Detection and quantification of Leishmania infantum in naturally and experimentally infected animal samples

Malnutrition Aggravates Alterations Observed in the Gut Structure and Immune Response of Mice Infected with Leishmania infantum

Malnutrition is a risk factor for developing visceral leishmaniasis and its severe forms. Our group demonstrated that malnourished animals infected with Leishmania infantum had severe atrophies in lymphoid organs and T cell subpopulations as well as altered levels of thymic and splenic chemotactic factors, all of which resulted in dysfunctional lymphoid microenvironments that promoted parasite proliferation. Here, we hypothesize that malnutrition preceding parasite infection leads to structural and immunological changes in the gut mucosae, resulting in a failure in the immune response sensed in the intestine. To evaluate this, we analyzed the immunopathological events resulting from protein malnutrition in the guts of BALB/c mice infected with L. infantum. We observed lymphocytic/lymphoplasmacytic inflammatory infiltrates and lymphoid hyperplasia in the duodenum of well-nourished-infected mice; such alterations were worsened when malnutrition preceded infection. Parasite infection induced a significant increase of duodenal immunoglobulin A (IgA) of well-nourished animals, but those levels were significantly decreased in malnourished-infected mice. In addition, increased levels of Th17-related cytokines in duodenums of malnourished animals supported local inflammation. Together, our results suggest that the gut plays a potential role in responses to L. infantum infection—and that such responses are impaired in malnourished individuals.

In silico and in vitro evaluation of primers for molecular differentiation of Leishmania species

Leishmaniasis is a zoonotic disease caused by over 20 species of protozoan parasites of the genus Leishmania. Infection is commonly spread by sandflies and produces a wide spectrum of clinical signs and symptoms. Therefore, from an epidemiological and therapeutic standpoint, it is important to detect and differentiate Leishmania spp. The objective of this study was to combinate in silico and in vitro strategies to evaluate the analytical specificity of primers previously described in the literature. According to electronic PCR (e-PCR) analysis, 23 out of 141 pairs of primers selected through literature search matched their previously reported analytical specificity. In vitro evaluation of nine of these primer pairs by quantitative PCR (qPCR) confirmed the analytical specificity of five of them at the level of Leishmania spp., L. mexicana complex or Leishmania and Viannia subgenera. Based on these findings, the combination of e-PCR and qPCR is suggested to be a valuable approach to maximize the specificity of new primer pairs for the laboratory diagnosis of infections with Leishmania spp.

High resolution melting assay in discrimination of the main etiologic agents of leishmaniasis in Iran

Background and Objectives:

The three old world Leishmania species i.e., L. major, L. tropica, and L. infantum are considered as potential etiological agents of the various clinical forms of leishmaniasis in Iran. Different species co-exist in some areas. Accurate differentiation between the species is essential for choosing an appropriate therapy. Conventional and gold standard methods for the detection and characterization of parasites are time-consuming, laborious, and have low sensitivity. A polymerase chain reaction followed by high resolution melting (PCR-HRM) analysis has been employed for detection and species identification. Most of the studies suffer from the use of multiple targets and/or requiring more than one reaction to identify a single sample. The present study aimed to design a PCR method based on the amplification of kinetoplast DNA minicircles (kDNA) and HRM analysis of the amplicons for rapid discrimination of the three mentioned species.

Materials and Methods:

DNA from reference strains including L. major, L. tropica, and L. infantum and fifty-eight strains subjected to PCR-HRM analysis targeting kDNA. All the samples were also analyzed by conventional kDNA-PCR.

Results:

The PCR-HRM analysis allowed discrimination between the three Old World species. The normalized HRM curves for the amplicons of kDNA indicated a unique and repeatable melting plot for each species, even in combination with human and mouse genomic DNA. Conventional kDNA-PCR could not properly discriminate L. tropica from L. infantum.

Conclusion:

PCR-HRM analysis of kDNA proved to be fast and accurate for discrimination of L. major, L. tropica, and L. infantum.

New features on the survival of human-infective Trypanosoma rangeli in a murine model: Parasite accumulation is observed in lymphoid organs

Trypanosoma rangeli is a non-pathogenic protozoan parasite that infects mammals, including humans, in Chagas disease-endemic areas of South and Central America. The parasite is transmitted to a mammalian host when an infected triatomine injects metacyclic trypomastigotes into the host's skin during a bloodmeal. Infected mammals behave as parasite reservoirs for several months and despite intensive research, some major aspects of T. rangeli-vertebrate interactions are still poorly understood. In particular, many questions still remain unanswered, e.g. parasite survival and development inside vertebrates, as no parasite multiplication sites have yet been identified. The present study used an insect bite transmission strategy to investigate whether the vector inoculation spot in the skin behave as a parasite-replication site. Histological data from the skin identified extracellular parasites in the dermis and hypodermis of infected mice in the first 24 hours post-infection, as well as the presence of inflammatory infiltrates in a period of up to 7 days. However, qPCR analyses demonstrated that T. rangeli is eliminated from the skin after 7 days of infection despite being still consistently found on circulating blood and secondary lymphoid tissues for up to 30 days post-infection. Interestingly, significant numbers of parasites were found in the spleen and mesenteric lymph nodes of infected mice during different periods of infection and steady basal numbers of flagellates are maintained in the host's bloodstream, which might behave as a transmission source to insect vectors. The presence of parasites in the spleen was confirmed by fluorescent photomicrography of free and cell-associated T. rangeli forms. Altogether our results suggest that this organ could possibly behave as a T. rangeli maintenance hotspot in vertebrates.

Differentiation of Leishmania (L.) infantum, Leishmania (L.) amazonensis and Leishmania (L.) mexicana Using Sequential qPCR Assays and High-Resolution Melt Analysis

Leishmania protozoa are the etiological agents of visceral, cutaneous and mucocutaneous leishmaniasis. In specific geographical regions, such as Latin America, several Leishmania species are endemic and simultaneously present; therefore, a diagnostic method for species discrimination is warranted. In this attempt, many qPCR-based assays have been developed. Recently, we have shown that L. (L.) infantum and L. (L.) amazonensis can be distinguished through the comparison of the Cq values from two qPCR assays (qPCR-ML and qPCR-ama), designed to amplify kDNA minicircle subclasses more represented in L. (L.) infantum and L. (L.) amazonensis, respectively. This paper describes the application of this approach to L. (L.) mexicana and introduces a new qPCR-ITS1 assay followed by high-resolution melt (HRM) analysis to differentiate this species from L. (L.) amazonensis. We show that L. (L.) mexicana can be distinguished from L. (L.) infantum using the same approach we had previously validated for L. (L.) amazonensis. Moreover, it was also possible to reliably discriminate L. (L.) mexicana from L. (L.) amazonensis by using qPCR-ITS1 followed by an HRM analysis. Therefore, a diagnostic algorithm based on sequential qPCR assays coupled with HRM analysis was established to identify/differentiate L. (L.) infantum, L. (L.) amazonensis, L. (L.) mexicana and Viannia subgenus. These findings update and extend previous data published by our research group, providing an additional diagnostic tool in endemic areas with co-existing species.

Visceral leishmaniasis: a practical strategy for quantitative molecular diagnosis in naturally infected dogs

The diagnosis of canine visceral leishmaniasis (CVL) has been a problem for public health services due to the variety of clinical signs similar to other diseases and low sensitivity and specificity of available tests. In this sense, our main objective was to develop a simple, rapid, and accurate quantitative real-time PCR (qPCR) diagnosis for CVL. Thus, low-invasive samples from bone marrow (BM), popliteal lymph nodes (PLN), and conjunctival swabs (CS) were selected from negative and VL-positive dogs, using as gold standard, immunological and parasitological tests performed with different tissues. Oligonucleotides for Leishmania infantum kDNA were designed and the limit of quantification and amplification efficiency of the qPCR were determined using tissue-specific standards produced with DNA from those different tissues, mixed with DNA from a known amount of L. infantum promastigotes. Endogenous control was used to validate a comparative Ct method, and tissue parasite concentrations were estimated by comparison with tissue-specific reference standard samples. The overall analysis of the qPCR data suggests the following ranking for tissue choice: PLN > BM > CS. Finally, we have concluded that this molecular approach simplifies and accelerates the quantitative diagnostic process because it is easy to perform, requiring no DNA dosing or standard curve application, and it shows good diagnostic parameters, especially when using popliteal lymph node samples.

Real-time PCR applications for diagnosis of leishmaniasis

Leishmaniasis is a vector-borne disease caused by many Leishmania species, which can infect both humans and other mammals. Leishmaniasis is a complex disease, with heterogeneous clinical manifestations ranging from asymptomatic infections to lesions at cutaneous sites (cutaneous leishmaniasis), mucosal sites (mucocutaneous leishmaniasis) or in visceral organs (visceral leishmaniasis), depending on the species and host characteristics. Often, symptoms are inconclusive and leishmaniasis can be confused with other co-endemic diseases. Moreover, co-infections (mainly with HIV in humans) can produce atypical clinical presentations. A correct diagnosis is crucial to apply the appropriate treatment and the use of molecular techniques in diagnosis of leishmaniasis has become increasingly relevant due to their remarkable sensitivity, specificity and possible application to a variety of clinical samples. Among them, real-time PCR (qPCR)-based approaches have become increasingly popular in the last years not only for detection and quantification of Leishmania species but also for species identification. However, despite qPCR-based methods having proven to be very effective in the diagnosis of leishmaniasis, a standardized method does not exist. This review summarizes the qPCR-based methods in the diagnosis of leishmaniasis focusing on the recent developments and applications in this field.

The use of kDNA minicircle subclass relative abundance to differentiate between Leishmania (L.) infantum and Leishmania (L.) amazonensis

BACKGROUND

Leishmaniasis is a neglected disease caused by many Leishmania species, belonging to subgenera Leishmania (Leishmania) and Leishmania (Viannia). Several qPCR-based molecular diagnostic approaches have been reported for detection and quantification of Leishmania species. Many of these approaches use the kinetoplast DNA (kDNA) minicircles as the target sequence. These assays had potential cross-species amplification, due to sequence similarity between Leishmania species. Previous works demonstrated discrimination between L. (Leishmania) and L. (Viannia) by SYBR green-based qPCR assays designed on kDNA, followed by melting or high-resolution melt (HRM) analysis. Importantly, these approaches cannot fully distinguish L. (L.) infantum from L. (L.) amazonensis, which can coexist in the same geographical area.

METHODS

DNA from 18 strains/isolates of L. (L.) infantum, L. (L.) amazonensis, L. (V.) braziliensis, L. (V.) panamensis, L. (V.) guyanensis, and 62 clinical samples from L. (L.) infantum-infected dogs were amplified by a previously developed qPCR (qPCR-ML) and subjected to HRM analysis; selected PCR products were sequenced using an ABI PRISM 310 Genetic Analyzer. Based on the obtained sequences, a new SYBR-green qPCR assay (qPCR-ama) intended to amplify a minicircle subclass more abundant in L. (L.) amazonensis was designed.

RESULTS

The qPCR-ML followed by HRM analysis did not allow discrimination between L. (L.) amazonensis and L. (L.) infantum in 53.4% of cases. Hence, the novel SYBR green-based qPCR (qPCR-ama) has been tested. This assay achieved a detection limit of 0.1 pg of parasite DNA in samples spiked with host DNA and did not show cross amplification with Trypanosoma cruzi or host DNA. Although the qPCR-ama also amplified L. (L.) infantum strains, the C_q values were dramatically increased compared to qPCR-ML. Therefore, the combined analysis of C_q values from qPCR-ML and qPCR-ama allowed to distinguish L. (L.) infantum and L. (L.) amazonensis in 100% of tested samples.

CONCLUSIONS

A new and affordable SYBR-green qPCR-based approach to distinguish between L. (L.) infantum and L. (L.) amazonensis was developed exploiting the major abundance of a minicircle sequence rather than targeting a hypothetical species-specific sequence. The fast and accurate discrimination between these species can be useful to provide adequate prognosis and treatment.

Protein malnutrition promotes dysregulation of molecules involved in T cell migration in the thymus of mice infected with Leishmania infantum

Protein malnutrition, the most deleterious cause of malnutrition in developing countries, has been considered a primary risk factor for the development of clinical visceral leishmaniasis (VL). Protein malnutrition and infection with Leishmania infantum leads to lymphoid tissue disorganization, including changes in cellularity and lymphocyte subpopulations in the thymus and spleen. Here we report that protein malnutrition modifies thymic chemotactic factors by diminishing the CCL5, CXCL12, IGF1, CXCL9 and CXCL10 protein levels in infected animals. Nevertheless, T cells preserve their migratory capability, as they were able to migrate ex vivo in response to chemotactic stimuli, indicating that malnutrition may compromise the thymic microenvironment and alter in vivo thymocyte migration. Decrease in chemotactic factors protein levels was accompanied by an early increase in the parasite load of the spleen. These results suggest that the precondition of malnutrition is affecting the cell-mediated immune response to L. infantum by altering T cell migration and interfering with the capacity of protein-deprived animals to control parasite spreading and proliferation. Our data provide evidence for a disturbance of T lymphocyte migration involving both central and peripheral T-cells, which likely contribute to the pathophysiology of VL that occurs in malnourished individuals.