PCR) and digestion of the amplified product to reveal restriction fragment length polymorphisms (RFLP) has proved very useful in distinguishing between relapses and reinfections in co-infected, treated patients. We have confirmed the existence of a leishmaniasis outbreak among intravenous drug users in north-east Spain, previously detected by isoenzymatic analysis. We have documented persistence of the same strain of Leishmania in 2 treated co-infected patients throughout several years, regardless of the theoretical rapid evolution ascribed to kinetoplast deoxyribonucleic acid minicircle sequences. We suggest using this PCR-RFLP technique to detect reinfections in treated co-infected subjects.

Detection and characterisation of parasites causing emerging zoonoses

Understanding the epidemiology of zoonotic parasitic infections is dependent upon the availability of accurate and sensitive diagnostic techniques. The development of molecular diagnostic methods, particularly those utilising PCR for the detection of zoonoses will contribute greatly to the identification and control of these pathogens, by increasing the speed of diagnosis, specificity and sensitivity, reproducibility and ease of interpretation. Molecular characterisation studies allow us to distinguish between closely related infectious agents and to document the patterns of transmission of 'strains' and species within populations. This will allow precise determinations to be made about the aetiological agent, its characteristics and the source of infection. This review focuses on recent detection and characterisation techniques for both emerging and re-emerging parasite zoonoses.